Publications by authors named "Rogelio Santiago"

34 Publications

Elucidating the multifunctional role of the cell wall components in the maize exploitation.

BMC Plant Biol 2021 Jun 2;21(1):251. Epub 2021 Jun 2.

Facultad, de Biología, Departamento de Biología Vegetal Y Ciencias del Suelo, Universidad de Vigo, As Lagoas Marcosende, 36310, Vigo, Spain.

Background: Besides the use of maize grain as food and feed, maize stover can be a profitable by-product for cellulosic ethanol production, whereas the whole plant can be used for silage production. However, yield is reduced by pest damages, stem corn borers being one of the most important yield constraints. Overall, cell wall composition is key in determining the quality of maize biomass, as well as pest resistance. This study aims to evaluate the composition of the four cell wall fractions (cellulose, hemicellulose, lignin and hydroxycinnamates) in diverse maize genotypes and to understand how this composition influences the resistance to pests, ethanol capacity and digestibility.

Results: The following results can be highlighted: (i) pests' resistant materials may show cell walls with low p-coumaric acid and low hemicellulose content; (ii) inbred lines showing cell walls with high cellulose content and high diferulate cross-linking may present higher performance for ethanol production; (iii) and inbreds with enhanced digestibility may have cell walls poor in neutral detergent fibre and diferulates, combined with a lignin polymer composition richer in G subunits.

Conclusions: Results evidence that there is no maize cell wall ideotype among the tested for optimal performance for various uses, and maize plants should be specifically bred for each particular application.
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http://dx.doi.org/10.1186/s12870-021-03040-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8170779PMC
June 2021

Elucidating compositional factors of maize cell walls contributing to stalk strength and lodging resistance.

Plant Sci 2021 Jun 19;307:110882. Epub 2021 Mar 19.

Área de Fisiología Vegetal, Facultad de Ciencias Biológicas y Ambientales, Universidad de León, E-24071, León, Spain. Electronic address:

Lodging is one of the causes of maize (Zea mays L.) production losses worldwide and, at least, the resistance to stalk lodging has been positively correlated with stalk strength. In order to elucidate the putative relationship between cell wall, stalk strength and lodging resistance, twelve maize inbreds varying in rind penetration strength and lodging resistance were characterized for cell wall composition and structure. Stepwise multiple regression indicates that H lignin subunits confer a greater rind penetration strength. Besides, the predictive model for lodging showed that a high ferulic acid content increases the resistance to lodging, whereas those of diferulates decrease it. These outcomes highlight that the strength and lodging susceptibility of maize stems may be conditioned by structural features of cell wall rather than by the net amount of cellulose, hemicelluloses and lignin. The results presented here provide biotechnological targets in breeding programs aimed at improving lodging in maize.
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http://dx.doi.org/10.1016/j.plantsci.2021.110882DOI Listing
June 2021

Maize Resistance to Stem Borers Can Be Modulated by Systemic Maize Responses to Long-Term Stem Tunneling.

Front Plant Sci 2020 11;11:627468. Epub 2021 Mar 11.

Misión Biológica de Galicia (CSIC), El Palacio-Salcedo, Pontevedra, Spain.

Limited attention has been paid to maize ( L.) resistance induced by corn borer damage, although evidence shows that induced defenses have lower resource allocation costs than constitutive defenses. Maize responses to short- and long-term feeding by the Mediterranean corn borer (MCB, ) have been previously studied, but the suggested differences between responses could be due to experimental differences. Therefore, in the current study, a direct comparison between short- and long-term responses has been made. The objectives were (i) to determine changes in the level of antibiosis of the stems induced by feeding of larvae for 2days (short-term feeding) and 9days (long-term feeding), (ii) to characterize the metabolome of the stems' short- and long-term responses to borer feeding, and (iii) to look for metabolic pathways that could modulate plant resistance to MCB. Defenses were progressively induced in the resistant inbred, and constitutive defenses were broken down in the susceptible inbred. Results suggest that the different resistance levels of the two inbreds to stem tunneling by MCB could depend on their ability to establish a systemic response. Based on these results, a high throughput look for specific metabolites implicated in systemic induced resistance to maize stem borers is recommended; the current focus on constitutive defense metabolites has not been successful in finding molecules that would be valuable tools for pest control.
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http://dx.doi.org/10.3389/fpls.2020.627468DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7991579PMC
March 2021

Unraveling the role of maize (Zea mays L.) cell-wall phenylpropanoids in stem-borer resistance.

Phytochemistry 2021 May 12;185:112683. Epub 2021 Feb 12.

Departamento Biología Vegetal y Ciencias del Suelo, Facultad de Biología, UA Agrobiología Ambiental, Calidad de Suelos y Plantas, Universidad de Vigo, As Lagoas Marcosende, 36310, Vigo, Spain.

The cell wall putatively plays a role in host-plant resistance to phytopathogens. Here, we investigated which cell wall-bound phenolic compounds have determining roles in maize (Zea mays) resistance to attack by the Mediterranean corn borer Sesamia nonagrioides (Lefèbvre). Diverse sets of maize genotypes having contrasting hydroxycinnamate contents and borer resistance levels were evaluated. The interdependent relationships among some cell wall-bound phenolic compounds, such as ferulic acid and its dimers, or p-coumaric acid and syringyl lignin subunits, were analyzed. Both p-coumaric acid and syringyl momoners showed significant negative correlations with damage, as assessed by tunnel lengths, caused by S. nonagrioides larvae. Thus, the use of cell wall-bound p-coumaric acid in pest-resistant crop breeding programs is advisable.
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http://dx.doi.org/10.1016/j.phytochem.2021.112683DOI Listing
May 2021

Genomics of Maize Resistance to Fusarium Ear Rot and Fumonisin Contamination.

Toxins (Basel) 2020 06 30;12(7). Epub 2020 Jun 30.

Misión Biológica de Galicia (CSIC), Apdo. 28, 36080 Pontevedra, Spain.

Food contamination with mycotoxins is a worldwide concern, because these toxins produced by several fungal species have detrimental effects on animal and/or human health. In maize, fumonisins are among the toxins with the highest threatening potential because they are mainly produced by , which is distributed worldwide. Plant breeding has emerged as an effective and environmentally safe method to reduce fumonisin levels in maize kernels, but although phenotypic selection has proved effective for improving resistance to fumonisin contamination, further resources should be mobilized to meet farmers' needs. Selection based on molecular markers linked to quantitative trait loci (QTL) for resistance to fumonisin contamination or/and genotype values obtained using prediction models with markers distributed across the whole genome could speed up breeding progress. Therefore, in the current paper, previously identified genomic regions, genes, and/or pathways implicated in resistance to fumonisin accumulation will be reviewed. Studies done until now have provide many markers to be used by breeders, but to get further insight on plant mechanisms to defend against fungal infection and to limit fumonisin contamination, the genes behind those QTLs should be identified.
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http://dx.doi.org/10.3390/toxins12070431DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7404995PMC
June 2020

Mapping of resistance to corn borers in a MAGIC population of maize.

BMC Plant Biol 2019 Oct 17;19(1):431. Epub 2019 Oct 17.

Misión Biológica de Galicia, Spanish National Research Council (CSIC), Apartado 28, 36080, Pontevedra, Spain.

Background: Corn borers constitute an important pest of maize around the world; in particular Sesamia nonagrioides Lefèbvre, named Mediterranean corn borer (MCB), causes important losses in Southern Europe. Methods of selection can be combined with transgenic approaches to increase the efficiency and durability of the resistance to corn borers. Previous studies of the genetic factors involved in resistance to MCB have been carried out using bi-parental populations that have low resolution or using association inbred panels that have a low power to detect rare alleles. We developed a Multi-parent Advanced Generation InterCrosses (MAGIC) population to map with high resolution the genetic determinants of resistance to MCB.

Results: We detected multiple single nucleotide polymorphisms (SNPs) of low effect associated with resistance to stalk tunneling by MCB. We dissected a wide region related to stalk tunneling in multiple studies into three smaller regions (at ~ 150, ~ 155, and ~ 165 Mb in chromosome 6) that closely overlap with regions associated with cell wall composition. We also detected regions associated with kernel resistance and agronomic traits, although the co-localization of significant regions between traits was very low. This indicates that it is possible the concurrent improvement of resistance and agronomic traits.

Conclusions: We developed a mapping population which allowed a finer dissection of the genetics of maize resistance to corn borers and a solid nomination of candidate genes based on functional information. The population, given its large variability, was also adequate to map multiple traits and study the relationship between them.
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http://dx.doi.org/10.1186/s12870-019-2052-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6796440PMC
October 2019

Effect of Long-Term Feeding by Borers on the Antibiotic Properties of Corn Stems.

J Econ Entomol 2019 05;112(3):1439-1446

Universidad de Vigo, Facultad de Biología, Dpto. Biología Vegetal y Ciencias del Suelo, Unidad Asociada BVE1-UVIGO y Misión Biológica de Galicia (CSIC), Campus As Lagoas Marcosende, Vigo, Spain.

Plant long-term response against chewing insects could become stronger than initial reactions and even turn into systemic. The objectives of the present study were 1) to evaluate whether the long-running attack to the stem by corn borers can improve the stem antibiotic properties; 2) to check whether hydroxycinnamic acids could be involved in this antibiotic response; 3) and to check whether elicitation by Sesamia nonagrioides Lef. (Lepidoptera: Noctuidae) regurgitant could activate long-term plant responses. In this sense, we observed that long-term feeding by S. nonagrioides larvae induced genotype-dependent changes in stem antibiosis and phenolic profiles, but the hydroxycinnamate content does not have a significant role in the systemic defense induced by the attack. In addition, response to long-term feeding by larvae could not be fully mimicked by elicitation using S. nonagrioides regurgitant alone. For the first time, it has been demonstrated that 'long-term' attack to the stem by corn borers can increase the stem antibiotic properties, and this has to be considered attending to breeding strategies.
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http://dx.doi.org/10.1093/jee/toz035DOI Listing
May 2019

Maize Stem Response to Long-Term Attack by .

Front Plant Sci 2018 23;9:522. Epub 2018 Apr 23.

Misión Biológica de Galicia, Spanish Council for Scientific Research (MBG-CSIC), Pontevedra, Spain.

Plants defend themselves against herbivores by activating a plethora of genetic and biochemical mechanisms aimed at reducing plant damage and insect survival. The short-term plant response to insect attack is well understood, but less is known about the maintenance of this response over time. We performed transcriptomic and metabolomics analyses in order to identify genes and metabolites involved in the long-term response of maize to attack by the corn borer . To determine the role of elicitors present in caterpillar secretions, we also evaluated the response of maize stem challenged with insect regurgitates. The integrative analysis of the omics results revealed that the long-term response in maize is characterized by repression of the primary metabolism and a strong redox response, mainly mediated by germin-like proteins to produce anti-nutritive and toxic compounds that reduce insect viability, and with the glutathione-ascorbate cycle being crucial to minimize the adverse effects of reactive oxygen species (ROS) on the plant. Our results suggest that different defense mechanisms are involved in the long-term response compared to those reported during the early response. We also observed a marginal effect of the caterpillar regurgitates on the long-term defensive response.
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http://dx.doi.org/10.3389/fpls.2018.00522DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5925969PMC
April 2018

Methods for Determining Cell Wall-Bound Phenolics in Maize Stem Tissues.

J Agric Food Chem 2018 Feb 26;66(5):1279-1284. Epub 2018 Jan 26.

BioDiscovery Institute, University of North Texas , Denton, Texas 76203, United States.

We compared two methods with different sample pretreatment, hydrolysis, and separation procedures to extract cell wall-bound phenolics. The samples were pith and rind tissues from six maize inbred lines reportedly containing different levels of cell wall-bound phenolics. In method 1, pretreated samples were extracted with a C solid-phase extraction cartridge, and it took 6 days to complete. In method 2, phenolics were extracted from crude samples with ethyl acetate, it took 2 days to complete, and the cost per sample was reduced more than 60%. Both methods extracted more 4-coumarate than ferulate. Overall, method 1 yielded more 4-coumarate, while method 2 yielded more ferulate. The lack of a genotype × method interaction and significant correlations between the results obtained using the two methods indicate that both methods are reliable for use in large-scale plant breeding programs. Method 2, scaled, is proposed for general plant biology research.
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http://dx.doi.org/10.1021/acs.jafc.7b05752DOI Listing
February 2018

Chemical Changes during Maize Tissue Aging and Its Relationship with Mediterranean Corn Borer Resistance.

J Agric Food Chem 2017 Oct 16;65(42):9180-9185. Epub 2017 Oct 16.

Universidad de Vigo , Dpto. Biología Vegetal y Ciencias del Suelo, Unidad Asociada BVE1-UVIGO y Misión Biológica de Galicia (CSIC), Campus As Lagoas Marcosende, 36310 Vigo, Spain.

The Mediterranean corn borer (MCB), Sesamia nonagrioides Lef, is an important pest of maize in temperate areas, causing significant stalk lodging and yield losses. The main goals of this study were to determine possible changes in chemical traits (phenols, flavonoids, anthocyanins, sugars, fibers, and lignin) during plant development after the flowering stage and to assess how those traits may differ in diverse genotypes of maize, such as MCB resistant and susceptible. Higher values for some particular traits in more mature tissues seemed to increase their effectiveness against the MCB attack. A decreased amount of borer damage in the field was recorded in the resistant inbred line and in older tissues (7.90 cm vs 31.70 cm as the mean for the stalk tunnel length). In accordance with these results, the resistant inbred line showed a higher degree of hemicellulose cross-linkage (due to ferulic and diferulic acids), higher soluble sugar content, and higher stalk strength. The use of resistant varieties and early sowings is highly recommended as an integrated approach to reduce the yield losses produced by this pest.
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http://dx.doi.org/10.1021/acs.jafc.7b02911DOI Listing
October 2017

Defensive changes in maize leaves induced by feeding of Mediterranean corn borer larvae.

BMC Plant Biol 2017 02 15;17(1):44. Epub 2017 Feb 15.

Misión Biológica de Galicia CSIC, Apartado 28, Pontevedra, 36080, Spain.

Background: Plants can respond to insect attack via defense mechanisms that reduce insect performance. In this study, we examined the effects of several treatments applied to two maize genotypes (one resistant, one susceptible) on the subsequent growth and survival of Sesamia nonagrioides Lef. (Mediterranean corn borer, MCB) larvae. The treatments were infestation with MCB larvae, application of MCB regurgitant upon wounding, wounding alone, or exposure to methyl jasmonate, and they were applied at the V6-V8 stage of maize development. We also monitored changes in the concentrations of compounds known to be involved in constitutive resistance, such as cell wall-bound hydroxycinnamates and benzoxazinoids.

Results: In both maize genotypes, the leaves of plants pre-infested with MCB larvae were less suitable for larval development than those from untreated plants. Application of MCB regurgitant upon wounding, and wounding itself, resulted in leaf tissues becoming less suitable for larval growth than those of pre-infested plants, suggesting that there could be herbivore-associated effector molecules that suppress some wounding responses. A single application of MCB regurgitant did not seem to mimic feeding by MCB larvae, although the results suggested that regurgitant deposited during feeding may have enhanced ferulates and diferulates synthesis in infested vs. control plants. Jasmonic acid may play a role in mediating the maize response to MCB attack, but it did not trigger hydroxycinnamate accumulation in the leaves to a level comparable to that induced by larval leaf feeding. The EP39 maize genotype showed an increase in leaf cell wall strength by increasing hemicellulose cross-linking in response to MCB attack, while induced defenses in the EP42 plants appeared to reflect a broader array of resistance mechanisms.

Conclusions: The results indicated that leaf feeding by MCB larvae can increase leaf antibiosis against MCB in two maize genotypes with contrasting levels of resistance against this borer. Also, the larval regurgitant played a positive role in eliciting a defense response. We determined the effects of the plant response on larval growth, and detected defense compounds related to borer resistance.
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http://dx.doi.org/10.1186/s12870-017-0991-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5312564PMC
February 2017

Hydroxycinnamate Synthesis and Association with Mediterranean Corn Borer Resistance.

J Agric Food Chem 2016 Jan 12;64(3):539-51. Epub 2016 Jan 12.

Misión Biológica de Galicia (CSIC) , Apartado 28, 36080 Pontevedra, Spain.

Previous results suggest a relationship between maize hydroxycinnamate concentration in the pith tissues and resistance to stem tunneling by Mediterranean corn borer (MCB, Sesamia nonagrioides Lef.) larvae. This study performs a more precise experiment, mapping an F2 derived from the cross between two inbreds with contrasting levels for hydroxycinnamates EP125 × PB130. We aimed to co-localize genomic regions involved in hydroxycinnamate synthesis and resistance to MCB and to highlight the particular route for each hydroxycinnamate component in relation to the better known phenylpropanoid pathway. Seven quantitative trait loci (QTLs) for p-coumarate, two QTLs for ferulate, and seven QTLs for total diferulates explained 81.7, 26.9, and 57.8% of the genotypic variance, respectively. In relation to borer resistance, alleles for increased hydroxycinnamate content (affecting one or more hydroxycinnamate compounds) could be associated with favorable effects on stem resistance to MCB, particularly the putative role of p-coumarate in borer resistance.
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http://dx.doi.org/10.1021/acs.jafc.5b04862DOI Listing
January 2016

Genetic Factors Involved in Fumonisin Accumulation in Maize Kernels and Their Implications in Maize Agronomic Management and Breeding.

Toxins (Basel) 2015 Aug 20;7(8):3267-96. Epub 2015 Aug 20.

Misión Biológica de Galicia (CSIC), Box 28, Pontevedra 36080, Spain.

Contamination of maize with fumonisins depends on the environmental conditions; the maize resistance to contamination and the interaction between both factors. Although the effect of environmental factors is a determinant for establishing the risk of kernel contamination in a region, there is sufficient genetic variability among maize to develop resistance to fumonisin contamination and to breed varieties with contamination at safe levels. In addition, ascertaining which environmental factors are the most important in a region will allow the implementation of risk monitoring programs and suitable cultural practices to reduce the impact of such environmental variables. The current paper reviews all works done to address the influence of environmental variables on fumonisin accumulation, the genetics of maize resistance to fumonisin accumulation, and the search for the biochemical and/or structural mechanisms of the maize plant that could be involved in resistance to fumonisin contamination. We also explore the outcomes of breeding programs and risk monitoring of undertaken projects.
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http://dx.doi.org/10.3390/toxins7083267DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4549750PMC
August 2015

Cell wall modifications triggered by the down-regulation of Coumarate 3-hydroxylase-1 in maize.

Plant Sci 2015 Jul 28;236:272-82. Epub 2015 Apr 28.

Centre for Research in Agricultural Genomics (CRAG) Consorci CSIC-IRTA-UAB-UB Edifici CRAG Campus de Bellaterra de la UAB, 08193 Cerdanyola del Valles, Barcelona, Spain. Electronic address:

Coumarate 3-hydroxylase (C3H) catalyzes a key step of the synthesis of the two main lignin subunits, guaiacyl (G) and syringyl (S) in dicotyledonous species. As no functional data are available in regards to this enzyme in monocotyledonous species, we generated C3H1 knock-down maize plants. The results obtained indicate that C3H1 participates in lignin biosynthesis as its down-regulation redirects the phenylpropanoid flux: as a result, increased amounts of p-hydroxyphenyl (H) units, lignin-associated ferulates and the flavone tricin were detected in transgenic stems cell walls. Altogether, these changes make stem cell walls more degradable in the most C3H1-repressed plants, despite their unaltered polysaccharide content. The increase in H monomers is moderate compared to C3H deficient Arabidopsis and alfalfa plants. This could be due to the existence of a second maize C3H protein (C3H2) that can compensate the reduced levels of C3H1 in these C3H1-RNAi maize plants. The reduced expression of C3H1 alters the macroscopic phenotype of the plants, whose growth is inhibited proportionally to the extent of C3H1 repression. Finally, the down-regulation of C3H1 also increases the synthesis of flavonoids, leading to the accumulation of anthocyanins in transgenic leaves.
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http://dx.doi.org/10.1016/j.plantsci.2015.04.007DOI Listing
July 2015

Ectopic lignification in primary cellulose-deficient cell walls of maize cell suspension cultures.

J Integr Plant Biol 2015 Apr;57(4):357-72

Plant Physiology Laboratory, Faculty of Biological and Environmental Sciences, University of León, E-24071 León, Spain; Centre for Plant Biotechnology and Genomics (CBGP), Politechnical University of Madrid, E-28223 Madrid, Spain.

Maize (Zea mays L.) suspension-cultured cells with up to 70% less cellulose were obtained by stepwise habituation to dichlobenil (DCB), a cellulose biosynthesis inhibitor. Cellulose deficiency was accompanied by marked changes in cell wall matrix polysaccharides and phenolics as revealed by Fourier transform infrared (FTIR) spectroscopy. Cell wall compositional analysis indicated that the cellulose-deficient cell walls showed an enhancement of highly branched and cross-linked arabinoxylans, as well as an increased content in ferulic acid, diferulates and p-coumaric acid, and the presence of a polymer that stained positive for phloroglucinol. In accordance with this, cellulose-deficient cell walls showed a fivefold increase in Klason-type lignin. Thioacidolysis/GC-MS analysis of cellulose-deficient cell walls indicated the presence of a lignin-like polymer with a Syringyl/Guaiacyl ratio of 1.45, which differed from the sensu stricto stress-related lignin that arose in response to short-term DCB-treatments. Gene expression analysis of these cells indicated an overexpression of genes specific for the biosynthesis of monolignol units of lignin. A study of stress signaling pathways revealed an overexpression of some of the jasmonate signaling pathway genes, which might trigger ectopic lignification in response to cell wall integrity disruptions. In summary, the structural plasticity of primary cell walls is proven, since a lignification process is possible in response to cellulose impoverishment.
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http://dx.doi.org/10.1111/jipb.12346DOI Listing
April 2015

Covalent cross-linking of cell-wall polysaccharides through esterified diferulates as a maize resistance mechanism against corn borers.

J Agric Food Chem 2015 Mar 19;63(8):2206-14. Epub 2015 Feb 19.

Grupo de Genética y Mejora de Maíz, Misión Biológica de Galicia, Consejo Superior de Investigaciones Científicas (CSIC) , Apartado 28, 36080 Pontevedra, Spain.

There is strong evidence to suggest that cross-linking of cell-wall polymers through ester-linked diferulates has a key role in plant resistance to pests; however, direct experimentation to provide conclusive proof is lacking. This study presents an evaluation of the damage caused by two corn borer species on six maize populations particularly selected for divergent diferulate concentrations in pith stem tissues. Maize populations selected for high total diferulate concentration had 31% higher diferulates than those selected for low diferulates. Stem tunneling by corn borer species was 29% greater in the population with the lowest diferulates than in the population with the highest diferulates (31.7 versus 22.6 cm), whereas total diferulate concentration was negatively correlated with stem tunneling by corn borers. Moreover, orthogonal contrasts between groups of populations evaluated showed that larvae fed in laboratory bioassays on pith stem tissues from maize populations with higher diferulates had 30-40% lower weight than larvae fed on the same tissues from maize populations with lower diferulates. This is the first report that shows a direct relationship between diferulate deposition in maize cell walls and corn borer resistance. Current findings will help to develop adapted maize varieties with an acceptable level of resistance against borers and be useful in special kinds of agriculture, such as organic farming.
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http://dx.doi.org/10.1021/jf505341dDOI Listing
March 2015

Critical environmental and genotypic factors for Fusarium verticillioides infection, fungal growth and fumonisin contamination in maize grown in northwestern Spain.

Int J Food Microbiol 2014 May 19;177:63-71. Epub 2014 Feb 19.

Misión Biológica de Galicia (CSIC), Apdo. 28, 36080 Pontevedra, Spain.

In northwestern Spain, where weather is rainy and mild throughout the year, Fusarium verticillioides is the most prevalent fungus in kernels and a significant risk of fumonisin contamination has been exposed. In this study, detailed information about environmental and maize genotypic factors affecting F. verticillioides infection, fungal growth and fumonisin content in maize kernels was obtained in order to establish control points to reduce fumonisin contamination. Evaluations were conducted in a total of 36 environments and factorial regression analyses were performed to determine the contribution of each factor to variability among environments, genotypes, and genotype × environment interactions for F. verticillioides infection, fungal growth and fumonisin content. Flowering and kernel drying were the most critical periods throughout the growing season for F. verticillioides infection and fumonisin contamination. Around flowering, wetter and cooler conditions limited F. verticillioides infection and growth, and high temperatures increased fumonisin contents. During kernel drying, increased damaged kernels favored fungal growth, and higher ear damage by corn borers and hard rainfall favored fumonisin accumulation. Later planting dates and especially earlier harvest dates reduced the risk of fumonisin contamination, possibly due to reduced incidence of insects and accumulation of rainfall during the kernel drying period. The use of maize varieties resistant to Sitotroga cerealella, with good husk coverage and non-excessive pericarp thickness could also be useful to reduce fumonisin contamination of maize kernels.
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http://dx.doi.org/10.1016/j.ijfoodmicro.2014.02.004DOI Listing
May 2014

Is it possible to control fumonisin contamination in maize kernels by using genotypes resistant to the Mediterranean corn borer?

J Econ Entomol 2013 Oct;106(5):2241-6

Misión Biológica de Galicia, Spanish Council for Scientific Research (CSIC), Apartado 28, E-36080 Pontevedra, Spain.

Insect activity has long been associated with Fusarium infection. The objectives of the current study were 1) to estimate the impact of Mediterranean corn borer, Sesamia nonagrioides Lefèbvre, damage on fumonisin contamination in the maize kernel by comparing fumonisin contamination under infestation and protected conditions, and 2) to measure the potential use of genotypes resistant to this borer as controlling factors of fumonisin contamination. Genotypes with increased kernel damage by borers tended to increase fumonisin accumulation under infestation conditions. In particular environments, other factors influenced fumonisin contamination more than damage by borers. When ear damage by borers is significant, maize resistance to ear damage could contribute to the reduction of fumonisin contamination in the kernels. Genotype such as EP42 x EP77 that combines low ear damage by borers and low fumonisin level across environments is a good choice to control fumonisin contamination. The use of an applicable methodology to identify Mediterranean corn borer-resistant genotypes to ear attack under artificial infestations might be a promising approach.
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http://dx.doi.org/10.1603/ec13084DOI Listing
October 2013

A genome-wide association study reveals genes associated with fusarium ear rot resistance in a maize core diversity panel.

G3 (Bethesda) 2013 Nov 6;3(11):2095-104. Epub 2013 Nov 6.

Department of Crop Science, North Carolina State University, Raleigh, North Carolina 27695.

Fusarium ear rot is a common disease of maize that affects food and feed quality globally. Resistance to the disease is highly quantitative, and maize breeders have difficulty incorporating polygenic resistance alleles from unadapted donor sources into elite breeding populations without having a negative impact on agronomic performance. Identification of specific allele variants contributing to improved resistance may be useful to breeders by allowing selection of resistance alleles in coupling phase linkage with favorable agronomic characteristics. We report the results of a genome-wide association study to detect allele variants associated with increased resistance to Fusarium ear rot in a maize core diversity panel of 267 inbred lines evaluated in two sets of environments. We performed association tests with 47,445 single-nucleotide polymorphisms (SNPs) while controlling for background genomic relationships with a mixed model and identified three marker loci significantly associated with disease resistance in at least one subset of environments. Each associated SNP locus had relatively small additive effects on disease resistance (±1.1% on a 0-100% scale), but nevertheless were associated with 3 to 12% of the genotypic variation within or across environment subsets. Two of three identified SNPs colocalized with genes that have been implicated with programmed cell death. An analysis of associated allele frequencies within the major maize subpopulations revealed enrichment for resistance alleles in the tropical/subtropical and popcorn subpopulations compared with other temperate breeding pools.
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http://dx.doi.org/10.1534/g3.113.007328DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3815068PMC
November 2013

Environmental factors related to fungal infection and fumonisin accumulation during the development and drying of white maize kernels.

Int J Food Microbiol 2013 Jun 23;164(1):15-22. Epub 2013 Mar 23.

Misión Biológica de Galicia (CSIC), Apdo. 28, 36080 Pontevedra, Spain.

In Southern Europe where whole maize kernels are ground and used for making bread and other food products, infection of the kernels by Fusarium verticillioides and subsequent fumonisin contamination pose a serious safety issue. The influence of environmental factors on this fungal infection and mycotoxin accumulation as the kernel develops has not been fully determined, especially in such food grade maize. The objectives of the present study were to determine which environmental factors may contribute to kernel invasion by F. verticillioides and fumonisin accumulation as kernels develop and dry in naturally infected white maize. Three maize hybrids were planted at two different sowing dates and kernel samples were collected 20, 40, 60, 80 and 100 days after silking. The percentage of kernels infected, and ergosterol and fumonisin contents were recorded for each sampling. F. verticillioides was the most prevalent species identified as the kernels developed. Temperature and moisture conditions during the first 80 days after silking favored natural kernel infection by F. verticillioides rather than by Aspergillus or Penicillium species. Fumonisin was found in kernels as early as 20 days after silking however significant fumonisin accumulation above levels acceptable in the EU did not occur until after physiological maturity of the kernel indicating that kernel drying in the field poses a high risk. Our results suggest that this could be due to increasing kernel damage by insects that favor fungal development, such as the damage by the moth Sitotroga cerealella, and to the occurrence of stress conditions for F. verticillioides growth that could trigger fumonisin biosynthesis, such as exposure to suboptimal temperatures for growth simultaneously with low water activity.
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http://dx.doi.org/10.1016/j.ijfoodmicro.2013.03.012DOI Listing
June 2013

Impact of cell wall composition on maize resistance to pests and diseases.

Int J Mol Sci 2013 Mar 27;14(4):6960-80. Epub 2013 Mar 27.

Misión Biológica de Galicia (CSIC), Pontevedra E-36080, Spain.

In cereals, the primary cell wall is built of a skeleton of cellulosic microfibrils embedded in a matrix of hemicelluloses and smaller amounts of pectins, glycoproteins and hydroxycinnamates. Later, during secondary wall development, p-coumaryl, coniferyl and sinapyl alcohols are copolymerized to form mixed lignins. Several of these cell wall components show a determinative role in maize resistance to pest and diseases. However, defense mechanisms are very complex and vary among the same plant species, different tissues or even the same tissue at different developmental stages. Thus, it is important to highlight that the role of the cell wall components needs to be tested in diverse genotypes and specific tissues where the feeding or attacking by the pathogen takes place. Understanding the role of cell wall constituents as defense mechanisms may allow modifications of crops to withstand pests and diseases.
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http://dx.doi.org/10.3390/ijms14046960DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3645672PMC
March 2013

Divergent selection for ester-linked diferulates in maize pith stalk tissues. Effects on cell wall composition and degradability.

Phytochemistry 2012 Nov 30;83:43-50. Epub 2012 Aug 30.

CSIC-Misión Biológica de Galicia, Grupo de Genética y Mejora de Maíz, Apartado 28, 36080 Pontevedra, Spain.

Cross-linking of grass cell wall components through diferulates (DFAs) has a marked impact on cell wall properties. However, results of genetic selection for DFA concentration have not been reported for any grass species. We report here the results of direct selection for ester-linked DFA concentration in maize stalk pith tissues and the associated changes in cell wall composition and biodegradability. After two cycles of divergent selection, maize populations selected for higher total DFA (DFAT) content (CHs) had 16% higher DFAT concentrations than populations selected for lower DFAT content (CLs). These significant DFA concentration gains suggest that DFA deposition in maize pith parenchyma cell walls is a highly heritable trait that is genetically regulated and can be modified trough conventional breeding. Maize populations selected for higher DFAT had 13% less glucose and 10% lower total cell wall concentration than CLs, suggesting that increased cross-linking of feruloylated arabinoxylans results in repacking of the matrix and possibly in thinner and firmer cell walls. Divergent selection affected esterified DFAT and monomeric ferulate ether cross link concentrations differently, supporting the hypothesis that the biosynthesis of these cell wall components are separately regulated. As expected, a more higher DFA ester cross-coupled arabinoxylan network had an effect on rumen cell wall degradability (CLs showed 12% higher 24-h total polysaccharide degradability than CHs). Interestingly, 8-8-coupled DFAs, previously associated with cell wall strength, were the best predictors of pith cell wall degradability (negative impact). Thus, further research on the involvement of these specific DFA regioisomers in limiting cell wall biodegradability is encouraged.
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http://dx.doi.org/10.1016/j.phytochem.2012.07.026DOI Listing
November 2012

Is the basal area of maize internodes involved in borer resistance?

BMC Plant Biol 2011 Oct 14;11:137. Epub 2011 Oct 14.

Misión Biológica de Galicia, Spanish National Research Council (CSIC), Apartado 28, 36080 Pontevedra, Spain.

Background: To elucidate the role of the length of the internode basal ring (LIBR) in resistance to the Mediterranean corn borer (MCB), we carried out a divergent selection program to modify the LIBR using two maize synthetic varieties (EPS20 and EPS21), each with a different genetic background. We investigated the biochemical mechanisms underlying the relationship between the LIBR and borer resistance. Selection to lengthen or shorten the LIBR was achieved for each synthetic variety. The resulting plants were analyzed to determine their LIBR response, growth, yield, and borer resistance.

Results: In the synthetic variety EPS20 (Reid germplasm), reduction of the LIBR improved resistance against the MCB. The LIBR selection was also effective in the synthetic variety EPS21 (non-Reid germplasm), although there was no relationship detected between the LIBR and MCB resistance. The LIBR did not show correlations with agronomic traits such as plant height and yield. Compared with upper sections, the internode basal ring area contained lower concentrations of cell wall components such as acid detergent fiber (ADF), acid detergent lignin (ADL), and diferulates. In addition, some residual 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3-(4H)-one (DIMBOA), a natural antibiotic compound, was detected in the basal area at 30 days after silking.

Conclusion: We analyzed maize selections to determine whether the basal area of maize internodes is involved in borer resistance. The structural reinforcement of the cell walls was the most significant trait in the relationship between the LIBR and borer resistance. Lower contents of ADF and ADL in the rind of the basal section facilitated the entry of larvae in this area in both synthetic varieties, while lower concentrations of diferulates in the pith basal section of EPS20 facilitated larval feeding inside the stem. The higher concentrations of DIMBOA may have contributed to the lack of correlation between the LIBR and borer resistance in EPS21. This novel trait could be useful in maize breeding programs to improve borer resistance.
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http://dx.doi.org/10.1186/1471-2229-11-137DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3206430PMC
October 2011

Inducible maize defense mechanisms against the corn borer Sesamia nonagrioides: a transcriptome and biochemical approach.

Mol Plant Microbe Interact 2012 Jan;25(1):61-8

Spanish Council for Scientific Research, Pontevedra, Spain.

In spite of multiple studies elucidating individual defense mechanisms against stalk borer feeding, little information is available about the plant response to these members of Lepidoptera. Four maize inbred lines were cultivated in a greenhouse and challenged with larvae of the corn borer Sesamia nonagrioides. Transcriptome and biochemical analyses were performed to elucidate the maize response mechanisms to this insect. General plant defense mechanisms were activated, including the jasmonic acid biosynthetic pathway, proteinase inhibitors, and four defense-related transcription factors. Interestingly, gene ontology analysis shows that maize plants undergo cell-wall reorganization after being attacked. These results were confirmed through biochemical analyses showing that the concentration of some cell-wall-related compounds significantly changed after plant infestation in a genotype-dependent way. In conclusion, maize plants respond to the attack of the corn borer S. nonagrioides through cell-wall fortification, activating genes involved in cell-wall organization, which finally is reflected in a higher concentration of some cell-wall components, especially in resistant genotypes.
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http://dx.doi.org/10.1094/MPMI-06-11-0154DOI Listing
January 2012

Role of hydroxycinnamic acids in the infection of maize silks by Fusarium graminearum Schwabe.

Mol Plant Microbe Interact 2011 Sep;24(9):1020-6

Spanish Council for Scientific Research, Pontevedra, Spain.

In the current study, the hydroxycinnamic acids in silks of diverse maize inbred lines differing in Fusarium resistance were determined at several times after inoculation with Fusarium graminearum or sterile water as control. The main objective was to determine the possible relationship between the hydroxycinnamic acid changes in silks and ear rot resistance. Several changes in the cell-wall-bound hydroxycinnamic acid concentrations were observed after inoculation with F. graminearum, although these changes were not directly correlated with genotypic resistance to this fungus. Ester-bound ferulic acid decreased, probably due to degradation of hemicellulose by hydrolytic enzymes produced by Fusarium spp., while p-coumaric acid and diferulates showed slight increases that, in conjunction, did not result in delayed F. graminearum progression through the silks. It is important to note that the decrease of ferulic acid in the F. graminearum treatment was faster in susceptible than in resistant genotypes, suggesting a differential hemicellulose degradation in silk tissues. Therefore, the ability of the maize genotypes to slow down that process through hemicellulose structural features or xylanase inhibitors needs to be addressed in future studies.
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http://dx.doi.org/10.1094/MPMI-03-11-0079DOI Listing
September 2011

Cell wall composition as a maize defense mechanism against corn borers.

Phytochemistry 2011 Apr 1;72(4-5):365-71. Epub 2011 Feb 1.

Misión Biológica de Galicia (CSIC), Apartado 28, E-36080 Pontevedra, Spain.

European and Mediterranean corn borers are two of the most economically important insect pests of maize (Zea mays L.) in North America and southern Europe, respectively. Cell wall structure and composition were evaluated in pith and rind tissues of resistant and susceptible inbred lines as possible corn borer resistance traits. Composition of cell wall polysaccharides, lignin concentration and composition, and cell wall bound forms of hydroxycinnamic acids were measured. As expected, most of the cell wall components were found at higher concentrations in the rind than in the pith tissues, with the exception of galactose and total diferulate esters. Pith of resistant inbred lines had significantly higher concentrations of total cell wall material than susceptible inbred lines, indicating that the thickness of cell walls could be the initial barrier against corn borer larvae attack. Higher concentrations of cell wall xylose and 8-O-4-coupled diferulate were found in resistant inbreds. Stem tunneling by corn borers was negatively correlated with concentrations of total diferulates, 8-5-diferulate and p-coumarate esters. Higher total cell wall, xylose, and 8-coupled diferulates concentrations appear to be possible mechanisms of corn borer resistance.
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http://dx.doi.org/10.1016/j.phytochem.2011.01.004DOI Listing
April 2011

Role of dehydrodiferulates in maize resistance to pests and diseases.

Int J Mol Sci 2010 Feb 9;11(2):691-703. Epub 2010 Feb 9.

Misión Biológica de Galicia, CSIC, Pontevedra, Spain.

Phenolic esters have attracted considerable interest due to the potential they offer for peroxidase catalysed cross-linking of cell wall polysaccharides. Particularly, feruloyl residues undergo radical coupling reactions that result in cross-linking (intra-/intermolecular) between polysaccharides, between polysaccharides and lignin and, between polysaccharides and proteins. This review addresses for the first time different studies in which it is established that cross-linking by dehydrodiferulates contributes to maize's defences to pests and diseases. Dehydrodiferulate cross-links are involved in maize defence mechanisms against insects such as the European, Mediterranean, and tropical corn borers and, storage pest as the maize weevil. In addition, cross-links are also discussed to be involved in genetic resistance of maize to fungus diseases as Gibberella ear and stalk rot. Resistance against insects and fungus attending dehydrodiferulates could go hand in hand. Quantitative trait loci mapping for these cell wall components could be a useful tool for enhancing resistance to pest and diseases in future breeding programs.
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http://dx.doi.org/10.3390/ijms11020691DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2852861PMC
February 2010

QTL mapping for Mediterranean corn borer resistance in European flint germplasm using recombinant inbred lines.

BMC Genomics 2010 Mar 15;11:174. Epub 2010 Mar 15.

Misión Biológica de Galicia, Spanish National Research Council (CSIC), Apartado 28, 36080 Pontevedra, Spain.

Background: Ostrinia nubilalis (ECB) and Sesamia nonagrioides (MCB) are two maize stem borers which cause important losses in temperate maize production, but QTL analyses for corn borer resistance were mostly restricted to ECB resistance and maize materials genetically related (mapping populations derived from B73). Therefore, the objective of this work was to identify and characterize QTLs for MCB resistance and agronomic traits in a RILs population derived from European flint inbreds.

Results: Three QTLs were detected for stalk tunnel length at bins 1.02, 3.05 and 8.05 which explained 7.5% of the RILs genotypic variance. The QTL at bin 3.05 was co-located to a QTL related to plant height and grain humidity and the QTL at bin 8.05 was located near a QTL related to yield.

Conclusions: Our results, when compared with results from other authors, suggest the presence of genes involved in cell wall biosynthesis or fortification with effects on resistance to different corn borer species and digestibility for dairy cattle. Particularly, we proposed five candidate genes related to cell wall characteristics which could explain the QTL for stalk tunnelling in the region 3.05. However, the small proportion of genotypic variance explained by the QTLs suggest that there are also many other genes of small effect regulating MCB resistance and we conclude that MAS seems not promising for this trait. Two QTLs detected for stalk tunnelling overlap with QTLs for agronomic traits, indicating the presence of pleitropism or linkage between genes affecting resistance and agronomic traits.
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http://dx.doi.org/10.1186/1471-2164-11-174DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2841681PMC
March 2010

Mapping of QTL for resistance to the Mediterranean corn borer attack using the intermated B73 x Mo17 (IBM) population of maize.

Theor Appl Genet 2009 Nov 16;119(8):1451-9. Epub 2009 Sep 16.

Misión Biológica de Galicia, Spanish National Research Council (CSIC), 36080, Apartado 28, Pontevedra, Spain.

The Mediterranean corn borer or pink stem borer (MCB, Sesamia nonagrioides Lefebvre) causes important yield losses as a consequence of stalk tunneling and direct kernel damage. B73 and Mo17 are the source of the most commercial valuable maize inbred lines in temperate zones, while the intermated B73 x Mo17 (IBM) population is an invaluable source for QTL identification. However, no or few experiments have been carried out to detect QTL for corn borer resistance in the B73 x Mo17 population. The objective of this work was to locate QTL for resistance to stem tunneling and kernel damage by MCB in the IBM population. We detected a QTL for kernel damage at bin 8.05, although the effect was small and two QTL for stalk tunneling at bins 1.06 and 9.04 in which the additive effects were 4 cm, approximately. The two QTL detected for MCB resistance were close to other QTL consistently found for European corn borer (ECB, Ostrinia nubilalis Hübner) resistance, indicating mechanisms of resistance common to both pests or gene clusters controlling resistance to different plagues. The precise mapping achieved with the IBM population will facilitate the QTL pyramiding and the positional cloning of the detected QTL.
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http://dx.doi.org/10.1007/s00122-009-1147-6DOI Listing
November 2009

Changes in phenolic concentrations during recurrent selection for resistance to the Mediterranean corn borer (Sesamia nonagrioides Lef.).

J Agric Food Chem 2008 Sep 26;56(17):8017-22. Epub 2008 Jul 26.

Misión Biológica de Galicia, Spanish Council for Scientific Research (CSIC), Apartado 28, E-36080 Pontevedra, Spain.

Recurrent selection has been reported as successful for improving maize resistance against corn borers. This study was conducted to determine if phenolics concentration in maize changes during recurrent selection to improve stalk resistance to the Mediterranean corn borer. Three cycles of selection [EPS12(S)C0, ESP12(S)C2, and EPS12(S)C3] from the maize synthetic population EPS12 and test crosses to inbred lines A639, B93, and EP42 were field grown and artificially infested with Mediterranean corn borer larvae, and the pith tissues were sampled for biochemical analyses. Two major simple phenolic acids [p-coumaric (p-CA) and trans-ferulic (E-FA) acids] were identified in free and cell-wall fractions, whereas four isomers of diferulic acid (DFA) (8-5'l, 5-5', 8-o-4', and 8-5' benzofuran form) were present in the cell-wall bound fraction. The selection cycles EPS12(S)C0 and EPS12(S)C3 showed less damage and higher cell wall phenolics concentrations than the cycle EPS12(S)C2. In addition, higher concentrations of total DFAs were associated with shorter tunnel length and lower numbers of larvae per stem. The current study shows new and concrete evidence that the cell-wall bound phenolics could have a determinative role in the resistance to the Mediterranean corn borer, although future development of recurrent and divergent selection cycles will clarify this point.
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http://dx.doi.org/10.1021/jf800922jDOI Listing
September 2008