A gamma-thionin protein from apple, MdD1, is required for defence against S-RNase-induced inhibition of pollen tube prior to self/non-self recognition.

Plant Biotechnol J 2019 Apr 18. Epub 2019 Apr 18.

Laboratory of Fruit Cell and Molecular Breeding, China Agricultural University, Beijing, China.

Apple exhibits S-RNase-mediated self-incompatibility. Although the cytotoxic effect of S-RNase inside the self-pollen tube has been studied extensively, the underlying defence mechanism in pollen tube in Rosaceae remains unclear. On exposure to stylar S-RNase, plant defence responses are activated in the pollen tube; however, how these are regulated is currently poorly understood. Here, we show that entry of both self and non-self S-RNase into pollen tubes of apple (Malus domestica) stimulates jasmonic acid (JA) production, in turn inducing the accumulation of MdMYC2 transcripts, a transcription factor in the JA signalling pathway widely considered to be involved in plant defence processes. MdMYC2 acts as a positive regulator in the pollen tube activating expression of MdD1, a gene encoding a defence protein. Importantly, MdD1 was shown to bind to the RNase activity sites of S-RNase leading to inhibition of enzymatic activity. This work provides intriguing insights into an ancient defence mechanism present in apple pollen tubes where MdD1 likely acts as a primary line of defence to inhibit S-RNase cytotoxicity prior to self/non-self recognition.

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http://dx.doi.org/10.1111/pbi.13131DOI Listing

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April 2019
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References

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Microbiology and Immunology Principles of Microbiology and Immunology
Davis B.D. et al.
BioScience 1969

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