Self-incompatibility in the Brassicaceae is controlled by multiple haplotypes encoding the pollen ligand (S-locus protein 11, SP11, also known as S-locus cysteine-rich protein, SCR) and its stigmatic receptor (S-receptor kinase, SRK). A haplotype-specific interaction between SP11/SCR and SRK triggers the self-incompatibility response that leads to self-pollen rejection, but the signalling pathway remains largely unknown. Here we show that Ca2+ influx into stigma papilla cells mediates self-incompatibility signalling. Using self-incompatible Arabidopsis thaliana expressing SP11/SCR and SRK, we found that self-pollination specifically induced an increase in cytoplasmic Ca2+ ([Ca2+]cyt) in papilla cells. Direct application of SP11/SCR to the papilla cell protoplasts induced Ca2+ increase, which was inhibited by D-(−)-2-amino-5-phosphonopentanoic acid (AP-5), a glutamate receptor channel blocker. An artificial increase in [Ca2+]cyt in papilla cells arrested wild-type (WT) pollen hydration. Treatment of papilla cells with AP-5 interfered with self-incompatibility, and Ca2+ increase on the self-incompatibility response was reduced in the glutamate receptor-like channel (GLR) gene mutants. These results suggest that Ca2+ influx mediated by GLR is the essential self-incompatibility response leading to self-pollen rejection.
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We thank Y. Ryokume, M. Okamura, F. Yamamoto, and M. Matsumura-Kawashima for their technical assistance. This work was supported in part by Grants-in-Aid for Scientific Research on Innovative Areas (21112003 to M. Iwano; 23113002 to S.T.), Grants-in-Aid for Scientific Research (23570056, 26440145 to M. Iwano; 21248014, 25252021 to S.T.), and Grants-in-Aid for Creative Scientific Research (16GS0316 to A.I.) from the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT); and by Grants-in-Aid for JSPS Research Fellow (12J08273 to K.I.) from the Japan Society for the Promotion of Science (JSPS).
The authors declare no competing financial interests.
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Iwano, M., Ito, K., Fujii, S. et al. Calcium signalling mediates self-incompatibility response in the Brassicaceae. Nature Plants 1, 15128 (2015). https://doi.org/10.1038/nplants.2015.128
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