Stigmatic papilla cells secrete jasmonic acid to promote pollen germination through calcium signaling

levels in pollen grains. We found that pollen grains exhibited significantly slower germination in vitro than on stigmas, and that exogenous JA supplementation rescued this in vitro germination defect. We further showed that stigmatic papilla cells accumulated high concentrations of JA, which was secreted to promote pollen germination. Disruption of essential genes for JA synthesis, rather than the JA receptor COI1 in the stigma, causes defective pollen germination. JA triggers calcium elevation in pollen grains, and this elevated calcium signal is required for pollen germination and can be suppressed by calcium channel inhibitors. We found that Annexin 1 and Annexin 2, two calcium channels expressed in pollen grains, contribute to JA-triggered calcium increase in pollen grains. Consistently, applying JA on the stigma could promote interspecific pollen germination. In summary, our work identifies a new role for stigma-derived JA in promoting pollen germination by triggering calcium signaling in pollen grains.