Analysis of signal transduction induced by compatible signals in the Brassicaceae

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In the Brassicaceae, intraspecific non-self pollen (compatible pollen) can germinate and grow into stigmatic papilla cells, while self pollen or interspecific pollen is rejected at this stage. However, the mechanisms underlying this selective acceptance of compatible pollen remain unclear. Here, using a cell-impermeant calcium indicator, we showed that the compatible pollen coat contains signaling molecule(s) that stimulate Ca2+ export from the papilla cells. Transcriptome analyses of stigmas suggested that autoinhibited Ca2+-ATPase 13 (ACA13) was induced after both compatible pollination and compatible pollen coat treatment. ACA13 protein localized to the plasma membrane. The stigma of a T-DNA insertion line of ACA13 exhibited reduced Ca2+ export, as well as defects in compatible pollen germination and seed production. These findings suggest that stigmatic ACA13 functions in the export of Ca2+ to the compatible pollen tube, which promotes successful fertilization.