Ethylene negatively mediates self-incompatibility response in Brassica rapa.

Self-incompatibility (SI) is a genetic mechanism most flowering plants adopted to reject self-pollen thus avoid inbreeding. In the Brassicaceae, self-pollen recognition triggers downstream signaling pathways to reject self-pollen. However, the downstream signaling pathways are not very clear. Here we show that ethylene negatively mediates self-incompatibility response of Chinese cabbage (Brassica rapa L. ssp. Pekinensis) via PCD in papilla cells. We found that ethylene signaling genes were upregulated after cross-pollination. Treating stigmas with ethylene, or suppressing the expression of a negative regulator of ethylene signaling, CONSTITUTIVE TRIPLE RESPONSE 1 (CTR1), caused PCD in papilla cells and broke down the self-incompatibility. On the other hand, treating stigmas with ethylene inhibitors, or suppressing the expression of ethylene-responsive factors (ERFs), inhibited PCD in papilla cells and the compatible pollination. Our study identified an additional signaling pathway mediating self-incompatibility responses in the Brassicaceae and also developed a new method in overcoming self-incompatibility to improve the efficiency of inbred line propagation in agriculture practice.