Most plants in the Brassicaceae evolve self-incompatibility (SI) to avoid inbreeding and generate hybrid vigor. Self-pollen is recognized by the S-haplotype-specific interaction of the pollen ligand S-locus protein 11 (SP11) (also known as S-locus cysteine-rich protein [SCR]) and its stigma-specific S-locus receptor kinase (SRK). However, mechanistically much remains unknown about the signaling events that culminate in self-pollen rejection. Here, we show that self-pollen triggers high levels of reactive oxygen species (ROS) in stigma papilla cells to mediate SI in heading Chinese cabbage (Brassica rapa L. ssp. pekinensis). We found that stigmatic ROS increased after self-pollination but decreased after compatible(CP)- pollination. Reducing stigmatic ROS by scavengers or suppressing the expression of respiratory burst oxidase homologs (Rbohs), which encode plant NADPH oxidases that produce ROS, both broke down SI. On the other hand, increasing the level of ROS inhibited the germination and penetration of compatible pollen on the stigma, mimicking an incompatible response. Furthermore, suppressing a B. rapa FERONIA (FER) receptor kinase homolog or Rac/Rop guanosine triphosphatase (GTPase) signaling effectively reduced stigmatic ROS and interfered with SI. Our results suggest that FER-Rac/Rop signaling-regulated, NADPH oxidase-produced ROS is an essential SI response leading to self-pollen rejection.

十字花科中的大多数植物都进化出自交不亲和性 (SI) 以避免近亲繁殖并产生杂种活力。自花粉通过花粉配体 S-基因座蛋白 11 (SP11)（也称为 S-基因座富含半胱氨酸蛋白 [SCR]）及其柱头特异性 S-基因座受体激酶的 S-单倍型特异性相互作用来识别（SRK）。然而，关于导致自花粉排斥的信号事件在机制上仍有很多未知。在这里，我们表明自花粉在柱头乳头细胞中触发高水平的活性氧 (ROS)，以介导大白菜 ( Brassica rapa L. ssp. pekinensis ) 的 SI）。我们发现柱头ROS在自花授粉后增加，但在相容（CP）-授粉后减少。通过清除剂减少柱头 ROS 或抑制呼吸爆发氧化酶同源物 (Rbohs) 的表达，它们编码产生 ROS 的植物 NADPH 氧化酶，都可以破坏 SI。另一方面，增加 ROS 水平会抑制相容花粉在柱头上的萌发和渗透，模仿不相容的反应。此外，抑制B. rapa FERONIA (FER) 受体激酶同源物或 Rac/Rop 鸟苷三磷酸酶 (GTPase) 信号传导可有效减少柱头 ROS 并干扰 SI。我们的研究结果表明，FER-Rac/Rop 信号调节、NADPH 氧化酶产生的 ROS 是导致自花粉排斥的必要 SI 反应。