In angiosperms, the process of pollination relies on species-specific interaction and signaling between the male (pollen) and female (pistil) counterparts where the interplay between several pollen and stigma proteins decides the fate of the pollen. In Brassicaceae, the dry stigmatic papillary cells control pollen germination by releasing resources only to compatible pollen thereby allowing pollen to hydrate and germinate. Despite the identification of a number of stigmatic proteins that facilitate pollination responses, the signaling mechanisms that regulate functions of these proteins have remained unknown. Here, we show that, in Arabidopsis, an extremely functionally redundant mitogen-activated protein kinase (MAPK) cascade is required for maintaining stigma receptivity to accept compatible pollen. Our genetic analyses demonstrate that in stigmas, five MAPK kinases (MKKs), MKK1/2/3/7/9 are required to transmit upstream signals to two MPKs, MPK3/4, to mediate compatible pollination. Compromised functions of these five MKKs in the quintuple mutant (mkk1/2/3RNAi/mkk7/9) phenocopied pollination defects observed in the mpk4RNAi/mpk3 double mutant. We further show that this MAPK nexus converges on Exo70A1, a previously identified stigma receptivity factor essential for pollination. Given that pollination is the crucial initial step during plant reproduction, understanding the mechanisms that govern successful pollination could lead to development of strategies to improve crop yield.

在被子植物中，授粉过程依赖于雄性（花粉）和雌性（雌蕊）对应物之间的物种特异性相互作用和信号传导，其中几种花粉和柱头蛋白之间的相互作用决定了花粉的命运。在十字花科中，干燥的有斑点的乳头状细胞通过仅向相容的花粉释放资源来控制花粉的萌发，从而使花粉水合并发芽。尽管已鉴定出许多有助于授粉反应的带象质的蛋白质，但调节这些蛋白质功能的信号传导机制仍然未知。在这里，我们证明了在拟南芥中，需要极高功能的丝裂原活化蛋白激酶（MAPK）级联来维持柱头接受性，以接受相容的花粉。我们的遗传分析表明，在柱头中，需要五个MAPK激酶（MKK）MKK1 / 2/3/7/9才能将上游信号传输至两个MPK MPK3 / 4，以介导相容的授粉。这五个的受损功能MKKs在五元组突变体（MKK1 / 2 / 3RNAi / MKK7 / 9）中所观察到的表型模拟授粉缺陷mpk4RNAi / MPK3双突变体。我们进一步表明，该MAPK链接在Exo70A1上收敛，Exo70A1是先前确定的对授粉必不可少的柱头接受因子。鉴于授粉是植物繁殖过程中至关重要的初始步骤，因此了解成功控制授粉的机制可能会导致制定提高作物产量的策略。