Seed germination and seedling establishment are important for the reproductive success of plants, but seeds and seedlings typically encounter constantly changing environmental conditions. By inhibiting seed germination and post-germinative growth through the PYR1/PYL/RCAR ABA receptors and PP2C co-receptors, the phytohormone abscisic acid (ABA) prevents premature germination and seedling growth under unfavorable conditions. However, little is known about how the ABA-mediated inhibition of seed germination and seedling establishment is thwarted. Here, we report that ABA Signaling Terminator (ABT), a WD40 protein, efficiently switches off ABA signaling and is critical for seed germination and seedling establishment. ABT is induced by ABA in a PYR1/PYL/RCAR-PP2C-dependent manner. Overexpression of ABT promotes seed germination and seedling greening in the presence of ABA, whereas knockout of ABT has the opposite effect. We found that ABT interacts with the PYR1/PYL/RCAR and PP2C proteins, interferes with the interaction between PYR1/PYL4 and ABI1/ABI2, and hampers the inhibition of ABI1/ABI2 by ABA-bound PYR1/PYL4, thereby terminating ABA signaling. Taken together, our results reveal a core mechanism of ABA signaling termination that is critical for seed germination and seedling establishment in Arabidopsis.

种子的发芽和幼苗的生长对于植物的繁殖成功很重要，但是种子和幼苗通常会遇到不断变化的环境条件。通过抑制PYR1 / PYL / RCAR ABA受体和PP2C辅助受体的种子发芽和发芽后生长，植物激素脱落酸（ABA）可防止不利条件下的过早发芽和幼苗生长。但是，关于如何阻止ABA介导的种子萌发和幼苗生长的抑制作用知之甚少。在这里，我们报道ABA信号终止子（ABT），一种WD40蛋白，有效地关闭了ABA信号，对于种子发芽和幼苗的建立至关重要。ABA以PYR1 / PYL / RCAR-PP2C依赖性方式诱导ABT。过度表达在ABA存在下，ABT促进种子发芽和幼苗绿化，而敲除ABT具有相反的作用。我们发现，ABT与PYR1 / PYL / RCAR和PP2C蛋白相互作用，干扰PYR1 / PYL4和ABI1 / ABI2之间的相互作用，并阻碍ABA结合的PYR1 / PYL4对ABI1 / ABI2的抑制，从而终止ABA信号传导。综上所述，我们的结果揭示了ABA信号传导终止的核心机制，该机制对于拟南芥种子的萌发和幼苗的建立至关重要。