The control of seed dormancy by abscisic acid (ABA) has been extensively studied, but the underlying mechanism is not fully understood. Here, we report the characterization of two ABA-related seed dormancy regulators in Arabidopsis (Arabidopsis thaliana): ODR1 (for reversal of rdo5), an ortholog of the rice (Oryza sativa) Seed dormancy4 (Sdr4), and the basic helix-loop-helix transcription factor bHLH57. ODR1, whose transcript levels are directly suppressed by the transcription factor ABA INSENSITIVE3 (ABI3), negatively regulates seed dormancy by affecting ABA biosynthesis and ABA signaling. By contrast, bHLH57 positively regulates seed dormancy by inducing the expression of the genes 9-CIS-EPOXYCAROTENOID DIOXYGENASE6 (NCED6) and NCED9, which encode ABA biosynthetic enzymes, and thus leads to higher ABA levels. ODR1 interacts with bHLH57 and inhibits bHLH57-modulated NCED6 and NCED9 expression in the nucleus. bhlh57 loss-of-function alleles can partially counteract the enhanced NCED6 and NCED9 expression seen in odr1 mutants and can therefore rescue their associated hyper-dormancy phenotype. Thus, we identified a novel ABI3-ODR1-bHLH57-NCED6/9 network that provides insights into the regulation of seed dormancy by ABA biosynthesis and signaling.

脱落酸（ABA）对种子休眠的控制已得到广泛研究，但其潜在机理尚未完全明了。在这里，我们报道了拟南芥（Arabidopsis thaliana）中两个与ABA相关的种子休眠调节剂的特征：ODR1（用于逆转rdo5），水稻的直系同源物（Oryza sativa）种子休眠4（Sdr4）和基本螺旋环-螺旋转录因子bHLH57。ODR1的转录水平受到转录因子ABA INSENSITIVE3（ABI3）的直接抑制，它通过影响ABA的生物合成和ABA信号传导来负调节种子休眠。相比之下，bHLH57通过诱导9-CIS-EPOXYCAROTENOIDDIOXYGENASE6基因的表达来积极调节种子休眠（NCED6）和NCED9，它们编码ABA生物合成酶，因此导致较高的ABA水平。ODR1与bHLH57相互作用并抑制bHLH57调节的NCED6和NCED9在细胞核中的表达。bhlh57功能丧失的等位基因可以部分抵消在odr1突变体中看到的增强的NCED6和NCED9表达，因此可以挽救其相关的超休眠表型。因此，我们确定了一个新颖的ABI3-ODR1-bHLH57-NCED6 / 9网络，该网络提供了通过ABA生物合成和信号传导调节种子休眠的见解。