Nonogaki Hiroyuki
Department of Horticulture, Oregon State University, Corvallis, OR, USA.
J Exp Bot. 2020 May 30;71(10):2847-2853. doi: 10.1093/jxb/eraa062.
Seed dormancy is induced primarily by abscisic acid (ABA) and maintained through elevated levels of ABA sensitivity in seeds. The core mechanisms of ABA-imposed seed dormancy are emerging, but it is still unclear how these blockages in seeds are eliminated during after-ripening, or what molecular events in imbibed seeds are responsible for the initial stages of germination induction. Some pieces of evidence suggest that a repressor complex, which potentially triggers seed germination through the suppression of ABA signaling components, might be present in seeds. The usual suspect, protein phosphatase 2C, which inactivates kinases and shuts down ABA signaling in the major dormancy pathway, is possibly associated with this complex. Other members, such as WD40 proteins and histone deacetylase subunits, homologs of which are found in the flowering repressor complex, perhaps constitute this complex in seeds. The repressor activity could counteract the dormancy mechanisms in an overwhelming manner, through well-coordinated inactivation and turnover of germination-suppressing transcription factors, which is probably accompanied by chromatin silencing and transcriptional repression of the transcription factor target genes. This review provides a perspective on a putative seed germination-inducing repressor complex, including its possible modes of action and upstream regulators.
种子休眠主要由脱落酸（ABA）诱导，并通过种子中ABA敏感性的升高得以维持。ABA导致种子休眠的核心机制正在逐渐明晰，但仍不清楚这些种子休眠障碍在种子后熟过程中是如何消除的，也不清楚吸胀种子中的哪些分子事件负责萌发诱导的初始阶段。一些证据表明，种子中可能存在一种阻遏物复合体，它可能通过抑制ABA信号成分来触发种子萌发。常见的嫌疑蛋白磷酸酶2C可能与该复合体有关，它能使激酶失活并关闭主要休眠途径中的ABA信号。其他成员，如WD40蛋白和组蛋白去乙酰化酶亚基，其同源物存在于开花阻遏物复合体中，可能在种子中构成了这个复合体。阻遏物活性可能通过协调抑制萌发的转录因子的失活和周转，以压倒性的方式抵消休眠机制，这可能伴随着染色质沉默和转录因子靶基因的转录抑制。本文综述了一种假定的种子萌发诱导阻遏物复合体，包括其可能的作用模式和上游调节因子。
