Linden Katrina J, Hsia Mon Mandy, Chen Yi-Tze, Callis Judy
Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, United States.
Integrated Genetics and Genomics Graduate Program, University of California, Davis, Davis, CA, United States.
Front Plant Sci. 2021 Mar 16;12:641849. doi: 10.3389/fpls.2021.641849. eCollection 2021.
The ubiquitin system is essential for multiple hormone signaling pathways in plants. Here, we show that the E3 ligase BRIZ, a heteromeric ligase that consists minimally of BRIZ1 and BRIZ2 proteins, functions in abscisic acid (ABA) signaling or response. and homozygous mutants either fail to germinate or emerge later than wild-type seedlings, with little cotyledon expansion or root elongation and no visible greening. Viability staining indicates that and embryos are alive but growth-arrested. Germination of mutants is improved by addition of the carotenoid biosynthetic inhibitor fluridone or gibberellic acid (GA), and mutants have improved development in backgrounds deficient in ABA synthesis () or signaling (). Endogenous ABA is not higher in seeds compared to wild-type seeds, and exogenous ABA does not affect mRNAs in imbibed seeds. These results indicate that embryos are hypersensitive to ABA and that under normal growth conditions, BRIZ acts to suppress ABA signaling or response. ABA signaling and sugar signaling are linked, and we found that and mutants excised from seed coats are hypersensitive to sucrose. Although single mutants do not grow to maturity, we were able to generate mature double mutant plants that produced seeds. These seeds are more sensitive to exogenous sugar and are larger than seeds from sibling plants, suggesting that BRIZ has a parental effect on seed development. From these data, we propose a model in which the BRIZ E3 ligase suppresses ABA responses during seed maturation and germination and early seedling establishment.
泛素系统对植物中的多种激素信号通路至关重要。在此，我们表明E3连接酶BRIZ是一种异源连接酶，至少由BRIZ1和BRIZ2蛋白组成，在脱落酸（ABA）信号传导或响应中发挥作用。纯合突变体要么无法发芽，要么比野生型幼苗出苗晚，子叶几乎不扩展，根伸长也很少，且没有明显的变绿现象。活力染色表明突变体胚胎是活的，但生长停滞。添加类胡萝卜素生物合成抑制剂氟啶酮或赤霉素（GA）可改善突变体的发芽情况，并且在ABA合成（）或信号传导（）缺陷的背景下，突变体的发育得到改善。与野生型种子相比，突变体种子中的内源ABA并不更高，外源ABA也不影响吸胀种子中的mRNA。这些结果表明突变体胚胎对ABA高度敏感，并且在正常生长条件下，BRIZ起到抑制ABA信号传导或响应的作用。ABA信号传导和糖信号传导是相关联的，我们发现从种皮中分离出的突变体对蔗糖高度敏感。尽管单突变体无法生长至成熟，但我们能够培育出产生种子的成熟双突变体植株。这些种子对外源糖更敏感，且比同株双突变体植株的种子更大，这表明BRIZ对种子发育具有亲本表型效应。基于这些数据，我们提出了一个模型，其中BRIZ E3连接酶在种子成熟、萌发和幼苗早期建立过程中抑制ABA反应。
