Jahan Akida, Yamazaki Yuto, Islam Mousona, Ghosh Totan Kumar, Yoshimura Nami, Kato Hirotaka, Ishizaki Kimitsune, Shinozawa Akihisa, Sakata Yoichi, Takezawa Daisuke
Graduate School of Science and Engineering, Saitama University, Saitama, Japan.
Biological Research Division, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh.
Front Plant Sci. 2022 Jul 28;13:952820. doi: 10.3389/fpls.2022.952820. eCollection 2022.
Phytohormone abscisic acid (ABA) plays a key role in stomata closure, osmostress acclimation, and vegetative and embryonic dormancy. Group B3 Raf protein kinases (B3-Rafs) serve as positive regulators of ABA and osmostress signaling in the moss and the angiosperm . While has a single B3-Raf called ARK, specific members of B3-Rafs among six paralogs regulate ABA and osmostress signaling in , indicating functional diversification of B3-Rafs in angiosperms. However, we found that the liverwort , belonging to another class of bryophytes, has three paralogs of B3-Rafs, Mp, Mp, and Mp, with structural variations in the regulatory domains of the polypeptides. By reporter assays of the line and analysis of genome-editing lines of , we found that these B3-Rafs are functionally redundant in ABA response, with respect to inhibition of growth, tolerance to desiccation and expression of stress-associated transcripts, the majority of which are under the control of the PYR/PYL/RCAR-like receptor Mp. Interestingly, gemmae in gemma cups were germinating only in mutant lines associated with Mp, indicating that dormancy in the gametophyte is controlled by a specific B3-Raf paralog. These results indicated not only conservation of the role of B3-Rafs in ABA and osmostress response in liverworts but also functional diversification of B3-Rafs, which is likely to have occurred in the early stages of land plant evolution.
植物激素脱落酸（ABA）在气孔关闭、渗透胁迫适应以及营养和胚胎休眠中起关键作用。B3组Raf蛋白激酶（B3-Rafs）在苔藓植物和被子植物中作为ABA和渗透胁迫信号的正调控因子。虽然苔藓植物只有一种名为ARK的B3-Raf，但六个旁系同源物中的特定B3-Raf成员在被子植物中调节ABA和渗透胁迫信号，这表明B3-Rafs在被子植物中功能多样化。然而，我们发现属于另一类苔藓植物的地钱有三种B3-Raf的旁系同源物，即Mp、Mp和Mp，其多肽调控结构域存在结构变异。通过对该品系的报告基因检测和对地钱基因组编辑品系的分析，我们发现这些B3-Rafs在ABA反应中功能冗余，在生长抑制、耐干燥性和胁迫相关转录本表达方面，其中大多数受PYR/PYL/RCAR样受体Mp的控制。有趣的是，只有与Mp相关的突变品系中的叶状体杯中的芽孢才会萌发，这表明配子体中的休眠受特定的B3-Raf旁系同源物控制。这些结果不仅表明B3-Rafs在地钱的ABA和渗透胁迫反应中的作用具有保守性，而且还表明B3-Rafs功能多样化，这可能发生在陆地植物进化的早期阶段。
