Brassinosteroids synthesised by CYP85A/A1 but not CYP85A2 function via a BRI1-like receptor but not via BRI1 in Picea abies. (28th November 2020)

• Record Type: Journal Article
• Authors: Wang, Li; Liu, Jing; Shen, Yitong; Pu, Ruolan; Hou, Meiying; Wei, Qiang; Zhang, Xinzhen; Li, Guishuang; Ren, Hongyan; Wu, Guang
• Editors: Murray, James
• Is Part Of: Journal of experimental botany. Volume 72:Number 5(2021)
• Page Start: 1748
• Page End: 1763
• Publication Date: 2020-11-28
• Subjects: Brassinosteroid -- gymnosperms -- Norway spruce -- Picea abies -- plant evolution -- plant development -- plant hormones -- plant steroids -- receptor function -- signaling pathway; Botany -- Periodicals; Botany, Experimental -- Periodicals; Plant physiology -- Periodicals; 580
• DOI: 10.1093/jxb/eraa557
• Languages: English
• ISSNs: 0022-0957

Abstract

Abstract : Picea abies lacks the most active brassinosteroid (BR) receptor BRI1 and the biosynthesis enzymes for the most active BR, brassinolide, but it does possess a weak but active BR response through castasterone and BRI1-like receptors. Abstract: Brassinosteroids (BRs) are essential plant hormones. In angiosperms, brassinolide and castasterone, the first and second most active BRs, respectively, are synthesised by CYP85A2 and CYP85A/A1, respectively. BRs in angiosperms function through an essential receptor, BR Insensitive 1 (BRI1). In addition, some angiosperms also have non-essential BRI1-like 1/3 (BRL1/3). In conifers, BRs promote seed germination under drought stress; however, how BRs function in gymnosperms is unknown. In this study, we performed functional complementation of BR biosynthesis and receptor genes from Picea abies with respective Arabidopsis mutants. We found that P. abies possessed functional PaCYP85A and PaBRL1 but not PaCYP85A2 or PaBRI1, and this results in weak BR signaling, and both PaCYP85A and PaBRL1 were abundantly expressed. However, neither BR treatment of P. abies seedlings nor expression of PaBRL1 in the Arabidopsis Atbri1 mutant promoted plant height, despite the fact that BR-responsive genes were activated. Importantly, chimeric AtBRI1 replaced with the BR-binding domain of PaBRL1 complemented the Atbri1 phenotypes. Furthermore, PaBRL1 had less kinase activity than BRI1 in vitro . Overall, P. abies had weak but still active BR signaling, explaining aspects of its slow growth and high stress tolerance. Our study sheds light on the functional and evolutionary significance of distinct BR signaling that is independent of BRI1 and brassinolide.