Shigeta Tomoaki, Zaizen Yuichi, Asami Tadao, Yoshida Shigeo, Nakamura Yasushi, Okamoto Shigehisa, Matsuo Tomoaki, Sugimoto Yasushi
The United Graduate School of Agricultural Sciences, Kagoshima University, 1-21-24 Korimoto, Kagoshima, 890-0065, Japan.
Plant Cell Rep. 2014 Mar;33(3):499-510. doi: 10.1007/s00299-013-1550-y. Epub 2013 Dec 29.
A closer association of HSP90s with brassinosteroid signaling is suggested by the brassinosteroid-triggered formation of an HSP90-containing macromolecular complex and the direct interaction between HSP90.3 and BES1.
Heat shock protein 90 (HSP90) is a highly conserved molecular chaperone that is reportedly involved in the proper folding, stabilization, intracellular trafficking, maintenance and degradation of numerous proteins, as well as the facilitation of cellular signaling in various organisms including plants. Brassinosteroids (BRs), a class of unique steroidal hormones, play crucial roles in plant growth and development. The interaction between HSP90 proteins and BR action has been poorly understood. Here, we present molecular evidence suggesting that HSP90 proteins have a function(s) in BR signal transduction. First, blue native/sodium dodecyl sulfate-polyacrylamide gel electrophoresis linked immunoblotting demonstrated that a bioactive BR, brassinolide (BL), promotes the formation of some HSP90-containing macromolecular complexes with molecular weight more than 480 kDa in Arabidopsis T87 cultured cells. Second, HSP90.3, one of seven Arabidopsis HSP90 family proteins, was observed to interact in vitro with BRI1-EMS-SUPPRESSOR 1 (BES1), a transcription factor acting in BR signaling. Geldanamycin, an inhibitor of ATPase activity in HSP90, not only diminished HSP90.3 interaction with BES1 in vitro, but also suppressed BL-induced down-regulation of two BR biosynthesis genes, CONSTITUTIVE PHOTHOMORPHOGENESIS AND DWARFISM and DWARF4 in vivo. The results suggest the involvement of the HSP90/BES1 heterocomplexes in BR signaling-mediated feedback control in BR contents. Together, our results provide important clues to elucidate HSP90s' functions in the BR signaling pathway in Arabidopsis.
油菜素内酯触发形成含HSP90的大分子复合物以及HSP90.3与BES1之间的直接相互作用，表明HSP90与油菜素内酯信号传导之间存在更紧密的关联。
热休克蛋白90（HSP90）是一种高度保守的分子伴侣，据报道它参与多种蛋白质的正确折叠、稳定、细胞内运输、维持和降解，以及促进包括植物在内的各种生物体中的细胞信号传导。油菜素内酯（BRs）是一类独特的甾体激素，在植物生长发育中起关键作用。HSP90蛋白与BR作用之间的相互作用尚不清楚。在这里，我们提供了分子证据，表明HSP90蛋白在BR信号转导中具有功能。首先，蓝色非变性/十二烷基硫酸钠-聚丙烯酰胺凝胶电泳联用免疫印迹表明，一种生物活性BR，油菜素内酯（BL），促进了拟南芥T87培养细胞中一些分子量超过480 kDa的含HSP90的大分子复合物的形成。其次，观察到拟南芥HSP90家族的七个蛋白之一HSP90.3在体外与BR信号传导中的转录因子BRI1-EMS-抑制因子1（BES1）相互作用。格尔德霉素是HSP90中ATP酶活性的抑制剂，它不仅在体外减少了HSP90.3与BES1的相互作用，而且在体内抑制了BL诱导的两个BR生物合成基因CONSTITUTIVE PHOTHOMORPHOGENESIS AND DWARFISM和DWARF4的下调。结果表明HSP90/BES1异源复合物参与了BR信号传导介导的BR含量反馈控制。总之，我们的结果为阐明HSP90在拟南芥BR信号通路中的功能提供了重要线索。
