Hansen Maureen, Chae Hyun Sook, Kieber Joseph J
Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA.
Plant J. 2009 Feb;57(4):606-14. doi: 10.1111/j.1365-313X.2008.03711.x. Epub 2008 Oct 10.
A major question in plant biology is how phytohormone pathways interact. Here, we explore the mechanism by which cytokinins and brassinosteroids affect ethylene biosynthesis. Ethylene biosynthesis is regulated in response to a wide variety of endogenous and exogenous signals, including the levels of other phytohormones. Cytokinins act by increasing the stability of a subset of ACC synthases, which catalyze the generally rate-limiting step in ethylene biosynthesis. The induction of ethylene by cytokinin requires the canonical cytokinin two-component response pathway, including histidine kinases, histidine phosphotransfer proteins and response regulators. The cytokinin-induced myc-ACS5 stabilization occurs rapidly (<60 min), consistent with a primary output of this two-component signaling pathway. We examined the mechanism by which another phytohormone, brassinosteroid, elevates ethylene biosynthesis in etiolated seedlings. Similar to cytokinin, brassinosteroid acts post-transcriptionally by increasing the stability of ACS5 protein, and its effects on ACS5 were additive with those of cytokinin. These data suggest that ACS is regulated by phytohormones through regulatory inputs that probably act together to continuously adjust ethylene biosynthesis in various tissues and in response to various environmental conditions.
植物生物学中的一个主要问题是植物激素途径如何相互作用。在这里，我们探究细胞分裂素和油菜素甾醇影响乙烯生物合成的机制。乙烯生物合成受多种内源性和外源性信号调控，包括其他植物激素的水平。细胞分裂素通过增加一部分1-氨基环丙烷-1-羧酸（ACC）合成酶的稳定性来发挥作用，这些酶催化乙烯生物合成中通常的限速步骤。细胞分裂素诱导乙烯生成需要经典的细胞分裂素双组分响应途径，包括组氨酸激酶、组氨酸磷酸转移蛋白和响应调节因子。细胞分裂素诱导的myc-ACS5稳定化迅速发生（<60分钟），这与该双组分信号通路的主要输出一致。我们研究了另一种植物激素油菜素甾醇提高黄化幼苗中乙烯生物合成的机制。与细胞分裂素类似，油菜素甾醇通过增加ACS5蛋白的稳定性在转录后发挥作用，并且其对ACS5的影响与细胞分裂素的影响具有加和性。这些数据表明，ACS受植物激素通过调控输入进行调节，这些调控输入可能共同作用，以在各种组织中并响应各种环境条件持续调节乙烯生物合成。
