背景回顾：The phytohormone auxin is the major coordinative signal in plant development, mediating transcriptional reprogramming by a well-established canonical signalling pathway. TRANSPORT INHIBITOR RESPONSE 1 (TIR1)/AUXIN-SIGNALING F-BOX (AFB) auxin receptors are F-box subunits of ubiquitin ligase complexes. In response to auxin, they associate with Aux/IAA transcriptional repressors and target them for degradation via ubiquitination. 

主要发现：Here we identify adenylate cyclase (AC) activity as an additional function of TIR1/AFB receptors across land plants. 

结果1-cAMP的诱导产生：Auxin, together with Aux/IAAs, stimulates cAMP production. 

结果2-TIR1蛋白AC活性的功能：Three separate mutations in the AC motif of the TIR1 C-terminal region, all of which abolish the AC activity, each render TIR1 ineffective in mediating gravitropism and sustained auxin-induced root growth inhibition, and also affect auxin-induced transcriptional regulation. 

结论：These results highlight the importance of TIR1/AFB AC activity in canonical auxin signalling. They also identify a unique phytohormone receptor cassette combining F-box and AC motifs, and the role of cAMP as a second messenger in plants.

 摘 要 

植物激素生长素是植物发育的主要协调信号，通过一个已知的经典信号转导途径介导转录重编程。生长素受体蛋白TIR1/AFB是一类泛素连接酶复合体的F-box亚基。在响应于生长素时，这些受体蛋白能够靶向转录抑制子Aux/IAA蛋白，并介导后者经由泛素化途径的降解。本文中，作者发现陆地植物的TIR1/AFB受体还具有另外的功能，即存在腺苷酸环化酶（AC）活性。生长素与Aux/IAAs一起，能够刺激cAMP的产生。TIR1炭端区域AC基序的3个独立突变都会导致AC活性的丧失，这3种突变都会导致TIR1在向重力性以及生长素诱导的根生长抑制方面功能的缺失，同时还会影响生长素诱导的转录调控。这些研究结果表明TIR1/AFB受体腺苷酸环化酶活性在经典生长素信号转导中的重要作用。同时，本研究还鉴定了一个结合F-box和AC基序的特有植物激素受体盒，以及cAMP作为植物中第二信使的作用。

** Jiří Friml **