A role for phospholipase A in auxin-regulated gene expression

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• 作者：Gü ; nther F.E. Scherer ; Marc Zahn ; Judy Callis ; Alan M. Jones
• 关键词：Aux/IAA protein ; Auxin ; Degradation ; Phospholipase A ; TIR1
• 刊名：FEBS Letters
• 出版年：2007
• 出版时间：4 September 2007
• 年：2007
• 卷：581
• 期：22
• 页码：4205-4211
• 全文大小：1246 K

文摘

Auxin increases phospholipase A₂ activity within 2 min (Paul, R., Holk, A. and Scherer, G.F.E. (1998) Fatty acids and lysophospholipids as potential second messengers in auxin action. Rapid activation of phospholipase A₂ activity by auxin in suspension-cultured parsley and soybean cells. Plant J. 16, 601–611) and the phospholipase A inhibitors, ETYA and HELSS, inhibit elongation growth of etiolated Arabidopsis hypoctyls (Holk, A., Rietz, S., Zahn, M., Quader, H. and Scherer, G.F.E. (2002) Molecular identification of cytosolic, patatin-related phospholipases A from Arabidopsis with potential functions in plant signal transduction. Plant Physiol. 130, 90–101). To identify the mode of action, rapid auxin-regulated gene expression was tested for sensitivity to these PLA₂ inhibitors using seedlings expressing β-glucuronidase (GUS) under the control of the synthetic auxin-responsive promoter DR5. ETYA and HELSS inhibited the auxin-induced increases in GUS activity, the steady-state level of the corresponding GUS mRNA and the mRNAs encoded by four other auxin-induced genes, IAA1, IAA5, IAA19 and ARF19. Factors that bind to the auxin response elements of the DR5 promoter and thereby regulate gene expression are regulated by a set of proteins such as Aux/IAA1 whose abundances are, in part, under control of E3 ubiquitin ligase SCF complexes. To investigate this mechanism further, the effect of ETYA on Aux/IAA1 degradation rate was examined using seedlings expressing Aux/IAA1:luciferase fusion proteins. In the presence of cycloheximide and excluding synthesis of IAA1:luciferase, ETYA had no apparent effect on degradation rates of IAA1, either with or without exogenous auxin. Therefore, the E3 ubiquitin ligase SCF^TIR1 complex is an unlikely direct target of the PLA inhibitor. When cycloheximide was omitted, however, the inhibitors ETYA and HELSS blocked a sustained auxin-induced decrease in its steady-state level, indicating an unknown target capable to regulate Aux/IAA protein levels and, hence, transcription.