A role for phospholipase A in auxin‐regulated gene expression

Abstract

Auxin increases phospholipase A(2) activity within 2min (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 A(2) 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 PLA(2) inhibitors using seedlings expressing beta-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.

Function and regulation of phospholipid signalling in plants

“…Arabidopsis 5PTase13 and PLD ζ 2 regulate the cotyledon vein [40] and root development [20] respectively by modulating auxin synthesis and transport. PLA activity is rapidly induced by auxin within 2 min [47], and Arabidopsis sPLA2 regulates shoot gravitropism by regulating auxin-induced cell elongation [48]. …”

Phospholipase A2 Is Required for PIN-FORMED Protein Trafficking to the Plasma Membrane in theArabidopsisRoot

“…PLA 2 hydrolysis products act as signaling molecules for diverse cellular processes in plants (for reviews, see Scherer, 2002;Ryu, 2004). In particular, PLA 2 has been reported to function in auxinmediated phenomena such as gravitropism and cell elongation (Yi et al, 1996;Scherer, 2002;Lee et al, 2003;Ryu, 2004;Scherer et al, 2007). It remains to be determined whether ONOinhibitable PLA 2 s regulate vesicle trafficking by affecting signal transduction, which involves their hydrolytic products, or by another mechanism.…”

Plant phospholipid signaling: “in a nutshell”

“…As such, it is not always clear whether effects reflect general lipid metabolism or signaling. Nonetheless, evidence is increasing for PLAʼs involvement in disease resistance, auxin, and light (Table 1; [35][36][37][38][39].…”