The Arabidopsis Cysteine-Rich GASA5 Is a Redox-Active Metalloprotein that Suppresses Gibberellin Responses

Dear Editor, The plant-specific GIBBERELLIN (GA)-STIMULATED TRANSCRIPT 1 (GAST1)-like genes have been identified in numerous plant species and many of them are regulated by the phytohormone GA.All encode small proteins with a conserved cysteine-rich C-terminus,containing 12 cysteines in conserved positions.The fact that the number and positions of all 12 cysteines have not changed during the course of evolution strongly implies fundamental and important biochemical and biological functions.Although many of these genes were characterized,and different biological functions were suggested,almost nothing is known about their mode of action.We previously showed that the petunia GAST1-like GA INDUCED 2 (GIP2) and its Arabidopsis homolog GA STIMULATED 4 (GASA4) promote typical GA responses and have redox activity (Wigoda et al.,2006;Rubinovich and Weiss,2010).Mutated GASA4,in which four conserved cysteines were replaced by alanines,lost its redox activity and the ability to promote GA responses,suggesting that the two functions are linked (Rubinovich and Weiss,2010).