Wheat transcription factor TaWRKY51 promotes lateral root formation through negatively regulating ethylene biosynthesis in Arabidopsis
Rui Wang, Fei Meng, Hualing Wu, Yingyin Yao, Zhongfu Ni, Qixin Sun

China Agricultural University, Beijing, 100094, PR China

Abstract
Transcription factor WRKY participated in plant response to stress, as well as plant development. Negative role of WRKY proteins in lateral root development was reported in Arabidopsis and rice, however, the positive role and underlying regulatory mechanism of WRKY protein in lateral root formation were poorly understood. In this study, we identified a wheat WRKY transcription factor, TaWRKY51, which belongs to group II member, is expressed in root, up-regulated during the leaf senescence, and localized in the nucleus. Overexpression of TaWRKY51 significantly promoted lateral root formation in Arabidopsis. Several lines of evidences indicated that positive regulation of lateral root formation by TaWRKY51 is mediated by ethylene biosynthesis and ethylene signal pathway. Firstly, overexpression of TaWRKY51 (designated 35S::TaWRKY51) significantly reduced ethylene production through directly binding to the W-box present in the promoter of ethylene biosynthesis gene AtACS2 and downregulating its expression. Secondly, overexpression of AtACS2 in 35S::TaWRKY51 lines significantly reduced the lateral root numbers, and overexpression of TaWRKY51 in the mutant eto1-1 rescued the lateral root morphology. Thirdly, application of exogenous ACC and ethephone reduced lateral root number in 35S::TaWRKY51 lines. Fourthly, genetic approaches were used to test whether the increased lateral root formation is dependent on ethylene signal pathway, and it was shown that overexpression of TaWRKY51 in ctr1-1 mutant could not rescue the lateral root phenotype of ctr1-1. Auxin transporter AUX1 gene is down-regulated in 35S::TaWRKY51 lines, which could redirect auxin distribution, and overexpression of TaWRKY51 in Arabidopsis arf7/arf19 double mutant could not rescue the lateral root phenotype of the mutant. These data demonstrated that TaWRKY51-regulated lateral root formation is also dependent on the auxin signal. A model for the TaWRKY51 to promote lateral root formation through reducing ethylene production, mediated by auxin response pathway, was proposed.