BcWRKY25-BcWRKY33A-BcLRP1/BcCOW1 module promotes root development for improved salt tolerance in Bok choy

Abstract Root development is a complex process involving phytohormones and transcription factors. Our previous research has demonstrated that BcWRKY33A is significantly expressed in Bok choy roots under salt stress, and heterologous expression of BcWRKY33A increases salt tolerance and promotes root development in transgenic Arabidopsis. However, the precise molecular mechanisms by which BcWRKY33A governs root development remain elusive. Here, we investigated the role of BcWRKY33A in both root elongation and root hair formation in transgenic Bok choy roots. Our data indicated that overexpression of BcWRKY33A stimulated root growth and stabilized root hair morphology, while silencing BcWRKY33A prevented primary root elongation and resulted in abnormal root hairs morphology. Meanwhile, our research uncovered that BcWRKY33A directly binds to the promoters of BcLRP1 and BcCOW1, leading to an upregulation of their expression. In transgenic Bok choy roots, increased BcLRP1 and BcCOW1 transcript levels improved primary root elongation and root hair formation, respectively. Additionally, we pinpointed BcWRKY25 as a NaCl-responsive gene that directly stimulates the expression of BcWRKY33A in response to salt stress. All results shed light on the regulatory mechanisms governing root development by BcWRKY25-BcWRKY33A-BcLRP1/BcCOW1 module and propose potential strategies for improving salt tolerance in Bok choy.