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

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