Pearl millet WRKY transcription factor PgWRKY52 positively regulates salt stress tolerance through ABA-MeJA mediated transcriptional regulation
Jeky Chanwala, Khushbu Kumari, Deepak Kumar Jha, Mrunmay Kumar Giri, Nrisingha Dey
Abstract
• The PgWRKY52 is localized in the nucleus and has self-transactivation ability, confirming its role as a transcription factor. • Overexpression of PgWRKY52 improves salt stress tolerance by modulating ROS levels and enhancing physiological responses in transgenic plants. • The PgWRKY52 promoter enriched with conserved CREs and is strongly inducible under abiotic stress conditions. Environmental stresses adversely affect plant growth and development by disturbing physiological and metabolic equilibrium. Plants counteract these stresses through intricate genetic and biochemical pathways, which are largely mediated by signalling networks that involve key transcription factors (TFs). Among these, WRKY TFs are crucial in modulating plant responses to various stresses. In previous studies, WRKY TFs have been identified in millets. However, their functional characterization in millets remains vastly unexplored. Therefore, we have isolated and characterized PgWRKY52 , a Group IIc WRKY TFs from pearl millet, along with its upstream promoter region to understand its functional regulatory role. Ectopic expression of PgWRKY52 in transgenic Arabidopsis improved seed germination under salt stress and phytohormonal treatments of abscisic acid (ABA) and methyl jasmonate (MeJA). Improved stress tolerance was linked to reduced reactive oxygen species (ROS) accumulation and upregulation of stress-responsive genes, indicating an enhanced defense system. Promoter analysis unveiled that the PgWRKY52 promoter was constitutively active across vegetative and reproductive tissues, with strong stress-inducible activity under salt, heat, and ABA treatments. Cis-regulatory element (CRE) analysis identified key stress-responsive elements, including ABRE, MYB, W-box and MYC, which were validated through mutational studies as essential for promoter activity. Additionally, PgWRKY52 exhibited W-box-dependent DNA-binding capability, a characteristic feature of WRKY TFs. These findings emphasize the important function of the PgWRKY52 promoter in driving stress-responsive transcription. Altogether, these findings establish PgWRKY52 as a stress-responsive TF that enhances salt stress tolerance through crosstalk of ABA-MeJA signalling pathways and the regulatory role of its promoter, presenting a promising tool for developing climate-resilient crops.