Walnut JrGSTU23 and JrVHAc4 involve in drought tolerance via JrWRKY2-mediated upstream regulatory pathway

Drought stress negatively affects the walnut productivity. To ensure the comprehensive benefits of walnut, this study aims to explore the molecular mechanism of drought stress response. Therefore, the downstream target genes of JrWRKY2, a drought tolerance regulator of Juglans regia, are identified by analyses of promoter expression, yeast one-hybrid and co-expression. The results showed that JrWRKY2 could bind to the W-BOX like motifs from the promoters of JrGSTU23 (a tau class glutathione S-transferase) and JrVHAc4 (a c subunit of vacuole H+-ATPase). JrGSTU23 and JrVHAc4 could be up-regulated by drought stress and abscisic acid (ABA). The drought tolerance of transgenic Arabidopsis overexpression of JrGSTU23 or JrVHAc4 were promoted significantly compared to wild type (WT) plants; More importantly, the degree of improvement in drought resistance is enhanced by application of ABA. The transcription levels of the genes from signaling pathways of ABA and mitogen-activated protein kinases (MAPKs) in JrGSTU23 and JrVHAc4 overexpression plants were higher than those in WT with different profiles. These results propose a trifurcate feed-forward pathway involving in JrWRKY2, JrGSTU23, and JrVHAc4 functions on drought stress response that associated with ABA and MAPK signaling pathways, which will offer new insights to reveal plant adaptation mechanism to adverse stimulus.