Overexpression of BnaMATE43b Improves Resistance to Aluminum Toxicity and Identification of Its Upstream Transcription Factors in Rapeseed (Brassica napus L.)

The multidrug and toxic compound extrusion (MATE) protein plays a crucial role in mediating plant responses to aluminum (Al) toxicity. The key candidate gene <i>BnaMATE43b</i> related to Al toxicity stress in rapeseed was identified using GWAS and transcriptome analysis. In this study, the <i>BnaMATE43b</i> gene was cloned and functionally characterized in rapeseed. Compared with wild-type rapeseed (WT), the <i>BnaMATE43b</i> overexpression lines (OE) demonstrated stronger aluminum tolerance, specifically manifested in higher relative elongation of taproots (RETs) and relative total root length (RTRL); under Al toxicity stress, the enzyme activities (SOD and POD) and root activity were significantly increased in the OE lines, whereas the MDA content and relative electrical conductivity were reduced in rapeseed root. Further transcriptome analysis of OE-3 showed that the differentially expressed genes (DEGs) were mainly enriched in zeatin biosynthesis (map00908), glucosinolate biosynthesis (map00966), phenylpropanoid biosynthesis (map00940), and ascorbate and aldarate metabolism (map00053). In addition, the yeast cDNA library of rapeseed was constructed, and twenty-two candidate upstream transcription factors (UTFs) of <i>BnaMATE43b</i> were screened; furthermore, four candidate UTFs were obtained through one-on-one interaction validation and luciferase assays, comprising three bHLH transcription factors (<i>BnaA02g28220D</i>, <i>BnaA06g07840D</i>, and <i>BnaA08g24520D</i>) and one ERF transcription factor (<i>BnaA05g23130D</i>). Collectively, these results suggest that <i>BnaMATE43b</i> could improve Al tolerance in rapeseed by mediating antioxidant enzyme activities and the related metabolic pathway, while the obtained UTFs lay the foundation for further analysis of the gene regulatory network under Al toxicity stress.