GmWRKY81 Encoding a WRKY Transcription Factor Enhances Aluminum Tolerance in Soybean

Abstract

Aluminum (Al) toxicity is an essential factor that adversely limits soybean (<i>Glycine max</i> (L.) Merr.) growth in acid soils. WRKY transcription factors play important roles in soybean responses to abiotic stresses. Here, <i>GmWRKY81</i> was screened from genes that were differentially expressed under Al treatment in Al-tolerant soybean Baxi10 and Al-sensitive soybean Bendi2. We found that <i>GmWRKY81</i> was significantly induced by 20 μM AlCl₃ and upregulated by AlCl₃ treatment for 2 h. In different tissues, the expression of <i>GmWRKY81</i> was differentially induced. In 0-1 cm root tips, the expression of <i>GmWRKY81</i> was induced to the highest level. The overexpression of <i>GmWRKY81</i> in soybean resulted in higher relative root elongation, root weight, depth, root length, volume, number of root tips and peroxidase activity but lower root average diameter, malonaldehyde and H₂O₂ contents, indicating enhanced Al tolerance. Moreover, RNA-seq identified 205 upregulated and 108 downregulated genes in <i>GmWRKY81</i> transgenic lines. Fifteen of these genes that were differentially expressed in both AlCl₃-treated and <i>GmWRKY81</i>-overexpressing soybean had the W-box element, which can bind to the upstream-conserved WRKY domain. Overall, the combined functional analysis indicates that <i>GmWRKY81</i> may improve soybean Al tolerance by regulating downstream genes participating in Al³⁺ transport, organic acid secretion and antioxidant reactions.