GmSALT3, Which Confers Improved Soybean Salt Tolerance in the Field, Increases Leaf Cl- Exclusion Prior to Na+ Exclusion But Does Not Improve Early Vigor under Salinity

Abstract

Soil salinity reduces soybean growth and yield. The recently identified <i>GmSALT3</i> (<i>Glycine max</i> salt Tolerance-associated gene on chromosome 3) has the potential to improve soybean yields in salinized conditions. Here we evaluate the impact of <i>GmSALT3</i> on soybean performance under saline or non-saline conditions. Three sets of near isogenic lines (NILs), with genetic similarity of 95.6-99.3% between each pair of NIL-T and NIL-S, were generated from a cross between two varieties 85-140 (salt-sensitive, S) and Tiefeng 8 (salt-tolerant, T) by using marker-assisted selection. Each NIL-T; 782-T, 820-T and 860-T, contained a common ~1000 kb fragment on chromosome 3 where <i>GmSALT3</i> was located. We show that <i>GmSALT3</i> does not contribute to an improvement in seedling emergence rate or early vigor under salt stress. However, when 12-day-old seedlings were exposed to NaCl stress, the NIL-T lines accumulated significantly less leaf Na⁺ compared with their corresponding NIL-S, while no significant difference of K⁺ concentration was observed between NIL-T and NIL-S; the magnitude of Na⁺ accumulation within each NIL-T set was influenced by the different genetic backgrounds. In addition, NIL-T lines accumulated less Cl^- in the leaf and more in the root prior to any difference in Na⁺; in the field they accumulated less pod wall Cl^- than the corresponding NIL-S lines. Under non-saline field conditions, no significant differences were observed for yield related traits within each pair of NIL-T and NIL-S lines, indicating there was no yield penalty for having the <i>GmSALT3</i> gene. In contrast, under saline field conditions the NIL-T lines had significantly greater plant seed weight and 100-seed weight than the corresponding NIL-S lines, meaning <i>GmSALT3</i> conferred a yield advantage to soybean plants in salinized fields. Our results indicated that <i>GmSALT3</i> mediated regulation of both Na⁺ and Cl^- accumulation in soybean, and contributes to improved soybean yield through maintaining a higher seed weight under saline stress.