A Novel GmSIN1-GmRNF1a-GmCSN5a Module Determines Soybean Salt Tolerance and Yield Under Saline Soil Conditions.

Soybean (Glycine max) is a major source of dietary protein and vegetable oil, but its production is severely reduced by salt stress. The regulatory mechanisms and utilization of salt-tolerant genes have not been deeply studied. Salt-Induced NAC 1 (GmSIN1) positively regulates salt tolerance in soybean, enhancing growth and yield in saline soil. Here, we found that GmSIN1 is degraded via the 26S proteasome pathway, and this process is suppressed by salt. GmRNF1a mediates the ubiquitination-dependent degradation of GmSIN1 as an E3 ubiquitin ligase, whereas GmCSN5a (a homolog of COP9 signalosome subunit) directly inhibits its E3 ligase activity. GmRNF1a negatively regulates salt tolerance while GmCSN5a functions as a positive regulator. We further identified elite haplotypes of GmSIN1, GmRNF1a, and GmCSN5a that associate with grain weight per plant under both normal and saline conditions. Gene-pyramided lines carrying elite alleles (GmSIN1(Hap1)-GmRNF1a(Hap2)-GmCSN5a(Hap1)) exhibit boosted grain yield under both conditions. In conclusion, our study reveals that the GmSIN1-GmRNF1a-GmCSN5a module enhances soybean salt tolerance by maintaining GmSIN1 orthostasis. Pyramiding elite haplotypes establishes an innovative haplotype-based breeding strategy for developing salt-tolerant and high-yielding soybean cultivars by harnessing natural variation.