Genetic Improvement and Molecular Mechanisms of Waterlogging Tolerance in Soybean

Continuous climate changes are making flood-caused waterlogging stress more severe with a predicted 30% increase in heavy precipitations by 2030. Waterlogging is also confounded by an increased application of irrigation that could result in excess water. In our group, soybean is used as a model crop to address the urgent demands of improving waterlogging tolerance and understanding the underlying molecular mechanisms in plants. Screening of a core set of USDA germplasm including the wild species identified several waterlogging tolerant lines, which were used to develop mapping populations. Four quantitative trait loci (QTL) were mapped from two mapping populations and the favorable alleles of two major QTL are from exotic parents. Fine-mapping of a major QTL delimited the QTL into a genomic region containing one gene. The tolerant allele was found to have an insertion of 11-bp poly-A in the 5'-untranslated-region, which suppresses its own translation and promotes root growth under both non-stress and stress conditions. The naturally-occurring variations between the two alleles in root growth and waterlogging tolerance were confirmed by studies in soybean transgenic roots and composite transgenic plants. Phylogenetic analysis revealed that the tolerant allele is a recently raised mutation and has not been introduced into current US elite germplasms. By comparing field performance of the near-isogenic-lines, the tolerant allele was observed to improve yield by 16-40% under non-stress conditions possibly due the better root system. These findings not only provided genetic/genomic resources to protect yield during current climate changes in soybean, but also revealed the potential benefit of modification of the same type genes and the importance of root growth in crop improvement of yield and yield under abiotic stresses.