Insights into the SULTR gene family of Solanum americanum: Genome-wide identification, expression profiling, and functional response to cadmium stress

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The SULTR gene family encodes sulfate transporters that play a critical role in sulfur uptake and redistribution in plants and are closely associated with responses to abiotic stress. However, their functions in the Cd hyperaccumulator Solanum americanum remain unclear. In this study, a genome-wide analysis identified 14 SaSULTR members from the S. americanum genome and classified them into four subfamilies based on conserved domain architecture and phylogenetic relationships. Their evolutionary characteristics in terms of gene structure, conserved motifs, chromosomal distribution, and collinearity were analyzed. Promoter analysis revealed multiple hormone-responsive cis-elements, including those responsive to ABA and MeJA, suggesting a potential role in stress regulation. Protein sequence alignment and molecular docking consistently showed that all SaSULTR proteins possess highly conserved sulfate-binding sites. Expression profiling revealed that SaSULTR1;2 and SaSULTR4 were significantly upregulated in roots under both Cd stress and sulfur starvation, and their expression levels were positively correlated with that of the key sulfur assimilation enzyme ATP sulfurylase (ATPS). Functional complementation assays further demonstrated that SaSULTR1;2 and SaSULTR4 could restore the growth of SULTR-deficient yeast mutants under Cd stress, confirming their sulfate transport capacity and involvement in Cd detoxification. This study provides the first systematic analysis of the SULTR gene family in a Cd hyperaccumulator, identifying SaSULTR1;2 and SaSULTR4 as key players in sulfate transport and Cd detoxification, and providing promising genetic targets for the phytoremediation of Cd-contaminated soils.

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