Natural variation in BjuB05.IRT1 is associated with cadmium accumulation in Brassica juncea

Phytoremediation of cadmium (Cd)-contaminated agricultural soils requires suitable germplasm and an improved understanding of the genetic factors underlying Cd accumulation. Here, we evaluated a genetically diverse panel of 165 Brassica juncea accessions and identified BJ20 as a high-Cd-accumulating genotype. Across two years, two sites, and two developmental stages, BJ20 consistently accumulated more Cd than the low-accumulating genotype BJ25. Mean shoot Cd accumulation reached 111.21 μg plant⁻¹ in BJ20, compared with 55.07 μg plant⁻¹ in BJ25. However, BJ20 had a lower root-to-shoot translocation factor than BJ25 (1.68 versus 2.30). Thus, its greater shoot Cd accumulation was not accompanied by greater proportional root-to-shoot transfer. Population resequencing and structure-adjusted association analysis identified an A/G SNP at the fourth coding nucleotide of BjuB05.IRT1, resulting in a Thr-to-Ala substitution at residue 2. The haplotype association with shoot Cd concentration was significant at flowering (P = 0.048), but not at maturity (P = 0.155). Differences in transcript abundance at flowering did not explain the contrasting phenotypes. In heterologous yeast assays, the BJ20-type allele increased Cd accumulation in the Cd-sensitive Δycf1 mutant to 455.76 ± 47.09 μg g⁻¹ , approximately 9.5-fold that of yeast expressing the BJ25-type allele. Together, the field, population-association, expression, and yeast results support BjuB05.IRT1 as a candidate contributing to natural variation in Cd accumulation-related traits. BJ20 therefore warrants site-specific evaluation as a phytoextraction resource. Low-accumulating germplasm may provide candidates for low-Cd breeding, subject to direct measurement of Cd concentrations in edible tissues.