Genome-Wide Characterization and Heat Responsive Expression Profiling of the HSP10 Co-Chaperonin Gene Family in Brassica juncea

Heat stress disrupts protein homeostasis, yet the thermoregulatory roles of HSP10/CPN10 co-chaperonins in polyploid crops remain unexplored. This study conducted the first genome-wide characterization of the HSP10 gene family in allotetraploid Brassica juncea to identify heat tolerance candidates. Genome-wide identification of BjuHSP10 genes was performed across A and B subgenomes, followed by phylogenetic, gene structure, duplication, synteny, promoter, and structural analyses. Transcriptional responses were evaluated under moderate (28/24 °C) and severe (36/32 °C) heat stress conditions. Ten BjuHSP10 genes were identified, encoding six mitochondrial, three chloroplast-targeted, and one cytoplasmic protein. Mitochondrial members were small (~10.7 kDa) with three-exon structures, whereas chloroplast members were larger (15.5–27.1 kDa) with complex exon–intron organization. Segmental duplication drove family expansion (19 duplicated pairs), with differential retention of Arabidopsis homologs. Promoter regions contained 391 putative cis-regulatory elements associated with stress, hormonal, and developmental regulation. Under heat stress, BjuHSP10-4 and BjuHSP10-5 were induced under both treatments; BjuHSP10-1/3/6/9 responded only to severe stress, while four genes were repressed. Structural modeling confirmed conserved β-rich GroES/CPN10-like folds. These findings identify candidate BjuHSP10 genes, particularly BjuHSP10-4 and BjuHSP10-5, as promising targets for heat-tolerance improvement in mustard, providing a foundation for future breeding and functional studies in polyploid crops.