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.