Interspecies Conservation of Gene Expression Patterns in Brassica Reproductive Organs Unveiled by Comparative Transcriptomics

Brassica species evolved through recurrent polyploidization and chromosomal rearrangements, forming diploid progenitors that hybridize into allopolyploids. These plants exhibit remarkable morphological diversity, with specialized edible organs including leaf-, stem-, root-, and oil-type cultivars, yet cross-species multi-organ transcriptomic studies elucidating their gene expression similarities and divergences remain lacking. To address this gap, we analyzed publicly available transcriptomes (downloaded from NCBI SRA) from eight organs (embryo, seed coat, silique, root, stem, leaf, flower and seedling) across six U’s Triangle species (Brassica rapa, B. nigra, B. oleracea, B. juncea, B. napus, B. carinata), revealing that (1) reproductive organs show higher gene expression conservation (GEC), particularly embryos (p < 0.05); (2) lineage-specific subgenome dominance patterns (BnaC/BjuB/BcaC) persist across organs; and (3) ancestral subgenomes functionally specialize, with MF2-subgenome transcription factors (YABBY/GRF) regulating embryogenesis and LF/MF1-subgenome MYBs controlling seed coat development. Comparative analyses demonstrate floral GEC exceeds that of the Arabidopsis thaliana homologs, while also exhibiting seed-specific divergence patterns. This study establishes a comprehensive Brassica multispecies expression atlas, elucidating organ-specific evolutionary conservation principles and providing molecular insights into subgenome functional partitioning, which offers valuable perspectives for understanding Brassica evolutionary mechanisms and crop improvement strategies.