Transcriptome analysis of HMG family in Salix × Jiangsunesis ‘J795’: characterization, expression patterns and roles in sex differentiation

The molecular mechanisms underlying sex differentiation in willows remain elusive. To uncover these mechanisms, we performed RNA-Seq on ‘J795’ male, female, and bisexual inflorescences collected from a unique mutant willow that is monoecious but also produces female individuals. The results revealed 7,089 DEGs between female and male flowers, 3,220 DEGs between bisexual and male flowers, and 3,688 DEGs between bisexual and female flowers in ‘J795’. Gene Ontology (GO) enrichment analysis indicated that the DEGs between female and male flowers, as well as between bisexual and male flowers, were primarily associated with microtubule-based movement and activity. In contrast, DEGs between bisexual and female flowers were mainly enriched in microtubule activity and pollen tube regulation. HMGMost members of the HMG were highly expressed in bisexual flowers, while several pivotal members exhibited markedly elevated expression in male flowers, implying their potential regulatory roles in male flower development of ‘J795’. Genome-wide analysis identified 19 HMG genes in the willow genome, distributed across 12 chromosomes, including six tandem duplicate pairs. qRT-PCR classified the expression patterns of these 19 HMG genes into three categories: highest in male flowers, highest in female flowers, and relatively high in both female and bisexual flowers. Notably, HMG18 exhibited the highest expression level in male flowers, suggesting a potential crucial role in the development of male flowers in Salix. In summary, this study represents the first transcriptomic investigation into sex-related genes using a unique mutant willow germplasm. Our findings provide valuable genetic resources for understanding sex differentiation, stamen and pistil development, and sex determination in willow.