Genome-wide identification and expression analysis of the Hsf gene family in Rhododendron molle under heat stress

Rhododendron possesses significant ornamental and economic value; however, its limited heat tolerance severely hinders its broader development and application. Heat shock transcription factors (Hsfs) are extensively involved in various abiotic stress responses and play essential roles in plant thermotolerance and other physiological processes.

To identify Hsf genes in the genome of Rhododendron molle (R. molle) and investigate their regulatory mechanisms underlying heat tolerance in R. molle.

The Hsf gene family was systematically identified using the genomic data of R. molle, and the expression levels of RmHsf genes under heat stress were analyzed through Reverse Transcription Quantitative Polymerase Chain Reaction (RT-qPCR).

The RmHsf gene family consists of 25 members distributed across 12 chromosomes. Phylogenetic analysis demonstrated that the RmHsf genes are classified into three subfamilies: A, B and C. Most genes within the same subfamily share similar conserved motifs and gene structures. The cis-acting elements in the promoter regions of RmHsf genes are associated with plant hormone signaling and stress response pathways. Collinearity analysis revealed that the expansion of the RmHsf gene family primarily occurred through segmental and tandem duplication events. RT-qPCR results showed that RmHsfA2, RmHsfA3, RmHsfA7a, and RmHsfA7b were significantly upregulated under heat stress, suggesting that they may serve as key genes in the heat stress response of R. molle. Among them, RmHsfA2 and RmHsfA3 were notably induced by exogenous ethylene.

This study conducted a comprehensive genome-wide analysis of the Hsf gene family in R. molle, laying a solid foundation for functional validation of Hsf genes and the breeding of heat-tolerant cultivars.