Genome-wide characterization of the Hsf gene family and its transcriptional responses to drought stress in loquat (Eriobotrya japonica)

Loquat ( Eriobotrya japonica ) is an economically important subtropical fruit tree characterized by its unique evergreen habit and winter flowering. This distinct phenology renders it highly susceptible to seasonal drought. Such drought conditions can severely reduce fruit yield and quality. Heat shock transcription factors (HSFs) are pivotal regulators of stress adaptation. However, their specific roles and regulatory mechanisms in the drought response of loquat remain largely unexplored. In this study, a total of 21 EjHsf genes were identified in the loquat genome and categorized into three evolutionarily conserved classes (A, B, and C). Promoter analysis identified multiple putative hormone- and stress-responsive motifs, including abscisic acid-responsive elements (ABREs) and methyl jasmonate-responsive motifs. Furthermore, homology-based STRING analysis predicted functional associations between the Arabidopsis homologues corresponding to EjHsf proteins and several Hsps, suggesting that EjHsf proteins may participate in stress-related functional networks. Physiological assays revealed drought-intensity- and duration-dependent changes in superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities and malondialdehyde (MDA) content. Gene expression analysis further showed that the expression patterns of specific EjHsf members were temporally associated with these physiological responses. The examined EjHsf genes displayed distinct time- and drought-intensity-dependent expression patterns. Notably, EjHsfB2a was consistently induced under moderate drought at both time points, whereas other genes showed transient or treatment-dependent responses. This study represents the first systematic characterization of the EjHsf family in loquat under drought stress. By elucidating the evolutionary context and transcriptional responses of these genes, this study identifies EjHsfB2a as a promising candidate for future functional characterization, thereby laying a theoretical foundation for the genetic improvement of drought tolerance in evergreen fruit trees.