Genome-wide analysis of the HSF gene family in lily and functional characterization of LdHSFC1 under heat stress.

Genome-wide analyses reveal extensive HSF expansion in lily, and functional assays identify LdHSFC1 as a heat-induced transcriptional repressor that reduces thermotolerance by directly suppressing LdHSFA2. Heat shock transcription factors (HSFs) are key regulators of plant thermotolerance, but their genome-wide characteristics and functions in lily are poorly characterized. We identified 48, 62, and 114 HSF genes in Lilium davidii var. unicolor, L. sargentiae, and L. regale, respectively. Comparative analyses of phylogeny, gene structure, conserved motifs, chromosomal distribution, and synteny revealed that lily HSF genes retain conserved core domains, but have undergone considerable expansion and diversification, particularly within class B and class C. Promoter analysis and transcriptome profiling suggested that numerous HSF genes are heat-responsive and potentially integrate stress, hormonal, and developmental signals. LdHSFC1 was notably induced by heat treatment. This protein localized to the nucleus and functioned as a transcriptional repressor. Transient transformation assays confirmed that LdHSFC1 damages lily thermotolerance. Furthermore, overexpression of LdHSFC1 suppressed, whereas its silencing enhanced the expression of LdHSFA1, LdHSFA2, LdHSFA3 and LdMBF1c. Yeast one-hybrid and dual-luciferase assays further showed that LdHSFC1 binds directly to the LdHSFA2 promoter to repress its transcription. Collectively, this work presents the first genome-wide overview of the lily HSF family and identifies LdHSFC1 as a negative regulator of thermotolerance. These findings broaden the understanding of heat-responsive transcriptional regulation in ornamental plants and highlight potential targets for enhancing lily thermotolerance.