Molecular mechanism analysis of LdHSFB2a in lily thermotolerance.

Heat stress (HS) is a major environmental stress that inhibits plant growth and development. Plants have evolved various mechanisms to cope with heat stress, a key one being the HSF-HSP (Heat stress transcription factor-Heat shock protein) signaling pathway. HSFs can be divided into three classes: A, B, and C. In this study, we report the identification and functional characterization of a specific B2 member LdHSFB2a in Lilium davidii var. unicolor. RT-qPCR (Real-time Quantitative Polymerase Chain Reaction) analyses indicated that LdHSFB2a was highly expressed in HS-exposed leaves. LdHSFB2a was localized in the nucleus, consistent with the characterization of transcription factors. In contrast to other HSFBs, LdHSFB2a did not contain the typical B3 repression domain but exhibited transcriptional repression activity in yeast and plant cells. Transient overexpression and virus-induced gene silencing (VIGS) of LdHSFB2a in lily petals suggested that LdHSFB2a functions positively in lily thermotolerance. Consistent with the implication of LdHSFB2a function in thermotolerance, further analysis revealed that the expression levels of HSFA1, HSFA2, and MBF1c were increased as LdHSFB2a was overexpressed but reduced as LdHSFB2a was silenced. Furthermore, LdHSFB2a bound to the promoters of HSFA3 A, WRKY33, CAT2, and GLOS1. And LdHSFB2a overexpression and silencing enhanced and reduced their expressions, respectively. Therefore, we speculated that LdHSFB2a may be a coactivator that interacts with transcriptional activators to promote thermotolerance in lily by enhancing the expression of heat-responsive genes such as HSFA3 A, WRKY33, CAT2, and GLOS1.