Characterization and Functional Analysis of FaHsfC1b from Festuca arundinacea Conferring Heat Tolerance in Arabidopsis.

Heat transcription factors ( Hsfs ) belong to a large gene family classified into A, B, and C groups, with classes A and B Hsfs being well-characterized and known for their roles in plant tolerance to abiotic stresses. The functions and roles of Class C Hsfs are not well-documented. The objectives of this study were to characterize a class C Hsf gene ( FaHsfC1b ) cloned from tall fescue ( Festuca arundinacea ), a perennial grass species, and to determine the physiological functions of FaHsfC1b in regulating heat tolerance by overexpressing FaHsfC1b in Arabidopsis thaliana . Full length cDNA of FaHsfC1b was cloned and the sequence alignment showed that it had high similarity to OsHsfC1b with typical DNA binding domain, hydrophobic oligomerization domain, and a nucleus localization signal. Transient expression with FaHsfC1b -eGFP in protoplasts of Arabidopsis leaves indicated its nucleus localization. qRT-PCR analysis showed that FaHsfC1b responded to heat, osmotic, salt, and cold stress in leaves and roots during 48-h treatment. Physiological analysis showed that FaHsfC1b overexpression enhanced plant survival rate, chlorophyll content, and photochemical efficiency, while it resulted in decreases in electrolyte leakage, H₂O₂ and O2- content under heat stress. qRT-PCR showed that endogenous HsfC1 was induced in transgenic plants and the expression levels of heat protection protein genes, including several HSPs , AtGalSyn1 , AtRof1 , and AtHSA32 , as well as ABA-synthesizing gene ( NCED3 ) were significantly upregulated in transgenic plants overexpressing FaHsfC1b under heat stress. Our results first demonstrate that HsfC1b plays positive roles in plant tolerance to heat stress in association with the induction and upregulation of heat-protective genes. HsfC1b may be used as a candidate gene for genetic modification of cool-season plant species for improving heat tolerance.