The class B heat shock factor HSFB1 regulates heat tolerance in grapevine.

Grape is a widely cultivated crop with high economic value. Most cultivars derived from mild or cooler climates may not withstand increasing heat stress. Therefore, dissecting the mechanisms of heat tolerance in grapes is of particular significance. Here, we performed comparative transcriptome analysis of 'Tangwei' (heat tolerant) and 'Jingxiu' (heat sensitive) grapevines after exposure to 25°C, 40°C, or 45°C for 2 h. More differentially expressed genes (DEGs) were detected in 'Tangwei' than in 'Jingxiu' in response to heat stress, and the number of DEGs increased with increasing treatment temperatures. We identified a class B Heat Shock Factor, HSFB1, which was significantly upregulated in 'Tangwei', but not in 'Jingxiu', at high temperature. VdHSFB1 from 'Tangwei' and VvHSFB1 from 'Jingxiu' differ in only one amino acid, and both showed similar transcriptional repression activities. Overexpression and RNA interference of in grape indicated that HSFB1 positively regulates the heat tolerance. Moreover, the heat tolerance of -overexpressing plants was positively correlated to expression level. The activity of the promoter is higher than that of under both normal and high temperatures. Promoter analysis showed that more TATA-box and AT~TATA-box -elements are present in the promoter than the promoter. The promoter sequence variations between and likely determine the expression levels that influence heat tolerance of the two grape germplasms with contrasting thermotolerance. Collectively, we validated the role of in heat tolerance, and the knowledge gained will advance our ability to breed heat-tolerant grape cultivars.