CarHSFB2, a Class B Heat Shock Transcription Factor, Is Involved in Different Developmental Processes and Various Stress Responses in Chickpea (Cicer Arietinum L.)

Heat shock transcription factor (HSF) plays an essential role on the increased tolerance against heat stress by regulating the expression of heat-responsive genes. In this study, a HSF gene, CarHSFB2, was isolated and characterized in chickpea. CarHSFB2 was a nuclear protein with a predicted polypeptide of 267 amino acids and encoded by a single/low copy genes. Phylogenetic analysis showed that CarHSFB2 belonged to the class B HSFs. It had little or no any transcription activation activity due to lack of aromatic, hydrophobic, and acidic amino acid (AHA) motifs. CarHSFB2 showed different expression patterns among different developmental processes (leaf senescence, developing seed, and embryo of germinating seed). It was induced by the stress of heat, salt, wound and drought, and the treatment of H2O2, IAA, and GA3, respectively, while inhibited by 6-BA. However, the other stress and chemical treatments (cold, ABA, MeJA, Et, and SA) had no obvious effect on its expression. Overexpression of CarHSFB2 in Arabidopsis seedlings showed the increased tolerance to drought and heat stress. Additionally, stress-responsive genes, RD22, RD26, and RD29A, showed significantly higher expression levels in transgenic Arabidopsis seedlings than in the wild type (WT) under drought stress, whereas HsfA2, HsfB2a, and HsfA7a in transgenic Arabidopsis seedlings were markedly accumulated in transcript level than in the WT under heat stress. All these results indicate that CarHSFB2, a class B HSF, positively functions in different developmental processes and various stress responses, especially in positive response to heat and drought stresses, in chickpea.