Molecular Cloning, Expression Profiles, Characterization and Function of a Novel Small Heat Shock Protein (HbsHSP23.8a) in Hevea brasiliensis

Small heat shock proteins (sHSPs) are involved in a wide range of abiotic stresses, yet the functional roles of sHSP family genes in rubber tree salt tolerance remain largely uncharacterized. In this study, HbsHSP23.8a, a novel sHSP gene from rubber tree, was cloned and analyzed in detail. HbsHSP23.8a consists of a targeting peptide, an N-terminal domain, an α-crystallin domain (ACD), and C-terminal extensions. Additionally, putative dimer interface and conserved amino acid sequences were identified in the ACD and N-terminal domain of HbsHSP23.8a, respectively. HbsHSP23.8a transcripts were detected in different tissues and developmental stages of leaves, indicating that HbsHSP23.8a was associated with rubber tree growth and development. Besides tapping panel dryness (TPD), HbsHSP23.8a was also involved in low-temperature, high-salt, methyl jasmonate (MeJA), and ethephon (ET) responses. Under salt stress, overexpression of HbsHSP23.8a in transgenic tobacco plants exhibited greater plant height and fresh weight than wild-type (WT) plants. In addition, tobacco plants overexpressing HbsHSP23.8a increased the activities of antioxidant enzymes and decreased hydrogen peroxide (H2O2) accumulation and chlorophyll degradation under salt stress compared with the WT plants. Collectively, our results suggest that HbsHSP23.8a is related to rubber tree growth, TPD, leaf development, stress and hormone responses. Furthermore, heterologous expression of HbsHSP23.8a is associated with enhanced salt tolerance in transgenic tobacco, which may be attributed to elevated antioxidant enzyme activities, reduced cellular H2O2 accumulation, and alleviated chlorophyll degradation.