Comprehensive Analysis of the Hsp20 Gene Family in Canavalia rosea Indicates Its Roles in the Response to Multiple Abiotic Stresses and Adaptation to Tropical Coral Islands

Heat shock protein 20 (Hsp20) is a major family of heat shock proteins that mainly function as molecular chaperones and are markedly accumulated in cells when organisms are subjected to environmental stress, particularly heat. Canavalia rosea is an extremophile halophyte with good adaptability to environmental high temperature and is widely distributed in coastal areas or islands in tropical and subtropical regions. In this study, we identified a total of 41 CrHsp20 genes in the C. rosea genome. The gene structures, phylogenetic relationships, chromosome locations, and conserved motifs of each CrHsp20 or encoding protein were analyzed. The promoters of CrHsp20s contained a series of predicted cis-acting elements, which indicates that the expression of different CrHsp20 members is regulated precisely. The expression patterns of the CrHsp20 family were analyzed by RNA sequencing both at the tissue-specific level and under different abiotic stresses, and were further validated by quantitative reverse transcription PCR. The integrated expression profiles of the CrHsp20s indicated that most CrHsp20 genes were greatly upregulated (up to dozens to thousands of times) after 2 h of heat stress. However, some of the heat-upregulated CrHsp20 genes showed completely different expression patterns in response to salt, alkaline, or high osmotic stresses, which indicates their potential specific function in mediating the response of C. rosea to abiotic stresses. In addition, some of CrHsp20s were cloned and functionally characterized for their roles in abiotic stress tolerance in yeast. Taken together, these findings provide a foundation for functionally characterizing Hsp20s to unravel their possible roles in the adaptation of this species to tropical coral reefs. Our results also contribute to the understanding of the complexity of the response of CrHsp20 genes to other abiotic stresses and may help in future studies evaluating the functional characteristics of CrHsp20s for crop genetic improvement.