Genome-wide identification of heat shock factors in Myricaria laxiflora and their response to abiotic stresses.

Myricaria laxiflora is a rare and endangered shrub in China, and its wild populations are threatened by diverse abiotic stresses. Heat shock factors (HSFs) are essential for coping with environmental stresses, however, information about HSFs in M. laxiflora is limited. Currently, a total of 21 MlHSFs were systematically detected in the latest released genome of M. laxiflora. The MlHSFs were assigned into three subgroups (i.e., A, B and C) according to their conserved protein domains. All the MlHSFs were predicted to localize in nucleus with the conserved HSF-type DNA-binding domain, suggesting their potential roles as transcription factors. MlHSF proteins from the same subgroup shared similar conserved protein domains, the variable C-terminal domains of HSF proteins implied their functional diversity. A total of six gene duplication events from the same subgroup were detected among the HSF gene members, and all the duplication events belonged to segmental duplication. Furthermore, plenty of cis-elements were detected upstream of HSF gene members, these cis-elements could be primarily categorized into light response, as well as stress and hormone response. Transcriptomic analysis showed that most MlHSFs were significantly inhibited by cadmium and waterlogging stresses in most cases, however, MlHSFC1 was significantly stimulated by both cadmium and waterlogging stresses in M. laxiflora. A comprehensive co-expression network of MlHSFs has been established to reveal the potential roles of MlHSFs in photosynthesis, redox homeostasis and protein folding under abiotic stresses. The results obtained suggested the crucial roles of MlHSFs in adapting to environmental stresses in M. laxiflora.