Genome-Wide Analysis of the Hsf Family and Functional Characterization of CiHsf10 Under Low-Temperature Stress in Chrysanthemum indicum.

To improve Chrysanthemum tolerance to low temperatures and its adaptability to low autumn temperatures in Northeast China, we conducted the first genome-wide identification of the heat shock transcription factors (Hsfs) in Chrysanthemum indicum under low-temperature stress. Based on genome-wide analyses, we identified 14 CiHsf genes in Chrysanthemum indicum. Based on structural characteristics, the genes were grouped into two subfamilies, comprising 10 HsfA and four HsfB members, with no representatives of the HsfC subfamily detected. CiHsf1~CiHsf14 were located on seven chromosomes, and their promoter regions harbored numerous cis-acting elements associated with responses to low temperature, hormones, and light. Tissue-specific expression profiling revealed that seven CiHsf genes were predominantly expressed in roots, two in stems, three in leaves, and two in flowers. The analysis of low-temperature expression characteristics showed that CiHsf2, CiHsf5, CiHsf8, and CiHsf10 were significantly upregulated following cold acclimation, indicating that these genes may participate in the low-temperature response mechanism of Chrysanthemum indicum. Here, we demonstrated that transient transformation of Chrysanthemum indicum with 35S:CiHsf10 reduced reactive oxygen species (ROS) accumulation under low-temperature stress, which may contribute to enhanced cold tolerance.