Genome-wide identification, classification, and expression analysis of sHSP genes in Chinese cabbage (Brassica rapa ssp pekinensis).

Small heat shock proteins (sHSPs) are essential for the plant's normal development and stress responses, especially the heat stress response. The information regarding sHSP genes in Chinese cabbage (Brassica rapa ssp pekinensis) is sparse, hence we performed a genome-wide analysis to identify sHSP genes in this species. We identified 26 non-redundant sHSP genes distributed on all chromosomes, except chromosome A7, with one additional sHSP gene identified from an expressed sequence tag library. Chinese cabbage was found to contain more sHSP genes than Arabidopsis. The 27 sHSP genes were classified into 11 subfamilies. We identified 22 groups of sHSP syntenic orthologous genes between Chinese cabbage and Arabidopsis. In addition, eight groups of paralogous genes were uncovered in Chinese cabbage. Protein structures of the 27 Chinese cabbage sHSPs were modeled using Phyre2, which revealed that all of them contain several conserved ß strands across different subfamilies. In general, gene structure was conserved within each subfamily between Chinese cabbage and Arabidopsis, except for peroxisome sHSP. Analysis of promoter motifs showed that most sHSP genes contain heat shock elements or variants. We also found that biased gene loss has occurred during the evolution of the sHSP subfamily in Chinese cabbage. Expression analysis indicated that the greatest transcript abundance of most Chinese cabbage sHSP genes was found in siliques and early cotyledon embryos. Thus, genome-wide identification and characterization of sHSP genes is a first and important step in the investigation of sHSPs in Chinese cabbage.

Genome-wide identification, classification, and analysis of heat shock transcription factor family in Chinese cabbage (Brassica rapa pekinensis).

Chinese cabbage (Brassica rapa ssp. pekinensis) is one of the most important vegetable crops grown worldwide, and various methods exist for selection, propagation, and cultivation. The entire Chinese cabbage genome has been sequenced, and the heat shock transcription factor family (Hsfs) has been found to play a central role in plant growth and development and in the response to biotic and abiotic stress conditions, particularly in acquired thermotolerance. We analyzed heat tolerance mechanisms in Chinese cabbage. In this study, 30 Hsfs were identified from the Chinese cabbage genome database. The classification, phylogenetic reconstruction, chromosome distribution, conserved motifs, expression analysis, and interaction networks of the Hsfs were predicted and analyzed. Thirty BrHsfs were classified into 3 major classes (class A, B, and C) according to their structural characteristics and phylogenetic comparisons, and class A was further subdivided into 8 subclasses. Distribution mapping results showed that Hsf genes were located on 10 Chinese cabbage chromosomes. The expression profile indicated that Hsfs play differential roles in 5 organs in Chinese cabbage, and likely participate in the development of underground parts and regulation of reproductive growth. An orthologous gene interaction network was constructed, and included MBF1C, ROF1, TBP2, CDC2, and HSP70 5 genes, which are closely related to heat stress. Our results contribute to the understanding of the complexity of Hsfs in Chinese cabbage and provide a basis for further functional gene research.