Genome-Wide Analysis and Expression Patterns of NAC Transcription Factor Family Under Different Developmental Stages and Abiotic Stresses in Chinese Cabbage

NAC (NAM, ATAF1/2 and CUC2) proteins represent a major plant-specific transcription factor (TF) family and are expressed in various developmental stages and tissues. In this study, 204 NAC genes, including 17 membrane-bound TFs, were identified in the Brassica rapa (Chinese cabbage) genome. The gene structure and motif compositions obtained suggest that the BrNAC gene family is classified broadly into eight groups. The predicted Chinese cabbage NAC genes were distributed in ten chromosomes at various densities but mainly in chromosomes 3 and 10 (14 and 14 %, respectively). A comprehensive analysis of NAC family genes in Chinese cabbage, rice and Arabidopsis was also performed. Phylogenetic analysis of BrNACs, along with their Arabidopsis and rice counterparts, divided the proteins into two major groups (A and B) and 19 subgroups. Homologous, paralogous, and orthologous searches of Chinese cabbage and Arabidopsis revealed gene loss during genome triplication in Chinese cabbage. Finally, the expression of 55 selected Chinese cabbage BrNAC genes was analyzed under different developmental stages and abiotic stress conditions (heat, cold, ABA, GA, and PEG). The selected genes were classified into three types (constitutive expression, no-expression, and period-specific expression) according to their expression profiles, which indicate that the NAC genes are involved in various aspects of the physiological and developmental processes of Chinese cabbage. Under different abiotic stress conditions, several members of BrNACs were upregulated by various abiotic stresses. Our study provides a very useful reference for functional analysis of members of BrNAC gene family in Chinese cabbage.