Genome-wide identification, classification and expression analysis of NAC family of genes in sorghum [ Sorghum bicolor (L.) Moench]

NAC transcription factors are involved in many biological processes via regulation of downstream target gene expression and play essential roles in regulation of plant growth and improving plant tolerance to abiotic stress. NAC transcription factors have been studied in various species, but little information is available regarding these factors in sorghum. Genome-wide investigation of potentially abiotic stress related sorghum NAC-type genes was performed. A total of 145 non-redundant NAC genes ( SbNAC1 – SbNAC145 ) were identified in the sorghum genome. These genes were distributed unevenly across the 10 chromosomes, and were divided into 16 groups based on sequence similarity. Gene structure analysis indicated that most SbNAC genes contained three exons and two introns, and had ten putative conserved motifs. Phylogenetic analysis indicated that the SbNAC genes with similar motif distributions were clustered into the same branch. Seven SbNAC genes, which were grouped into the stress-related subgroup, were isolated and have been confirmed to have transcriptional activity in yeast. SbNAC genes showed differential expression patterns over time in response to dehydration, salinity, cold, and phytohormone abscisic acid stress treatments, thus suggesting essential roles in plant responses to abiotic stress. In the germination stage, SbNAC56 overexpression transgenic lines exhibited significantly enhanced hypersensitivities to ABA, NaCl and d -Mannitol. This may infer that SbNAC56 may play essential roles in plants response to abiotic stresses in ABA dependent signaling pathway. Here, we present a comprehensive overview of the SbNAC genes and provide a foundation for future functional research regarding their biological roles in sorghum stress tolerance, even in the regulation of plant growth.