Genomewide identification, classification and analysis of NAC type gene family in maize

NAC transcription factors comprise a large plant-specific gene family. Increasing evidence suggests that members of this family have diverse functions in plant growth and development. In this study, we performed a genomewide survey of NAC type genes in maize (Zea mays L.). A complete set of 148 nonredundant NAC genes (ZmNAC1-ZmNAC148) were identifiedin the maize genome using Blast search tools, and divided into 12 groups (a-l) based on phylogeny. Chromosomal location of these genes revealed that they are distributed unevenly across all 10 chromosomes. Segmental and tandem duplication contributed largely to the expansion of the maize NAC gene family. The Ka/Ks ratio suggested that the duplicated genes of maize NAC family mainly experienced purifying selection, with limited functional divergence after duplication events.Microarray analysis indicated most of the maize NAC genes were expressed across different developmental stages. Moreover,19 maize NAC genes grouped with published stress-responsive genes from other plants were found to contain putative stress-responsive cis-elements in their promoter regions. All these stress-responsive genes belonged to the group d (stress-related).Further, these genes showed differential expression patterns over time in response to drought treatments by quantitative real-time PCR analysis. Our results reveal a comprehensive overview of the maize NAC, and form the foundation for future functional research to uncover their roles in maize growth and development.