A comprehensive analysis of <i>NAC</i> gene family in <i>Oryza sativa japonica:</i> a structural and functional genomics approach

<i>NAC</i> gene family regulates diverse aspects of plant growth and developmental processes. The NAC DNA binding domains together with cis-acting elements play inter-related roles in regulating gene expression. In this study, an <i>in silico</i> approach for genome wide analysis of <i>NAC</i> gene in <i>Oryza sativa japonica</i> lead to an identification of 11 <i>NAC</i> genes, distributed over 12 chromosomes. A detailed analysis of phylogenetic relationship, motifs, gene structure, duplication patterns, positive-selection pressure and cis-elements of 11 <i>OsNAC</i> genes were performed. Three pairs of <i>NAC</i> genes with a high degree of homology in terminal nodes were observed and were inferred to be paralogous pairs. One conserved NAC domain was analyzed in all the NAC proteins. Only one gene was studied to be intronless and the majority had 2 introns. Segmental gene duplication pattern was predominant in 11 <i>NAC</i> genes. Ka/Ks ratio of 3 pairs of segmentally duplicated gene was substantially lower than 1, suggesting that the <i>OsNAC</i> sequences are under strong purifying selection pressure. <i>NAC74</i> and <i>NAC71</i> gene showed the maximum responsiveness for several factors. The paralogous genes, <i>NAC2</i> and <i>NAC67</i> were found to have maximum mya values, respectively. They showed maximum difference amongst themselves in all the categories of responsiveness. Responsiveness towards abscisic acid was observed to be absent in <i>NAC67</i>, but present in <i>NAC2</i>, while responsiveness to meristem inducibility was observed to remain absent in <i>NAC2</i> but present in <i>NAC67</i>. These results would provide a platform for the future identification and analysis of <i>NAC</i> genes in <i>Oryza sativa japonica</i>. Communicated by Ramaswamy H. Sarma