Genome-Wide Identification of NAC Genes Associated with Bast Fiber Growth in Ramie (Boehmeria nivea L.)

NAM, ATAF, and CUC (NAC) proteins are plant-specific transcription factors that play crucial roles in fiber growth by regulating the secondary wall thickening. In this study, a systematical investigation of NAC genes was performed in the genome of ramie, an important fiber crop, resulting in a total of 60 ramie NAC genes identified. Phylogenetic analysis of these 60 NAC members in conjunction with 111 Arabidopsis NAC proteins identified 11 subfamilies, three of which showed considerable contraction in the ramie genome. Ten ramie NAC genes were identified to encode the orthologs of Arabidopsis NAC regulators involved in the control of secondary wall biosynthesis. Of these ten genes, most showed relatively high expression in the stems, and eight displayed a differential expression between the barks from the top and middle section of the stems where fiber growth is under different stages. Furthermore, the overexpression of three of these ten NAC genes significantly promoted fiber growth in transgenic Arabidopsis. These results indicated that these ten NAC genes were associated with the fiber growth of ramie. This study provided an important basis for researching the regulatory mechanism of fiber growth.