Abstract：NAC (petunia NAM and Arabidopsis thaliana ATAF1, ATAF2, and CUC2) transcription factors play important regulatory roles in plant secondary wall thickening. In order to explore the function and molecular mechanism of NAC transcription factor in the formation of secondary wall of tartary buckwheat (Fagopyrum tataricum), reverse transcription PCR (RT-PCR) was used to clone a candidate NAC transcription factor previously identified by comparative transcriptome, named FtNAC16, which might be involved in regulating the synthesis of secondary wall of tartary buckwheat shell cells. Then the bioinformatics, subcellular localization and gene expression analysis of FtNAC16 were conducted. As results, the CDS length of FtNAC16 (GenBank No. OR723785) was 1 086 bp and it encoded 361 amino acids. Multiple sequence alignment and phylogenetic tree analysis indicated that FtNAC16 belonged to the NAC transcription factor family and was closely related to AtNST2 (NAC secondary wall thickening), which regulated secondary wall thickening in Arabidopsis thaliana. Subcellular localization showed that FtNAC16 was located in the nucleus. Gene expression analysis suggested that FtNAC16 was highly expressed in roots, stems, flowers and early developing grains with high cellulose content. In addition, the expression analysis of FtNAC16 in thick shell tartary buckwheat and thin shell tartary buckwheat at different developmental stages showed a similar expression pattern, with a trend of increasing and then decreasing, and the highest expression was observed at 7 d after pollination. However, the expression of FtNAC16 in thick shell tartary buckwheat was significantly higher than that in thin shell tartary buckwheat at early stage of development. Further expression analysis revealed that the expression of the downstream regulatory gene FtMYB103, cellulose synthase 4 (FtCESA4) and FtCESA8 involved in cellulose synthesis were highly positively correlated with FtNAC16 in the grains of thick shell tartary buckwheat and thin shell tartary buckwheat at different developmental stages. All these results suggested that FtNAC16 was a nucleo-specific NAC transcription factor, which may positively regulate the biosynthesis of secondary walls by positively regulating the expression of genes further related to the biosynthesis of cell secondary walls of tartary buckwheat in different tissue parts, especially in the fruit shell cells. It provides excellent genetic resources and theoretical basis for breeding new varieties of buckwheat with high yield, high quality and strong adaptability.
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