Identification and Functional Analysis of the Gene Involved in Lignin Synthesis from "San Hong".

Overaccumulation of lignin (a physiological disorder known as granulation) often occurs during fruit ripening and postharvest storage in pomelo (). It causes an unpleasant fruit texture and taste. Previous studies have shown that lignin metabolism is closely associated with the process of juice sacs granulation. At present, the underlying transcriptional regulatory mechanisms remain unclear. In this study, we identified and isolated a candidate NAC transcription factor, , that is involved in the regulation of lignin biosynthesis in , which has homologs in and other plants. We used the fruit juice sacs of 'San hong' as the material, the staining for lignin with HCl-phloroglucinol of fruit juice sacs became dark red from the various developmental stages at 172 to 212 days post anthesis (DPA). The RT-qPCR was used to analyze the gene expression of and its target gene in fruit sacs, it was found that the expression trend of was basically same as , which increased gradually and peaked at 212 DPA. The expression level of in juice sacs obtained away from the core was the lowest, while those near the core and granulated area were highly expressed. The transcriptional activation activity of and was analyzed by a yeast two-hybrid system, with only showing transcriptional activation activity in Y2H Gold yeast. A transformation vector, p1301- , was transformed into the mesocarp of 'San hong' by -mediated transformation. Results showed that the expression of transcription factors and are all upregulated. Further experiments proved that not only can directly trans-activate the promoter of but also trans-activate the promoters for the lignin biosynthesis-related genes and by dual luciferase assay. We isolated the gene in pomelo and found regulates target genes conferring the regulation of juice sacs granulation.