Abstract

Overaccumulation of lignin (a physiological disorder known as granulation) often occurs during fruit ripening and postharvest storage in pomelo (Citrus grandis). 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,CgNAC043, that is involved in the regulation of lignin biosynthesis inCitrus grandis, which has homologs inArabidopsisand 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 ofCgNAC043and its target geneCgMYB46in fruit sacs, it was found that the expression trend ofCgNAC043was basically same asCgMYB46, which increased gradually and peaked at 212 DPA. The expression level ofCgNAC043in 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 ofCgNAC043andCgMYB46was analyzed by a yeast two-hybrid system, with onlyCgNAC043showing transcriptional activation activity in Y2H Gold yeast. A transformation vector, p1301-CgNAC043, was transformed into the mesocarp of ‘San hong’ byAgrobacterium-mediated transformation. Results showed that the expression of transcription factorsCgMYB58andCgMYB46are all upregulated. Further experiments proved thatCgNAC043not only can directly trans-activate the promoter ofCgMYB46but also trans-activate the promoters for the lignin biosynthesis-related genesCgCCoAOMTandCgC3Hby dual luciferase assay. We isolated theCgNAC043gene in pome