Molecular characterization and functional roles of NAC transcription factors in regulating chlorophyll degradation during litchi fruit ripening

Abstract

NAC (NAM, ATAF1/2 and CUC) transcription factors represent one of the largest plant specific transcription factor families, playing crucial roles in plant growth and development. Chlorophyll, a vital pigment in plant photosynthesis, diminishes during fruit ripening and plant senescence. In this study, we identified 114 NAC genes from the litchi genome. LcNACs were found to be clustered, paired, and independently distributed on chromosomes, and classified into 7 groups. Collinearity analysis revealed that 15 gene pairs, involving 26 LcNACs, resulted from segmental duplication events. Based on transcriptome data, clustering and correlation analysis, LcNAC025, LcNAC038, and LcNAC087 were identified as key players in chlorophyll degradation. As transcriptional activators located in the nucleus, they were shown to directly bind to the promoters of LcNYC, LcPAO, and LcSGR, activating their expression. Moreover, transient overexpression of LcNAC025, LcNAC038, and LcNAC087 in tobacco leaves promoted chlorophyll degradation and up-regulated the expression of NbNYC, NbPPH, NbPAO, and NbSGR. In summary, this study highlights the molecular roles of LcNAC025, LcNAC038, and LcNAC087 in regulating chlorophyll degradation during litchi fruit ripening.