Transcriptional and epigenetic analysis reveals that NAC transcription factors regulate fruit flavor ester biosynthesis

Abstract

Flavor-associated volatile chemicals make major contributions to consumers' perception of fruits. Although great progress has been made in establishing the metabolic pathways associated with volatile synthesis, much less is known about the regulation of those pathways. Knowledge of how those pathways are regulated would greatly facilitate efforts to improve flavor. Volatile esters are major contributors to fruity flavor notes in many species, providing a good model to investigate the regulation of volatile synthesis pathways.Here we initiated a study of peach (Prunus persica L. Batsch) fruits, and identified that the alcohol acyltransferase PpAAT1 contributes to ester formation. We next identified the transcription factor (TF) PpNAC1 as an activator of PpAAT1 expression and ester production. These conclusions were based on in vivo and in vitro experiments and validated by correlation in a panel of 30 different peach cultivars. Based on homology between PpNAC1 and the tomato (Solanum lycopersicum) TF NONRIPENING (NOR), we identified a parallel regulatory pathway in tomato. Overexpression of PpNAC1 enhances ripening in a nor mutant and restores synthesis of volatile esters in tomato fruits. Furthermore, in the NOR-deficient mutant tomatoes generated by CRISPR/Cas9, lower transcript levels of SlAAT1 were detected. The apple (Malus domestica) homolog MdNAC5 also stimulates MdAAT1 expression via binding to this gene's promoter. In addition to transcriptional control, epigenetic analysis showed that increased expression of NACs and AATs is associated with removal of the repressive mark H3K27me3 during fruit ripening. Our results support a conserved molecular mechanism in which NAC TFs activate ripening-related AAT expression, which in turn catalyzes volatile ester formation in multiple fruit species.

Genome-Wide Identification of NAC Transcription Factor Family in Juglans mandshurica and Their Expression Analysis during the Fruit Development and Ripening

“…A lot of attention has been paid to the role of the NAC gene family members during fruit development and ripening. A recent study found that PpNAC1 regulated the expression of ripening-related PpAAT1 and contributed to volatile ester formation in Prunus persica [60], indicating a key role during fruit ripening. In papaya (Carica papaya), CpNAC1 was reported to regulate carotenoid accumulation during fruit ripening [61].…”

GC-MS Metabolite and Transcriptome Analyses Reveal the Differences of Volatile Synthesis and Gene Expression Profiling between Two Apple Varieties

“…Moreover, in banana, MabZIP4 and MabZIP5 were capable of binding directly to BanAAT promoter, suggesting the function of MabZIPs in controlling aroma production [ 42 ]. Additionally, the transcription factor PpNAC1 was proved to transcriptionally activate the PpAAT1 gene and formation of volatile esters in peaches [ 44 ]. AP2/ERF transcription factors have been shown to be associated with the production of volatile terpenes in sweet orange fruits [ 45 ].…”

NAC Transcription Factor Family Regulation of Fruit Ripening and Quality: A Review

“…In peach fruits (Prunus persica), PpNAC1 promotes the biosynthesis of volatile esters during fruit ripening by directly binding to the promoter region of alkyl transferase alcohol acyltransferase 1 (PpAAT1) and activating its expression. This pathway is downstream of ethylene signal and conserved in tomato (SlNOR-SlAAT1) and apple fruit (MdNAC5-MdAAT1) [144].…”