Transcriptomic and metabolomic analysis of on-tree fruit maturation in the white, melting-flesh peach cultivar ‘Lemonato’

The impact of different maturity levels of peaches on fruit quality, metabolic pattern and transcriptomic alternation was studied. To achieve this, ‘Lemonato’ peaches were sampled at commercial harvest time and then were separated based on their peel ground color into immature (light green exocarp), semi-mature (partly yellow exocarp) and mature (entirely yellow exocarp). Data indicated that several key maturity parameters, such as color index, fruit firmness, chlorophyll content, dry matter, total phenol content and antioxidant activity were notably induced by the maturity transition. Consistent with this observation, increased levels of phenolic compounds, including catechin, epicatechin, procyanidin B1/B2/B4 and chlorogenic acid, were identified at the last maturity stage. Mature fruit was also characterized by an elevated abundance of various primary metabolites (e.g. sorbitol, arabinose, xylose) and decreased levels of main organic acids and putrescine. Genes predominantly associated with flavonoid biosynthesis, calcium signaling, cell wall integrity, auxin metabolism, and aquaporins and chloroplast function were remarkably affected by maturity. Several genes were also identified (e.g. EXORDIUM, PCC13-62 and SDI1), including transcription factors, such as IBH1, homeobox ATHB-13 and bHLH63, undergoing major changes during fruit maturation. These results enhance understanding of on-tree metabolic and transcriptomic events that coordinate peach fruit maturation, helping to identify the optimal harvest time for best peach fruit quality