Transcriptomic and Metabolomic Studies Reveal Mechanisms of Effects of CPPU-Mediated Fruit-Setting on Attenuating Volatile Attributes of Melon Fruit

Abstract

N1-(2-chloro-4-pyridyl)-N3-phenylurea (CPPU), a synthetic cytokinin-active compound, is widely applied to induce parthenocarpic fruit set and enhance melon fruit enlargement (Cucumis melo L.). CPPU may also influence fruit quality; however, the mechanisms through which this occurs remain unknown. We investigated the differences in volatile emissions between parthenocarpic fruit set by CPPU (C) and seeded fruit set by artificial pollination (P). Gas chromatography–mass spectrometry (GC–MS) analysis revealed that six volatile organic compounds (VOCs) emitted by the P-group fruits were not detected in C-group fruits. The relative abundances of another 14 VOCs emitted by the CPPU-treated fruits were less than those in the P-group fruits. RNA sequencing analysis indicated that a total of 1027, 994, and 743 differentially expressed genes (DEGs) were detected in the C20 (treatment with 20 mg·L–1 CPPU) vs. P, P-C20 (pollination followed by 20 mg·L−1 CPPU treatment) vs. P, and P-C20 vs. C20 treatments, respectively. Compared with the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, the DEGs related to fatty acid degradation and metabolism, which contribute to volatile production, were enriched. In particular, DEGs such as carotenoid cleavage dioxygenase (CCD)-, lipoxygenase (LOX)-, alcohol dehydrogenase (ADH)-, and alcohol acyltransferase (ATT)-related genes were closely related to the formation of volatiles. In summary, our study provides a metabolic and transcriptomic atlas, reveals the impact of CPPU on VOCs, and enhances our understanding of the mechanisms of CPPU that contribute towards generally reducing the quality of melon fruit.

CPPU Improves Fruit Setting and Growth in Greenhouse-grown Oriental Melons (Cucumis melo L. var. makuwa Makino)

“…NS, *, **, ***Nonsignificant or significant P # 0.05, 0.01, or 0.001, respectively. Our results regarding the effects of CPPU on fruit quality are inconsistent with those of Li et al (2021); this disparity may be attributable to differences in the type of melon species or cultivar used in the two studies. Some studies have reported that CPPU treatment reduced the levels of sucrose and glucose in oriental melons (Luo et al 2020;Wang et al 2023).…”

“…High concentrations of exogenous CPPU may negatively affect fruit quality; in particular, the biosynthesis and accumulation of Cu B within melons may increase the level of bitterness (Hayata et al 2000;Li et al 2021). Transcriptional analyses revealed that the expression of genes involved in the biosynthesis of Cu B (CmBi, Cm710, and CmACT) and a fruit-specific transcription factor (CmBt) was significantly induced by 20 mg•L À1 CPPU (Luo et al 2020).…”

Discrimination and Characterization of Volatile Flavor Compounds in Fresh Oriental Melon after Forchlorfenuron Application Using Electronic Nose (E-Nose) and Headspace-Gas Chromatography-Ion Mobility Spectrometry (HS-GC-IMS)

“…On the contrary, 2-methylbutanol imparts an alcoholic flavor, and 2-butanone possesses an ethereal fruity odor, which were significantly lower in the three forchlorfenuron application groups. A previous study showed that forchlorfenuron application could significantly influence the volatile flavor compounds in muskmelon [ 14 ]. The relative abundances of 14 volatile compounds emitted by the forchlorfenuron-treated fruits declined, including six ethyl esters, four aldehydes, three alcohols, and one ketone.…”

“…The volatile components of melon have been analyzed in previous reports, and approximately 300 compounds have been identified [ 8 , 9 , 10 , 11 ]. They produce volatile aldehydes, alcohols, and especially large quantities of esters, likely to be the key contributors to their unique aroma [ 12 , 13 , 14 ]. However, limited studies have reported the effect of forchlorfenuron on the aroma compounds of oriental melon fruit.…”

Function-driven design of Bacillus kochii and Filobasidium magnum co-culture to improve quality of flue-cured tobacco

“…It has been confirmed that the oxidative degradation of carotenoids in plants involves dioxygenases and that lipoxygenase (LOX, EC 1.13.11.12) plays a significant role in this process ( Lyu et al, 2021 ). LOX is also regarded as a critical enzyme in fatty acid metabolism, one of the main pathways for synthesizing aromas or flavors in fruits ( Li et al, 2021 ). Therefore, it is expected that the screened strains with high LOX incorporated with B. kochii SC to produce good quality-enhancing effects.…”