Comparative transcriptional profiling analysis of developing melon (Cucumis melo L.) fruit from climacteric and non-climacteric varieties

Abstract

BackgroundIn climacteric fruit-bearing species, the onset of fruit ripening is marked by a transient rise in respiration rate and autocatalytic ethylene production, followed by rapid deterioration in fruit quality. In non-climacteric species, there is no increase in respiration or ethylene production at the beginning or during fruit ripening. Melon is unusual in having climacteric and non-climacteric varieties, providing an interesting model system to compare both ripening types. Transcriptomic analysis of developing melon fruits from Védrantais and Dulce (climacteric) and Piel de sapo and PI 161375 (non-climacteric) varieties was performed to understand the molecular mechanisms that differentiate the two fruit ripening types.ResultsFruits were harvested at 15, 25, 35 days after pollination and at fruit maturity. Transcript profiling was performed using an oligo-based microarray with 75 K probes. Genes linked to characteristic traits of fruit ripening were differentially expressed between climacteric and non-climacteric types, as well as several transcription factor genes and genes encoding enzymes involved in sucrose catabolism. The expression patterns of some genes in PI 161375 fruits were either intermediate between. Piel de sapo and the climacteric varieties, or more similar to the latter. PI 161375 fruits also accumulated some carotenoids, a characteristic trait of climacteric varieties.ConclusionsSimultaneous changes in transcript abundance indicate that there is coordinated reprogramming of gene expression during fruit development and at the onset of ripening in both climacteric and non-climacteric fruits. The expression patterns of genes related to ethylene metabolism, carotenoid accumulation, cell wall integrity and transcriptional regulation varied between genotypes and was consistent with the differences in their fruit ripening characteristics. There were differences between climacteric and non-climacteric varieties in the expression of genes related to sugar metabolism suggesting that they may be potential determinants of sucrose content and post-harvest stability of sucrose levels in fruit. Several transcription factor genes were also identified that were differentially expressed in both types, implicating them in regulation of ripening behaviour. The intermediate nature of PI 161375 suggested that classification of melon fruit ripening behaviour into just two distinct types is an over-simplification, and that in reality there is a continuous spectrum of fruit ripening behaviour.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1649-3) contains supplementary material, which is available to authorized users.

Transcriptome analysis of the oriental melon (Cucumis meloL. var.makuwa) during fruit development

“…The sucrose content reaches a plateau in many melons. The sugar accumulation patterns of the oriental melon (PI161375; Sunghwan) were found to be similar to those of other melons except for a clear drop in the sucrose content during maturation (Saladie et al, 2015). This research suggested that the regulation of sugar metabolism differs between oriental melons and other types of melons.…”

“…This result suggests that sucrose is synthesized early in fruit development and used as a precursor for fructose or glucose. In a previous study, the level of sucrose was elevated during fruit maturation, and orthologs of sucrose synthase were detected, suggesting that multiple sucrose synthases were involved in sucrose synthesis during fruit maturation (Saladie et al, 2015). …”

“…5). In mature melon fruits, beta-carotene is the most abundant carotenoid, with trace amounts detected even in the white-fleshed Piel de sapo (Saladie et al, 2015). Our results corresponded to previous results and indicated that the expression patterns of carotenoid biosynthesis genes were regulated to increase the carotenoid contents during fruit maturation.…”

“…High levels of sucrose convey sweetness to the melon fruit (Burger et al, 2003; Villanueva et al, 2004). A previous study showed that the patterns of sugar accumulation during fruit maturation differed between the oriental melon and other melons (Saladie et al, 2015). The levels of glucose and fructose were similar among one oriental melon (Korean landrace Sunghwan, PI161375) and three other melons (Vedrantais, Dulce, and Piel de sapo).…”

“…With increasing interest in its biological properties and economic importance, the oriental melon has become an attractive model for studying valuable features, such as fruit morphology (Saladie et al, 2015), tissue specific RNA-seq (Cai, Wang & Pang, 2015; Cao et al, 2016; Kim et al, 2016b; Liu et al, 2016), pathogen resistance (Bezirganoglu et al, 2013), and understand the specialization of some genes involved in plant growth (Cai, Wang & Pang, 2015; Cao et al, 2016; Kim et al, 2016b; Liu et al, 2016). Despite these studies, the molecular mechanisms of fruit development in the oriental melon are still not elucidated.…”