Identification of key gene networks controlling monoterpene biosynthesis during grape ripening by integrating transcriptome and metabolite profiling

Monoterpenes are typical aroma components of muscat grape cultivars,providing pleasant floral and fruity aromas to grapes and wines.However,the molecular mechanism of monoterpene biosynthesis between muscat and non-muscat grape remains unclear.Here,the muscat grape cultivar‘Jumeigui’and the non-muscat grape cultivar‘Kyoho’were chosen as plant materials for a comprehensive transcriptome and metabolite analysis.The gas chromatography-mass spectrometry(GC-MS)analysis demonstrated that a total of 27 and 23 monoterpene compounds were identified and quantified in the‘Jumeigui’and‘Kyoho’grape,respectively.‘Jumeigui’grape accumulated significantly higher concentrations of monoterpenes than‘Kyoho’grape.Furthermore,geraniol,linalool,geranic acid,and β-citronellol might be important odorants contributing to the floral character of the‘Jumeigui’grape due to the high levels odor activity values(OAVs).Transcriptome analysis demonstrated that the expression profiles of VvDXS,VvGGPPS.SSU1,Vv TPS-b/g showed a positive correlation with monoterpene accumulation in grapes.In addition,the expression patterns of the genes involved in jasmonic acid(JA)synthesis and signal were also positively correlated with monoterpene accumulation.All these results will help guide the functional verification of candidate genes related to monoterpene biosynthesis,as well as identify the master transcriptional and hormonal regulators of this pathway in grapes.

Differential gene expression analysis of ‘Chili’ (Pyrus bretschneideri) fruit pericarp with two types of bagging treatments

Preharvest bagging is a simple,grower-friendly and safe physical protection technique commonly applied to many fruits,and the application of different fruit bags can have various effects.To explore the molecular mechanisms underlying the fruit quality effects of different bagging treatments,digital gene expression(DGE)profiling of bagged and unbagged‘Chili’(Pyrus bretschneideri Rehd.)pear pericarp during development was performed.Relative to unbagged fruit,a total of 3022 and 769 differentially expressed genes(DEGs)were detected in the polyethylene(PE)-bagged and non-woven fabric-bagged fruit,respectively.DEGs annotated as photosynthesis-antenna proteins and photosynthesis metabolism pathway were upregulated in non-woven fabric-bagged fruit but downregulated in the PE-bagged fruit.Non-woven fabric bagging inhibited lignin synthesis in‘Chili’pear pericarp by downregulating DEGs involved in phenylpropanoid biosynthesis;consequently,the fruit lenticels in non-woven fabric-bagged fruit were smaller than those in the other treatments.The results indicate that the non-woven fabric bagging method has a positive effect on the appearance of‘Chili’pear fruit but neither of the two bagging treatments is conducive to the accumulation of soluble sugar.

An apple (Malus domestica) AP2/ERF transcription factor modulates carotenoid accumulation

Color is an important trait for horticultural crops.Carotenoids are one of the main pigments for coloration and have important implications for photosynthesis in plants and benefits for human health.Here,we identified an APETALA2(AP2)/ETHYLENE RESPONSE FACTOR(ERF)transcription factor named MdAP2-34 in apple(Malus domestica Borkh.).MdAP2-34 expression exhibited a close correlation with carotenoid content in‘Benin Shogun’and‘Yanfu 3’fruit flesh.MdAP2-34 promotes carotenoid accumulation in MdAP2-34-OVX transgenic apple calli and fruits by participating in the carotenoid biosynthesis pathway.The major carotenoid contents of phytoene andβ-carotene were much higher in overexpressing MdAP2-34 transgenic calli and fruit skin,yet the predominant compound of lutein showed no obvious difference,indicating that MdAP2-34 regulates phytoene andβ-carotene accumulation but not lutein.MdPSY2-1(phytoene synthase 2)is a major gene in the carotenoid biosynthesis pathway in apple fruit,and the MdPSY2-1 gene is directly bound and transcriptionally activated by MdAP2-34.In addition,overexpressing MdPSY2-1 in apple calli mainly increases phytoene and total carotenoid contents.Our findings will advance and extend our understanding of the complex molecular mechanisms of carotenoid biosynthesis in apple,and this research is valuable for accelerating the apple breeding process.