Transcriptome analysis provides insights into the regulation of metabolic processes during postharvest cold storage of loquat(Eriobotrya japonica)fruit

Loquat(Eriobotrya japonica)fruit accumulates lignin during postharvest storage under chilling conditions(0℃),while low-temperature conditioning(LTC;5℃for 6 days followed by transfer to 0℃)or heat treatment(HT;40℃for 4 h followed by transfer to 0℃)can alleviate lignification.Here we compared transcriptome profiles of loquat fruit samples under LTC or HT to those stored at 0℃at five time points from day 1 to day 8 after treatment.High-throughput transcriptome sequences were de novo assembled into 53,319 unique transcripts with an N50 length of 1306 bp.A total of 2235 differentially expressed genes were identified in LTC,and 1020 were identified in HT compared to 0℃.Key genes in the lignin biosynthetic pathway,including EjPAL2,EjCAD1,EjCAD3,4CL,COMT,and HCT,were responsive to LTC or HT treatment,but they showed different expression patterns during the treatments,indicating that different structural genes could regulate lignification at different treatment stages.Coexpression network analysis showed that these candidate biosynthetic genes were associated with a number of transcription factors,including those belonging to the AP2,MYB,and NAC families.Gene ontology(GO)enrichment analysis of differentially expressed genes indicated that biological processes such as stress responses,cell wall and lignin metabolism,hormone metabolism,and metal ion transport were significantly affected under LTC or HT treatment when compared to 0℃.Our analyses provide insights into transcriptome responses to postharvest treatments in loquat fruit.

Ethylene†and fruit softening

This review is concerned with the mechanisms controlling fruit softening.Master genetic regulators switch on the ripening programme and the regulatory pathway branches downstream,with separate controls for distinct quality attributes such as colour,flavour,texture,and aroma.Ethylene plays a critical role as a ripening hormone and is implicated in controlling different facets of ripening,including texture change,acting through a range of transcriptional regulators,and this signalling can be blocked using 1-methylcyclopropene.A battery of at least seven cell-wall-modifying enzymes,most of which are synthesized de novo during ripening,cause major alterations in the structure and composition of the cell wall components and contribute to the softening process.Significant differences between fruits may be related to the precise structure and composition of their cell walls and the enzymes recruited to the ripening programme during evolution.Attempts to slow texture change and reduce fruit spoilage by delaying the entire ripening process can often affect negatively other aspects of quality,and low temperatures,in particular,can have deleterious effects on texture change.Gene silencing has been used to probe the function of individual genes involved in different aspects of ripening,including colour,flavour,ethylene synthesis,and particularly texture change.The picture that emerges is that softening is a multi-genic trait,with some genes making a more important contribution than others.In future,it may be possible to control texture genetically to produce fruits more suitable for our needs.