Basic helix-loop-helix(bHLH)transcription factor MdbHLH3 negatively affects the storage performance of postharvest apple fruit

The storage period of fleshy fruits greatly affects their quality and selection,and is largely controlled by genetic factors.Therefore,it is imperative to elucidate how genetic factors affect fruit ripening and its storage.Here,we evaluated the postharvest storage properties of the basic helix-loop-helix(bHLH)transcription factor MdbHLH3-overexpressing transgenic Royal gala apple fruits.During storage,the contents of starch,malic acid,fructose,glucose,and sucrose in fruits of three MdbHLH3 transgenic lines were always higher than those of the wild-type(WT)control.Interestingly,the sugar-acid ratio also showed the same trend during fruit storage.Additionally,the fruit firmness decreased with increasing storage time,and the contents of cell wall components such as water-soluble pectin and cellulose in transgenic fruits were higher than those in control fruits,while the firmness of transgenic fruits was lower than that in WT control fruits.Though the ethylene release rate in both showed the same trend(firstly increasing,then decreasing,and finally peaking)in 90-day stored fruits,transgenic apples had higher ethylene levels than the WT control throughout storage.Furthermore,the activities of membrane peroxidase,antioxidant enzymes,and fruit ripening enzymes in all transgenic fruits were significantly higher than those in the WT control.Thus,our findings show how MdbHLH3 negatively regulates and reduces apple storage time.This may prove useful for not only developing biotechnological strategies,but also support traditional breeding programs,to help improve the storage time of fleshy fruits.

Genome-wide identification and expression analyses of homeodomain-leucine zipper family genes reveal their involvement in stress response in apple(Malus×domestica)

The homeodomain-leucine zipper(HD-Zip)family has been shown to perform amultitude of functions during plant development and stress responses;however,the familymembers and functions have not been identified in apple(Malus×domestica).In this study,83 HD-Zips(MdHDZs)were identified in the apple genome.They were assembled into four subgroups according to the classification in Arabidopsis,where MdHDZs in the same subgroup had similar gene structures and conserved protein motifs.Putative cis-element analysis of MdHDZs promoter regions uncovered numerous elements related to the response of stress and plant hormones.In addition,twelve transcripts of the MdHDZs showed different expression patterns under salt,drought,low temperature and ABA stresses by quantitative reverse transcription-PCR(qRT-PCR)assay.To further explore the function of MdHDZs in apple,MdHDZ3 was selected to verify its function under salt,low temperature and ABA stresses;and genetic transformation was used to obtain MdHDZ3 transgenic apple calli.The results demonstrated that MdHDZ3 increased sensitivity to salt,low temperature and abscisic acid in apple calli,suggesting that MdHDZ3 plays an important role in response to stresses.Subcellular localization and three-dimensional structural analysis revealed that MdHDZ3 was a nuclear-localized protein.Taken together,these findings provide potential information for further identification of HD-Zip proteins in apple.

Guest Editorial:Special Issue on Fruit Quality and Healthy Nutrition

Fleshy fruit is the most important type of horticultural product,playing an irreplaceable role in the improvement of dietary structure,the balance of nutrition,and the intake of physiological active substances such as vitamins in daily life.Fruit quality is the core of the current and future horticultural industry's healthy development and market competitiveness.