The IAA-and ABA-responsive transcription factor CgMYB58 upregulates lignin biosynthesis and triggers juice sac granulation in pummelo

In citrus,lignin overaccumulation in the juice sac results in granulation and an unpleasant fruit texture and taste.By integrating metabolic phenotyping and transcriptomic analyses,we found 702 differentially expressed genes(DEGs),including 24 transcription factors(TFs),to be significantly correlated with lignin content.CgMYB58 was further identified as a critical R2R3 MYB TF involved in lignin overaccumulation owing to its high transcript levels in Huanong Red-fleshed pummelo(HR,Citrus grandis)fruits.Transient expression of CgMYB58 led to an increase in the lignin content in the pummelo fruit mesocarp,whereas its stable overexpression significantly promoted lignin accumulation and upregulated 19 lignin biosynthetic genes.Among these genes,CgPAL1,CgPAL2,Cg4CL1,and CgC3H were directly modulated by CgMYB58 through interaction with their promoter regions.Moreover,we showed that juice sac granulation in pummelo fruits could be affected by indole-3-acetic acid(IAA)and abscisic acid(ABA)treatments.In HR pummelo,ABA significantly accelerated this granulation,whereas IAA effectively inhibited this process.Taken together,these results provide novel insight into the lignin accumulation mechanism in citrus fruits.We also revealed the theoretical basis via exogenous IAA application,which repressed the expression of CgMYB58 and its target genes,thus alleviating juice sac granulation in orchards.

PpERF3 positively regulates ABA biosynthesis by activating PpNCED2/3 transcription during fruit ripening in peach

The plant hormone ethylene regulates ripening in climacteric fruits.The phytohormone abscisic acid(ABA)affects ethylene biosynthesis,but whether ethylene influences ABA biosynthesis is unknown.To explore this possibility,we investigated the interactions between the ABA biosynthesis genes PpNCED2/3 and the ethylene response transcription factor PpERF3 in peach fruit.The ABA content increased during fruit maturation and reached a peak at stage S4 III.The increase was greatly inhibited by the ethylene inhibitor 1-MCP,which also suppressed PpERF3 expression.PpERF3 shared a similar expression profile with PpNCED2/3,encoding a rate-limiting enzyme involved in ABA biosynthesis,during fruit ripening.A yeast one-hybrid assay suggested that the nuclear-localized PpERF3 might bind to the promoters of PpNCED2/3.PpERF3 increased the expression of PpNCED2/3 as shown by dual-luciferase reporters,promoter-GUS assays and transient expression analyses in peach fruit.Collectively,these results suggest that ethylene promotes ABA biosynthesis through PpERF3’s regulation of the expression of ABA biosynthesis genes PpNCED2/3.

The MADS-box gene FveSEP3 plays essential roles in flower organogenesis and fruit development in woodland strawberry

Flower and fruit development are two key steps for plant reproduction.The ABCE model for flower development has been well established in model plant species;however,the functions of ABCE genes in fruit crops are less understood.In this work,we identi fied an EMS mutant named R27 in woodland strawberry(Fragaria vesca),showing the conversion of petals,stamens,and carpels to sepaloid organs in a semidominant inheritance fashion.Mapping by sequencing revealed that the class E gene homolog FveSEP3(FvH4_4g23530)possessed the causative mutation in R27 due to a G to E amino acid change in the conserved MADS domain.Additional fvesep3^(CR) mutants generated by CRISPR/Cas9 displayed similar phenotypes to fvesep3-R27.Overexpressing wild-type or mutated FveSEP3 in Arabidopsis suggested that the mutation in R27 might cause a dominant-negative effect.Further analyses indicated that FveSEP3 physically interacted with each of the ABCE proteins in strawberry.Moreover,both R27 and fvesep3^(CR) mutants exhibited parthenocarpic fruit growth and delayed fruit ripening.Transcriptome analysis revealed that both common and specific differentially expressed genes were identi fied in young fruit at 6-7 days post anthesis(DPA)of fvesep3 and pollinated wild type when compared to unpollinated wild type,especially those in the auxin pathway,a key hormone regulating fruit set in strawberry.Together,we provided compelling evidence that FveSEP3 plays predominant E functions compared to other E gene homologs in flower development and that FveSEP3 represses fruit growth in the absence of pollination and promotes fruit ripening in strawberry.

The NAM/ATAF1/2/CUC2 transcription factor PpNAC.A59 enhances PpERF.A16 expression to promote ethylene biosynthesis during peach fruit ripening

Peach is a typical climacteric fruit that releases ethylene during fruit ripening.Several studies have been conducted on the transcriptional regulation of ethylene biosynthesis in peach fruit.Herein,an ethylene response factor,PpERF.A16,which was induced by exogenous ethylene,could enhance ethylene biosynthesis by directly inducing the expression of 1-aminocyclopropane-1-carboxylic acid synthase(PpACS1)and 1-aminocyclopropane-1-carboxylic acid oxidase(PpACO1)genes.Moreover,the NAM/ATAF1/2/CUC2(NAC)transcription factor(TF)PpNAC.A59 was coexpressed with PpERF.A16 in all tested peach cultivars.Interestingly,PpNAC.A59 can directly interact with the promoter of PpERF.A16 to induce its expression but not enhance LUC activity driven by any promoter of PpACS1 or PpACO1.Thus,PpNAC.A59 can indirectly mediate ethylene biosynthesis via the NAC-ERF signaling cascade to induce the expression of both PpACS1 and PpACO1.These results enrich the genetic network of fruit ripening in peach and provide new insight into the ripening mechanism of other perennial fruits.

Multiomics analyses unveil the involvement of microRNAs in pear fruit senescence under high-or low-temperature conditions

Senescence leads to declines in fruit quality and shortening of shelf life.It is known that low temperatures(LTs)efficiently delay fruit senescence and that high temperatures(HTs)accelerate senescence.However,the molecular mechanism by which temperature affects senescence is unclear.Herein,through multiomics analyses of fruits subjected to postharvest HT,LT,and room temperature treatments,a total of 56 metabolic compounds and 700 mRNAs were identified to be associated with fruit senescence under HT or LT conditions.These compounds could be divided into antisenescent(I→III)and prosenescent(IV→VI)types.HT affected the expression of 202 mRNAs to enhance the biosynthesis of prosenescent compounds of types V and VI and to inhibit the accumulation of antisenescent compounds of types II and III.LT affected the expression of 530 mRNAs to promote the accumulation of antisenescent compounds of types I and II and to impede the biosynthesis of prosenescent compounds of types IV and V.Moreover,16 microRNAs were isolated in response to HT or LT conditions and interacted with the mRNAs associated with fruit senescence under HT or LT conditions.Transient transformation of pear fruit showed that one of these microRNAs,Novel_188,can mediate fruit senescence by interacting with its target Pbr027651.1.Thus,both HT and LT conditions can affect fruit senescence by affecting microRNA–mRNA interactions,but the molecular networks are different in pear fruit.

Coreless apples generated by the suppression of carpel genes and hormone-induced fruit set

Seedless fruits have high consumer appeal and have made seeded varieties obsolete in some crops.In seedless apple varieties,core tissues which normally contain the seed can be unpalatable,reducing the seedless appeal.Apples are accessory fruit with edible flesh derived from hypanthial tissue–a floral tube fused to a compound ovary.Here we show that through suppression of AGAMOUS-like carpel identity genes and hormone induced fruit set,it is possible to generate coreless and therefore seedless apples.Suppression of AGAMOUS-like genes increased petal whorls and fully eliminated carpel development.Treatments with a combination of gibberellin,cytokinin and auxin,rather than single treatments,were required for fruit initiation in these lines.Transcriptomic analysis of agamous RNAi lines suggested conservation of AGAMOUS-dependent gene networks between apple and Arabidopsis.In the absence of all sexual tissues,the developing fruit continues to grow and follow a ripening process similar to that of a regular apple.The coreless phenotype offers a new concept for pipfruit consumers improving convenience and reducing food waste.

Unraveling a genetic roadmap for improved taste in the domesticated apple

Although taste is an important aspect of fruit quality, an understanding of its genetic control remains elusive in apple and other fruit crops. In this study, we conducted genomic sequence analysis of 497 Malus accessions and revealed erosion of genetic diversity caused by apple breeding and possible independent domestication events of dessert and cider apples. Signatures of selection for fruit acidity and size, but not for fruit sugar content, were detected during the processes of both domestication and improvement. Furthermore, we found that single mutations in major genes affecting fruit taste, including Ma1, MdTDT, and MdSOT2, dramatically decrease malate, citrate, and sorbitol accumulation, respectively, and correspond to important domestication events. Interestingly, Ma1 was identified to have pleiotropic effects on both organic acid content and sugar:acid ratio, suggesting that it plays a vital role in determining fruit taste. Fruit taste is unlikely to have been negatively affected by linkage drag associated with selection for larger fruit that resulted from the pyramiding of multiple genes with minor effects on fruit size. Collectively, our study provides new insights into the genetic basis of fruit quality and its evolutionary roadmap during apple domestication, pinpointing several candidate genes for genetic manipulation of fruit taste in apple.