The abscisic acid-responsive transcriptional regulatory module CsERF110-CsERF53 orchestrates citrus fruit coloration

Carotenoid biosynthesis is closely associated with abscisic acid(ABA)during the ripening process of non-climacteric fruits,but the regulatory mechanism that links ABA signaling to carotenoid metabolism remains largely unclear.Here,we identified two master regulators of ABA-mediated citrus fruit coloration,CsERF110 and CsERF53,which activate the expression of carotenoid metabolism genes(CsGGPPS,CsPSY,CsPDS,CsCRTISO,CsLCYB2,CsLCYE,CsHYD,CsZEP,and CsNCED2)to facilitate carotenoid accumulation.Further investigations showed that CsERF110 not only activates the expression of CsERF53 by binding to its promoter but also interacts with CsERF53 to form the transcriptional regulatory module CsERF110-CsERF53.We also discovered a positive feedback regulatory loop between the ABA signal and carotenoid metabolism regulated by the transcriptional regulatory module CsERF110-CsERF53.Our results reveal that the CsERF110-CsERF53 module responds to ABA signaling,thereby orchestrating citrus fruit coloration.Considering the importance of carotenoid content for citrus and many other carotenoid-rich crops,the revelation of molecular mechanisms that underlie ABA-mediated carotenoid biosynthesis in plants will facilitate the development of transgenic/gene-editing approaches,further contributing to improving the quality of citrus and other carotenoid-rich crops.

A chromosome-level genome assembly for Chinese plum‘Wushancuili'reveals the molecular basis of its fruit color and susceptibility to rain-cracking

Chinese plum(Prunus salicina Lindl.)originates from China and makes a large contribution to the global production of plums.The P.salicina‘Wushancuili'has a green coloration and high fruit quality and is economically important in eliminating poverty and protecting ecology in the Yangtze River Three Gorges Reservoir.However,rain-induced cracking(rain-cracking,literally skin cracking caused by rain)is a limitation to‘Wushancuili'fruit production and causes severe losses.This study reported a high-quality‘Wushancuili'genome assembly consisting of a 302.17-Mb sequence with eight pseudo-chromosomes and a contig N50 of 23.59 Mb through the combination of Illumina sequencing,Pacific Biosciences HiFiⅢsequencing,and high-throughput chromosome conformation capture technology.A total of 25109 protein-coding genes are predicted and 54.17%of the genome is composed of repetitive sequences.‘Wushancuili'underwent a remarkable orthoselection during evolution.Gene identification revealed that loss-of-function in four core MYB10 genes results in the anthocyanin deficiency and absence of red color,revealing the green coloration due to the residual high chlorophyll in fruit skin.Besides,the occurrence of cracking is assumed to be closely associated with cell wall modification and frequently rain-induced pathogen enrichment through transcriptomic analysis.The loss of MYB10 genes might render fruit more susceptible to pathogen-mediated cracking by weakening the epidermal strength and reactive oxygen species(ROS)scavenging.Our findings provided fundamental knowledge regarding fruit coloration and rain-cracking and will facilitate genetic improvement and cultivation management in Chinese plums.

Insights into flavonoid biosynthesis during cucumber fruit peel coloration based on metabolite profiling and transcriptome analyses

The fruit peel color is a crucial trait of cucumber.To better understand the molecular mechanisms underlying cucumber peel coloration,we compared the UPLC-ESI-MS/MS-based flavonoid metabolomic and RNA sequencing-based transcriptomic profiling of the brown peeled cucumber line‘PW’at six developmental stages.A total of 210 flavonoid metabolites were identified.Of which,117 flavonoid metabolites were differentially accumulated.In this study,weighted gene co-expression network analysis combined with Kyoto Encyclopedia of Gene and Genomes enrichment analysis revealed key genes coding for seven enzymes and eight transcription factors(TFs)associated with flavonoid biosynthesis.Among them,the R2R3MYB CsaV3_4G001130 is the best candidate gene that is responsible for controlling mature fruit colors in cucumber.Sanger sequencing revealed one nonsynonymous SNP in the exon of CsaV3_4G001130 among the selected 11 cucumber lines,which introduced a premature stop codon,generating a truncated protein in pale yellow or creamy peeled fruits.Yeast two-hybrid assays showed a direct interaction of CsaV3_4G001130 with the bHLH TF CsaV3_1G002260 and the WD40 protein CsaV3_5G001800.However,the interactions were influenced by the nonsynonymous SNP we identified.Our finding revealed that the integrated transcriptome and metabolome analysis further demonstrated that the abundance of some pigmented flavonoids(especially anthocyanins and chalcones)contributed to the coloration of‘PW’fruits.These findings pave the way for elucidation of flavonoid biosynthesis and improvement of cucumber peel color in the future.

A novel histone methyltransferase gene Cg SDG40 positively regulates carotenoid biosynthesis during citrus fruit ripening

The flesh color of pummelo(Citrus maxima)fruits is highly diverse and largely depends on the level of carotenoids,which are beneficial to human health.It is vital to investigate the regulatory network of carotenoid biosynthesis to improve the carotenoid content in pummelo.However,the molecular mechanism underlying carotenoid accumulation in pummelo is not fully understood.In this study,we identified a novel histone methyltransferase gene,CgSDG40,involved in carotenoid regulation by analyzing the flesh transcriptome of typical white-fleshed pummelo,red-fleshed pummelo and extreme-colored F1 hybrids from a segregated pummelo population.Expression of CgSDG40 corresponded to flesh color change and was highly coexpressed with CgPSY1.Interestingly,CgSDG40 and CgPSY1 are located physically adjacent to each other on the chromosome in opposite directions,sharing a partially overlapping promoter region.Subcellular localization analysis indicated that CgSDG40 localizes to the nucleus.Overexpression of CgSDG40 significantly increased the total carotenoid content in citrus calli relative to that in wild type.In addition,expression of CgPSY1 was significantly activated in overexpression lines relative to wild type.Taken together,our findings reveal a novel histone methyltransferase regulator,CgSDG40,involved in the regulation of carotenoid biosynthesis in citrus and provide new strategies for molecular design breeding and genetic improvement of fruit color and nutritional quality.

Modeling Study of Fruit Morphological Formation in Melon

Modeling of fruit morphological formation in melon is important for realizing virtual and digital plant growth.The objective of this study was to characterize the changes in patterns of fruit growth characters during plant development.In cultivar experiments,a high-resolution wireless vision sensor network has been developed to realize non-contact automatic uninterrupted measurement of the fruit shape micro-change （fruit size,color,and net）.Results showed that the fruit swelling process （vertical and horizontal diameters） exhibited a slow-rapid-slow pattern,which could be well described with a logistic curve against growing degree days （GDD）;fruit color changes based on the RGB values could be represented by quadratic relationship to cumulative GDD;the fruit net changes over growth progress could be partitioned into three phases according to the time interval.The first phase was from 1 to 30 days after pollination （DAP）,in which the vertical stripe appeared at fruit middle part and the horizontal stripe at fruit petiole and hilum part as well;the second phase was from 30 to 40 DAP,the horizontal stripe occurred at fruit middle part and the net was formed;the third phase was the process started from 40 DAP,the netted breadth and thickness were gradually increased.The model was validated with the independent data from the experiment,and the mean RMSE （root mean square error） of fruit were 0.36 and 0.28 cm for vertical and horizontal diameters,11.9 for fruit color,and 0.45 cm for stripe length and diameter at varied GDD,respectively.This work is beneficial to a reliable foundation for study the relationship between morphological formation and physiological change of the melon fruit internally and then realize the intelligent precision management to improve the yield and quality of greenhouse melon production.

Tissue differential expression of lycopene β-cyclase gene in papaya

Carotene pigments in flowers and fruits are distinct features related to fitness advantages such as attracting insects forpollination and birds for seed dispersal.In papaya,the flesh color of the fruit is considered a quality trait that correlateswith nutritional value and is linked to shelf-life of the fruit.To elucidate the carotenoid biosynthesis pathway in papaya,we took a candidate gene approach to clone the lycopene β-cyclase gene,LCY-B.A papaya LCY-B ortholog,cpLCY-B,was successfully identified from both cDNA and bacterial artificial chromosome(BAC)libraries and complete genomicsequence was obtained from the positive BAC including the promoter region.This cpLCY-B shared 80% amino acididentity with citrus LCY-B.However,full genomic sequences from both yellow- and red-fleshed papaya were identical.Quantitative real-time PCR(qPCR)revealed similar levels of expression at six different maturing stages of fruits forboth yellow-and red-fleshed genotypes.Further expression analyses of cpLCY-B showed that its expression levels wereseven- and three-fold higher in leaves and,respectively,flowers than in fruits,suggesting that cpLCY-B is down-regulatedduring the fruit ripening process.

Inter-specific and intra-specific variability in fruit color preference in two species of Turdus

One of the main hypotheses proposed to explain the evolution of fruit color deals with a preference of avian frugivores for specific colors,mainly black and red,which are the most common fruit colors in many of the studied habitats.I analyzed fruit color preferences by wild birds belonging to 2 species of the highly frugivorous genus Turdus(Eurasian Blackbird Turdus merula Linnaeus,1758 and Redwing Turdus iliacus Linnaeus,1758)by means of captivity experiments with artificial fruits.Despite important within-individual(i.e.temporal)and among-individual variability,consistent patterns of species-specific color preferences emerged.Eurasian Blackbirds tended to prefer red over blue,green and black,whereas Redwings seemed to prefer black over the rest.Green was systematically avoided by both species,suggesting that it might signal unripeness of fruits.Both preferred colors have been previously reported as the most common among fleshy-fruited plants.The high variability,both within and between individuals,in preferences suggests that they can be subject to changes through experience and learning and,therefore,are not likely to drive the evolution of fruit color.The main differences between both species could be related to the most common fruit color they fed upon during the last months before capture.

Genetic diversity and offspring fitness in the red and white fruit color morphs of the wild strawberry Fragaria pentaphylla

Aims Fruit color polymorphisms are widespread in plants,but what maintains them is largely unclear.One hypothesis is that some morphs are preferred by dispersers while others have higher pre-or postdispersal fitness.This leads to the prediction that fruit color morphs will differ in pre-or postdispersal fitness.Methods We compared genetic and clonal diversity,mating system,morphological traits that might be associated with resistance to freezing,and germination,survival and seed production of progeny of the red and white fruit morphs in a population of a diploid,wild strawberry,Fragaria pentaphylla,from south-central China.Important Findings The red morph was much more abundant than the white but did not show higher genetic diversity as measured by observed and effective numbers of alleles,Shannon information index,or expected or observed heterozygosities.AMOVA showed that most of the genetic variation in the population was within rather than between morphs.Morphs did not differ in mating system parameters,and no significant biparental inbreeding was found in either morph.Gene flow between two morphs was high(N_(m)=6.89).Seeds of the red morph germinated about 2 days earlier and had a 40%higher rate of germination than those of the white morph,but survival of seedlings and seed production by surviving offspring did not differ between morphs.The whole postdispersal fitness of the red morph was about two times higher than that of the white morph.Red morphs had hairier petioles but not more surface wax on leaves.Overall,results showed partial evidence for difference in pre-and postdispersal fitness between fruit color morphs in F.pentaphylla.Differences in fitness independent of dispersal may thus partially account for fruit color polymorphism in all cases.

An ACCUMULATION AND REPLICATION OF CHLOROPLASTS 5 gene mutation confers light green peel in cucumber

The peel color of fruit is an important commercial trait in cucumber, but the underlying molecular basis is largely unknown. A mutant showing light green exocarp was discovered from ethyl methane sulfonate （EMS） mutagenized cucumber line 406 with dark green exocarp. Genetic analysis showed the mutant phenotype is conferred by a single recessive gene, here designated as lgp （light green peel）. By re-sequencing of bulked segregants, we identified the candidate gene Csa7Go51430 encoding ACCUMULATION AND REPLICATION OF CHLOROPLASTS 5 （ARCS） that plays a vital role in chloroplast division in Arabidopsis. A single nucleotide polymorphism （SNP） causing amino acid alteration in the conserved GTPase domain of Csa7Go5143o showed co-segregation with the altered phenotype. Furthermore, the transient RNA interference of this gene resulted in reduced number and enlarged size of chloroplasts, which were also observed in the Igp mutant. This evidence supports that the non-synonymous SNP in Csa7G051430 is the causative mutation for the light green peel. This study provides a new allele for cucumber breeding for light green fruits and additional resource for the study of chloroplast development.