A cryptic variation in a member of the Ovate Family Proteins is underlying the melon fruit shape QTL fsqs8.1

Genomic analysis of fruit size and shape traits in apple: unveiling candidate genes through GWAS analysis

Genomic tools facilitate the efficient selection of improved genetic materials within a breeding program. Here, we focus on two apple fruit quality traits: shape and size. We utilized data from 11 fruit morphology parameters gathered across three years of harvest from 355 genotypes of the apple REFPOP collection, which serves as a representative sample of the genetic variability present in European-cultivated apples. The data were then employed for genome-wide association studies (GWAS) using the FarmCPU and the BLINK models. The analysis identified 59 SNPs associated with fruit size and shape traits (35 with FarmCPU and 45 with BLINK) responsible for 71 QTNs. These QTNs were distributed across all chromosomes except for chromosomes 10 and 15. Thirty-four QTNs, identified by 27 SNPs, were related for size traits, and 37 QTNs, identified by 26 SNPs, were related to shape attributes. The definition of the haploblocks containing the most relevant SNPs served to propose candidate genes, among them the genes of the ovate family protein MdOFP17 and MdOFP4 that were in a 9.7kb haploblock on Chromosome 11. RNA-seq data revealed low or null expression of these genes in the oblong cultivar "Skovfoged" and higher expression in the flat "Grand'mere." The Gene Ontology enrichment analysis support a role of OFPs and hormones in shape regulation. In conclusion, this comprehensive GWAS analysis of the apple REFPOP collection has revealed promising genetic markers and candidate genes associated with apple fruit shape and size attributes, providing valuable insights that could enhance the efficiency of future breeding programs.

Form and contour: breeding and genetics of organ shape from wild relatives to modern vegetable crops

Shape is a primary determinant of consumer preference for many horticultural crops and it is also associated with many aspects of marketing, harvest mechanics, and postharvest handling. Perceptions of quality and preference often map to specific shapes of fruits, tubers, leaves, flowers, roots, and other plant organs. As a result, humans have greatly expanded the palette of shapes available for horticultural crops, in many cases creating a series of market classes where particular shapes predominate. Crop wild relatives possess organs shaped by natural selection, while domesticated species possess organs shaped by human desires. Selection for visually-pleasing shapes in vegetable crops resulted from a number of opportunistic factors, including modification of supernumerary cambia, allelic variation at loci that control fundamental processes such as cell division, cell elongation, transposon-mediated variation, and partitioning of photosynthate. Genes that control cell division patterning may be universal shape regulators in horticultural crops, influencing the form of fruits, tubers, and grains in disparate species. Crop wild relatives are often considered less relevant for modern breeding efforts when it comes to characteristics such as shape, however this view may be unnecessarily limiting. Useful allelic variation in wild species may not have been examined or exploited with respect to shape modifications, and newly emergent information on key genes and proteins may provide additional opportunities to regulate the form and contour of vegetable crops.

A Novel Introgression Line Library Derived from a Wild Melon Gives Insights into the Genetics of Melon Domestication, Uncovering New Genetic Variability Useful for Breeding

A collection of 30 melon introgression lines (ILs) was developed from the wild accession Ames 24297 (TRI) into 'Piel de Sapo' (PS) genetic background. Each IL carried an average of 1.4 introgressions from TRI, and the introgressions represented 91.4% of the TRI genome. Twenty-two ILs, representing 75% of the TRI genome, were evaluated in greenhouse (Algarrobo and Meliana) and field (Alcàsser) trials, mainly to study traits related to domestication syndrome such as fruit weight (FW) and flesh content (FFP), as well as other fruit quality traits as fruit shape (FS), flesh firmness (FF), soluble solid concentration (SSC), rind color and abscission layer. The IL collection showed an impressive variation in size-related traits, with FW ranging from 800 to 4100 g, reflecting the strong effect of the wild genome on these traits. Most of the ILs produced smaller fruits compared with PS; however, unexpectedly, the IL TRI05-2 produced bigger fruits, likely due to new epistatic interacions with the PS genetic background. In contrast, the genotypic effect for FS was smaller, and few QTLs with notable effects were detected. Interestingly, variability was also observed for FFP, FF and SSC, rind color and abscission layer formation. Genes in these introgressions are candidates for having been involved in melon domestication and diversification as well. These results confirm that the TRI IL collection is a very powerful tool for mapping traits of agronomic interest in melon, allowing the confirmation of previously reported QTLs and the identification of new ones to better understand the domestication process of this crop.

Pan-genome and multi-parental framework for high-resolution trait dissection in melon (Cucumis melo)

Linking genotype with phenotype is a fundamental goal in biology and requires robust data for both. Recent advances in plant-genome sequencing have expedited comparisons among multiple-related individuals. The abundance of structural genomic within-species variation that has been discovered indicates that a single reference genome cannot represent the complete sequence diversity of a species, leading to the expansion of the pan-genome concept. For high-resolution forward genetics, this unprecedented access to genomic variation should be paralleled and integrated with phenotypic characterization of genetic diversity. We developed a multi-parental framework for trait dissection in melon (Cucumis melo), leveraging a novel pan-genome constructed for this highly variable cucurbit crop. A core subset of 25 diverse founders (MelonCore25), consisting of 24 accessions from the two widely cultivated subspecies of C. melo, encompassing 12 horticultural groups, and 1 feral accession was sequenced using a combination of short- and long-read technologies, and their genomes were assembled de novo. The construction of this melon pan-genome exposed substantial variation in genome size and structure, including detection of ~300 000 structural variants and ~9 million SNPs. A half-diallel derived set of 300 F₂ populations, representing all possible MelonCore25 parental combinations, was constructed as a framework for trait dissection through integration with the pan-genome. We demonstrate the potential of this unified framework for genetic analysis of various melon traits, including rind color intensity and pattern, fruit sugar content, and resistance to fungal diseases. We anticipate that utilization of this integrated resource will enhance genetic dissection of important traits and accelerate melon breeding.

Fruit Morphology and Ripening-Related QTLs in a Newly Developed Introgression Line Collection of the Elite Varieties 'Védrantais' and 'Piel de Sapo'

Melon is an economically important crop with widely diverse fruit morphology and ripening characteristics. Its diploid sequenced genome and multiple genomic tools make this species suitable to study the genetic architecture of fruit traits. With the development of this introgression line population of the elite varieties 'Piel de Sapo' and 'Védrantais', we present a powerful tool to study fruit morphology and ripening traits that can also facilitate characterization or pyramidation of QTLs in inodorous melon types. The population consists of 36 lines covering almost 98% of the melon genome, with an average of three introgressions per chromosome and segregating for multiple fruit traits: morphology, ripening and quality. High variability in fruit morphology was found within the population, with 24 QTLs affecting six different traits, confirming previously reported QTLs and two newly detected QTLs, FLQW5.1 and FWQW7.1. We detected 20 QTLs affecting fruit ripening traits, six of them reported for the first time, two affecting the timing of yellowing of the rind (EYELLQW1.1 and EYELLQW8.1) and four at the end of chromosome 8 affecting aroma, abscission and harvest date (EAROQW8.3, EALFQW8.3, ABSQW8.3 and HARQW8.3). We also confirmed the location of several QTLs, such as fruit-quality-related QTLs affecting rind and flesh appearance and flesh firmness.

Genome-wide analysis of OFP gene family in pepper (Capsicum annuum L.)

Ovate family proteins (OFPs) are transcriptional inhibitors that regulate plant growth and development and play important roles in the synthesis of secondary cell walls during pollen development. This study identified the pepper OFP gene family based on the genome-wide analysis and used bioinformatics methods to provide a fundamental profile of the gene family. 74 OFP genes with typical Ovate domain were identified in cultivated pepper Zunla-1, wild pepper Chiltepin and CM334. Chromosome mapping revealed that CazOFP genes were unevenly distributed on 11 chromosomes and Chr00 in Zunla-1, CacOFP genes on 12 chromosomes in Chiltepin, and CamOFP genes on 12 chromosomes and two Scaffflods in CM334. Gene structure analysis revealed that CaOFP genes possessed 1-3 exons, and the analysis of physicochemical properties suggested that CaOFPs were hydrophilic. Many cis-acting elements were identified in the promoter region of CaOFP genes, including ABRE, ARE, Box 4, G-box, TC-rich, and TCT-motif. The expression patterns of pepper at different growth stages showed that CaOFP genes were actively involved in the growth and fruit development of pepper, and CazOFP16 and CazOFP17 were actively involved in response to multiple hormones and stress events. qRT-PCR was also used to verify the expression of CazOFP gene in two developmental stages of seven pepper varieties with different fruit shapes, and it was found that CaOFP genes may be involved in the formation of fruit type in pepper. This study provides theoretical and practical evidence for future research on the OFP gene family.

Mining Candidate Genes Related to Heavy Metals in Mature Melon (Cucumis melo L.) Peel and Pulp Using WGCNA

The content of metal ions in fruits is inseparable from plant intake of trace elements and health effects in the human body. To understand metal ion content in the fruit and pericarp of melon (Cucumis melo L.) and the candidate genes responsible for controlling this process, we analyzed the metal ion content in distinct parts of melon fruit and pericarp and performed RNA-seq. The results showed that the content of metal ions in melon fruit tissue was significantly higher than that in the pericarp. Based on transcriptome expression profiling, we found that the fruit and pericarp contained elevated levels of DEGs. GO functional annotations included cell surface receptor signaling, signal transduction, organic substance metabolism, carbohydrate derivative binding, and hormone-mediated signaling pathways. KEGG pathways included pectate lyase, pentose and glucuronate interconversions, H⁺-transporting ATPase, oxidative phosphorylation, plant hormone signal transduction, and MAPK signaling pathways. We also analyzed the expression patterns of genes and transcription factors involved in hormone biosynthesis and signal transduction. Using weighted gene co-expression network analysis (WGCNA), a co-expression network was constructed to identify a specific module that was significantly correlated with the content of metal ions in melon, after which the gene expression in the module was measured. Connectivity and qRT–PCR identified five candidate melon genes, LOC103501427, LOC103501539, LOC103503694, LOC103504124, and LOC107990281, associated with metal ion content. This study provides a theoretical basis for further understanding the molecular mechanism of heavy metal ion content in melon fruit and peel and provides new genetic resources for the study of heavy metal ion content in plant tissues.

Ethylene plays a dual role in sex determination and fruit shape in cucurbits

Shapes of vegetables and fruits are the result of adaptive evolution and human selection. Modules controlling organ shape have been identified. However, little is known about signals coordinating organ development and shape. Here, we describe the characterization of a melon mutation rf1, leading to round fruit. Histological analysis of rf1 flower and fruits revealed fruit shape is determined at flower stage 8, after sex determination and before flower fertilization. Using positional cloning, we identified the causal gene as the monoecy sex determination gene CmACS7, and survey of melon germplasms showed strong association between fruit shape and sexual types. We show that CmACS7-mediated ethylene production in carpel primordia enhances cell expansion and represses cell division, leading to elongated fruit. Cell size is known to rise as a result of endoreduplication. At stage 8 and anthesis, we found no variation in ploidy levels between female and hermaphrodite flowers, ruling out endoreduplication as a factor in fruit shape determination. To pinpoint the gene networks controlling elongated versus round fruit phenotype, we analyzed the transcriptomes of laser capture microdissected carpels of wild-type and rf1 mutant. These high-resolution spatiotemporal gene expression dynamics revealed the implication of two regulatory modules. The first module implicates E2F-DP transcription factors, controlling cell elongation versus cell division. The second module implicates OVATE- and TRM5-related proteins, controlling cell division patterns. Our finding highlights the dual role of ethylene in the inhibition of the stamina development and the elongation of ovary and fruit in cucurbits.