Explore the vast range of titles available.

Powdery mildew is a major fungal disease on squash and pumpkin (Cucurbita spp.) in the US and throughout the world. Genetic resistance to the disease is not known to occur naturally within Cucurbita pepo and only infrequently in Cucurbita moschata, but has been achieved in both species through the introgression of a major resistance gene from the wild species Cucurbita okeechobeensis subsp. martinezii. At present, this gene, Pm-0, is used extensively in breeding, and is found in nearly all powdery mildew-resistant C. pepo and C. moschata commercial cultivars. In this study, we mapped C. okeechobeensis subsp. martinezii-derived single nucleotide polymorphism (SNP) alleles in a set of taxonomically and morphologically diverse and resistant C. pepo and C. moschata cultivars bred at Cornell University that, by common possession of Pm-0, form a shared-trait introgression panel. High marker density was achieved using genotyping-by-sequencing, which yielded over 50,000 de novo SNP markers in each of the three Cucurbita species genotyped. A single 516.4 kb wild-derived introgression was present in all of the resistant cultivars and absent in a diverse set of heirlooms that predated the Pm-0 introgression. The contribution of this interval to powdery mildew resistance was confirmed by association mapping in a C. pepo cultivar panel that included the Cornell lines, heirlooms, and 68 additional C. pepo cultivars and with an independent F2 population derived from C. okeechobeensis subsp. martinezii x C. moschata. The interval was refined to a final candidate interval of 76.4 kb and CAPS markers were developed inside this interval to facilitate marker-assisted selection.

Background Pumpkins ( Cucurbita moschata ; Cucurbitaceae) are valued for their fruits and seeds and are rich in nutrients. Carotenoids and sugar contents, as main feature of pumpkin pulp, are used to determine the fruit quality. Results Two pumpkin germplasms, CMO-X and CMO-E, were analyzed regarding the essential quality traits such as dry weight, soluble solids, organic acids, carotenoids and sugar contents. For the comparison of fruit development in these two germplasms, fruit transcriptome was analyzed at 5 different developmental stages from 0 d to 40 d in a time course manner. Putative pathways for carotenoids biosynthesis and sucrose metabolism were developed in C. moschata fruit and homologs were identified for each key gene involved in the pathways. Gene expression data was found consistent with the accumulation of metabolites across developmental stages and also between two germplasms. PSY , PDS , ZEP , CRTISO and SUS , SPS , HK , FK were found highly correlated with the accumulation of carotenoids and sucrose metabolites, respectively, at different growth stages of C. moschata as shown by whole transcriptomic analysis. The results of qRT-PCR analysis further confirmed the association of these genes. Conclusion Developmental regulation of the genes associated with the metabolite accumulation can be considered as an important factor for the determination of C. moschata fruit quality. This research will facilitate the investigation of metabolic profiles in other cultivars.

Background The core regulation of the abscisic acid (ABA) signalling pathway comprises the multigenic families PYL , PP2C, and SnRK2 . In this work, we conducted a genome-wide study of the components of these families in Cucurbita pepo . Results The bioinformatic analysis of the C. pepo genome resulted in the identification of 19 CpPYL , 102 CpPP2C and 10 CpSnRK2 genes. The investigation of gene structure and protein motifs allowed to define 4 PYL, 13 PP2C and 3 SnRK2 subfamilies. RNA-seq analysis was used to determine the expression of these gene families in different plant organs, as well as to detect their differential gene expression during germination, and in response to ABA and cold stress in leaves. The specific tissue expression of some gene members indicated the relevant role of some ABA signalling genes in plant development. Moreover, their differential expression under ABA treatment or cold stress revealed those ABA signalling genes that responded to ABA, and those that were up- or down-regulated in response to cold stress. A reduced number of genes responded to both treatments. Specific PYL - PP2C - SnRK2 genes that had potential roles in germination were also detected, including those regulated early during the imbibition phase, those regulated later during the embryo extension and radicle emergence phase, and those induced or repressed during the whole germination process. Conclusions The outcomes of this research open new research lines for agriculture and for assessing gene function in future studies.

High-throughput screening of an ethyl methanesulfonate-generated mutant collection of Cucurbita pepo using the ethylene triple-response test resulted in the identification of two semi-dominant ethylene-insensitive mutants: etr1a and etr2b. Both mutations altered sex determination mechanisms, promoting conversion of female into bisexual or hermaphrodite flowers, and monoecy into andromonoecy, thereby delaying the transition to female flowering and reducing the number of pistillate flowers per plant. The mutations also altered the growth rate and maturity of petals and carpels in pistillate flowers, lengthening the time required for flowers to reach anthesis, as well as stimulating the growth rate of ovaries and the parthenocarpic development of fruits. Whole-genome sequencing allowed identification of the causal mutation of the phenotypes as two missense mutations in the coding region of CpETR1A and CpETR2B, each one corresponding to one of the duplicates of ethylene receptor genes highly homologous to Arabidopsis ETR1 and ETR2. The phenotypes of homozygous and heterozygous single- and double-mutant plants indicated that the two ethylene receptors cooperate in the control of the ethylene response. The level of ethylene insensitivity, which was determined by the strength of each mutant allele and the dose of wild-type and mutant etr1a and etr2b alleles, correlated with the degree of phenotypic changes in the mutants.

The mitochondrial genomes of seed plants are unusually large and vary in size by at least an order of magnitude. Much of this variation occurs within a single family, the Cucurbitaceae, whose genomes range from an estimated 390 to 2,900 kb in size. We sequenced the mitochondrial genomes of Citrullus lanatus (watermelon: 379,236 nt) and Cucurbita pepo (zucchini: 982,833 nt)—the two smallest characterized cucurbit mitochondrial genomes—and determined their RNA editing content. The relatively compact Citrullus mitochondrial genome actually contains more and longer genes and introns, longer segmental duplications, and more discernibly nuclear-derived DNA. The large size of the Cucurbita mitochondrial genome reflects the accumulation of unprecedented amounts of both chloroplast sequences (>113 kb) and short repeated sequences (>370 kb). A low mutation rate has been hypothesized to underlie increases in both genome size and RNA editing frequency in plant mitochondria. However, despite its much larger genome, Cucurbita has a significantly higher synonymous substitution rate (and presumably mutation rate) than Citrullus but comparable levels of RNA editing. The evolution of mutation rate, genome size, and RNA editing are apparently decoupled in Cucurbitaceae, reflecting either simple stochastic variation or governance by different factors.

Background Curcubita ficifolia Bouché (Cucurbitaceae) has high value as a food crop and medicinal plant, and also has horticultural value as rootstock for other melon species. China is home to many different cultivars, but the genetic diversity of these resources and the evolutionary relationships among them, as well as the differences between C. ficifolia and other Cucurbita species, remain unclear. Results We investigated the chloroplast (cp) genomes of 160 C. ficifolia individuals from 31 populations in Yunnan, a major C. ficifolia production area in China. We found that the cp genome of C. ficifolia is ~151 kb and contains 128 genes, of which 86 are protein coding genes, 34 encode tRNA, and eight encode rRNAs. We also identified 64 SSRs, mainly AT repeats. The cp genome was found to contain a total of 204 SNP and 57 indels, and a total of 21 haplotypes were found in the 160 study individuals. The reverse repeat (IR) region of C. ficifolia contained a few differences compared with this region in the six other Cucurbita species. Sequence difference analysis demonstrated that most of the variable regions were concentrated in the single copy (SC) region. Moreover, the sequences of the coding regions were found to be more similar among species than those of the non-coding regions. The phylogenies reconstructed from the cp genomes of 61 representative species of Cucurbitaceae reflected the currently accepted classification, in which C. ficifolia is sister to the other Cucurbita species, however, different interspecific relationships were found between Cucurbita species. Conclusions These results will be valuable in the classification of C. ficifolia genetic resources and will contribute to our understanding of evolutionary relationships within the genus Cucurbita .

Phytophthora capsici Leonian, the causal agent of foliar blight, root rot, fruit rot and crown rot syndromes in squash ( Cucurbita moschata ), is a devastating pathogen worldwide. Resistance to Phytophthora crown rot in University of Florida breeding line #394-1-27-12 ( C. moschata ) is conferred by three independent dominant genes (R1R2R3). Availability of DNA markers linked to R1R2R3 genes would allow efficient breeding for Phytophthora crown rot resistance through marker-assisted selection (MAS). The goal of the current study was to identify quantitative trait loci (QTLs) associated with resistance to Phytophthora crown rot in an F 2 population (n = 168) derived from a cross between #394-1-27-12 (R) and Butter Bush (S) using QTL-seq bulk segregant analysis. Whole-genome resequencing of the resistant (n = 20) and susceptible (n = 20) bulk segregants revealed ~ 900,000 single nucleotide polymorphisms distributed across C. moschata genome. Three QTLs significantly (P < 0.05) associated with resistance to Phytophthora crown rot were detected on chromosome 4 ( QtlPC-C04 ), 11 ( QtlPC-C11 ) and 14 ( QtlPC-C14 ). Several markers linked to these QTLs are potential targets for MAS against Phytophthora crown rot in C. moschata . The present study reports the first QTLs associated with Phytophthora crown rot resistance in C. moschata .

The genusCucurbita(squashes, pumpkins, gourds) contains numerous domesticated lineages with ancient New World origins. It was broadly distributed in the past but has declined to the point that several of the crops’ progenitor species are scarce or unknown in the wild. We hypothesize that Holocene ecological shifts and megafaunal extinctions severely impacted wildCucurbita,whereas their domestic counterparts adapted to changing conditions via symbiosis with human cultivators. First, we used high-throughput sequencing to analyze complete plastid genomes of 91 totalCucurbitasamples, comprising ancient (n= 19), modern wild (n= 30), andmodern domestic (n= 42) taxa. This analysis demonstrates independent domestication in eastern North America, evidence of a previously unknown pathway to domestication in northeastern Mexico, and broad archaeological distributions of taxa currently unknown in the wild. Further, sequence similarity between distant wild populations suggests recent fragmentation. Collectively, these results point to wild-type declines coinciding with widespread domestication. Second, we hypothesize that the disappearance of large herbivores struck a critical ecological blow against wildCucurbita,and we take initial steps to consider this hypothesis through crossmammal analyses of bitter taste receptor gene repertoires. Directly, megafauna consumedCucurbitafruits and dispersed their seeds; wildCucurbitawere likely left without mutualistic dispersal partners in the Holocene because they are unpalatable to smaller surviving mammals with more bitter taste receptor genes. Indirectly, megafauna maintained mosaic-like landscapes ideal forCucurbita,and vegetative changes following the megafaunal extinctions likely crowded out their disturbed-ground niche. Thus, anthropogenic landscapes provided favorable growth habitats and willing dispersal partners in the wake of ecological upheaval.

Key message A large fragment deletion of CpAPRR2 , encoding a two-component response regulator-like protein, which influences immature white rind color formation in zucchini ( Cucurbita pepo ). Fruit rind color is an important agronomic trait that affects commodity quality and consumer choice in zucchini ( Cucurbita pepo ). However, the molecular mechanism controlling rind color is unclear. We characterized two zucchini inbred lines: ‘19’ (dark green rind) and ‘113’ (white rind). Genetic analysis revealed white immature fruit rind color to be controlled by a dominant locus ( CpW ). Combining bulked segregant analysis sequencing (BSA-seq) and Kompetitive Allele-Specific PCR (KASP) markers, we mapped the CpW locus to a 100.4 kb region on chromosome 5 and then narrow down the candidate region to 37.5 kb using linkage analysis of 532 BC 1 and 1613 F 2 individuals, including 6 coding genes. Among them, Cp4.1LG05g02070 ( CpAPRR2 ), encoding a two-component response regulator-like protein, was regarded to be a promising candidate gene. The expression level of CpAPRR2 in dark green rind was significantly higher than that in white rind and was induced by light. A deletion of 2227 bp at the 5′ end of CpAPRR2 in ‘113’ might explain the white phenotype. Further analysis of allelic diversity in zucchini germplasm resources revealed rind color to be associated with the deletion of CpAPRR2 . Subcellular localization analysis indicated that CpAPRR2 was a nuclear protein. Transcriptome analysis using near-isogenic lines with dark green (DG) and white (W) rind indicated that genes involved in photosynthesis and porphyrin metabolism pathways were enriched in DG compared with W. Additionally, chlorophyll synthesis-related genes were upregulated in DG. These results identify mechanisms of zucchini rind color and provide genetic resources for breeding.

Key message We identified a 580 bp deletion of CmaKNAT6 coding region influences peel colour of mature Cucurbita maxima fruit. Peel colour is an important agronomic characteristic affecting commodity quality in Cucurbit plants. Genetic mapping of fruit peel colour promotes molecular breeding and provides an important basis for understanding the regulatory mechanism in Cucurbit plants. In the present study, the Cucurbita maxima inbred line ‘9-6’ which has a grey peel colour and ‘U3-3-44’ which has a dark green peel colour in the mature fruit stage, were used as plant materials. At 5–40 days after pollination (DAP), the contents of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids in the ‘U3-3-44’ peels were significantly greater than those in the ‘9-6’ peels. In the epicarp of the ‘9-6’ mature fruit, the presence of nonpigmented cell layers and few chloroplasts in each cell in the pigmented layers were observed. Six generations derived by crossing ‘9-6’ and ‘U3-3-44’ were constructed, and the dark green peel was found to be controlled by a single dominant locus, which was named CmaMg ( mature green peel ). Through bulked-segregant analysis sequencing (BSA-seq) and insertion-deletion (InDel) markers, CmaMg was mapped to a region of approximately 449.51 kb on chromosome 11 using 177 F 2 individuals. Additionally, 1703 F 2 plants were used for fine mapping to compress the candidate interval to a region of 32.34 kb. Five coding genes were in this region, and CmaCh11G000900 was identified as a promising candidate gene according to the reported function, sequence alignment, and expression analyses. CmaCh11G000900 ( CmaKNAT6 ) encodes the homeobox protein knotted-1-like 6 and contains 4 conserved domains. CmaKNAT6 of ‘9-6’ had a 580 bp deletion, leading to premature transcriptional termination. The expression of CmaKNAT6 tended to increase sharply during the early fruit development stage but decrease gradually during the late period of fruit development. Allelic diversity analysis of pumpkin germplasm resources indicated that the 580 bp deletion in the of CmaKNAT6 coding region was associated with peel colour. Subcellular localization analysis indicated that CmaKNAT6 is a nuclear protein. Transcriptomic analysis of the inbred lines ‘9-6’ and ‘U3-3-44’ indicated that genes involved in chlorophyll biosynthesis were more enriched in ‘U3-3-44’ than in ‘9-6’. Additionally, the expression of transcription factor genes that positively regulate chlorophyll synthesis and light signal transduction pathways was upregulated in ‘U3-3-44’. These results lay a foundation for further studies on the genetic mechanism underlying peel colour and for optimizing peel colour-based breeding strategies for C. maxima .