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Summary Seedlessness in grapes is one of the features most appreciated by consumers. However, the mechanisms underlying seedlessness in grapes remain obscure. Here, we observe small globular embryos and globular embryos in Pinot Noir and Thompson Seedless from 20 to 30 days after flowering (DAF). From 40 to 50 DAF, we observe torpedo embryos and cotyledon embryos in Pinot Noir but aborted embryos and endosperm in Thompson Seedless. Thus, RNA‐Seq analyses of seeds at these stages from Thompson Seedless and Pinot Noir were performed. A total of 6442 differentially expressed genes were identified. Among these, genes involved in SA biosynthesis, VvEDS1 and VvSARD1, were more highly expressed in Thompson Seedless than in Pinot Noir. Moreover, the content of endogenous SA is at least five times higher in Thompson Seedless than in Pinot Noir. Increased trimethylation of H3K27 of VvEDS1 and VvSARD1 may be correlated with lower SA content in Pinot Noir. We also demonstrate that VvHDZ28 positively regulates the expression of VvEDS1. Moreover, over‐expression of VvHDZ28 results in seedless fruit and increased SA contents in Solanum lycopersicum. Our results reveal the potential role of SA and feedback regulation of VvHDZ28 in seedless grapes.

In plant biotechnology, triploid breeding has become a useful method with substantial benefits for improving agriculture. Triplotypes, having three sets of chromosomes, frequently exhibit superior qualities such as greater resistance to environmental stressors, increased vigor, and seedlessness. This article explores the methods used to produce triploids, such as endosperm culture, somatic cell fusion, hybridization between diploid and tetraploid plants, and colchicine treatment. There are benefits and drawbacks to each technique, contributing to the diversity of triploid plants found in crop and horticultural species. The review also explores a wide range of applications of triploid plants, particularly in enhancing fruit quality, increasing biomass production, and improving stress tolerance. Examples from crops like citrus, bananas, and ornamental plants are highlighted to underscore the commercial and ecological significance of triploids. Additionally, we discuss over ways to detect and validate triploid plants in their early developmental phases by integrating molecular markers like single nucleotide polymorphisms (SNPs), amplified fragment length polymorphisms (AFLP), and simple sequence repeats (SSR). The effectiveness and accuracy of triploid breeding programs are greatly enhanced by these markers. This review also highlights the importance of integrating omics approaches, such as transcriptomics, proteomics, metabolomics, and genomics, in the study and development of triploid plant production which offers deeper insights into the genetic and molecular mechanisms underlying triploidy. In summary, the present study offers perspectives on the potential of triploid breeding in the future, highlighting its significance in sustainable agriculture and crop enhancement tactics. Key message Triploid breeding is a powerful tool for crop improvement because it provides benefits like stress resistance, increased vigor, and seedlessness. This review discusses different triploid production techniques, molecular markers for detection, and omic approaches to comprehend triploidy, emphasizing its function in improved crop traits and sustainable agriculture.

Background Both parthenocarpy and stenospermocarpy lead to seedless grapes. Only parthenocarpy, which is rather rare, generates berries with a complete absence of seed tissues. Stenospermocarpy, which is instead more common, produces berries with seed traces because seed development is promoted by embryo formation and then arrested by its abortion. In viticulture, parthenocarpic varieties account for a minority of the production of seedless table grapes, while they are more commonly used for raisins and very rarely for winemaking. Parthenocarpy is the putative cause of seedlessness in Corinto Nero, a bud sport of the seeded winegrape Sangiovese. In our previous studies, embryo sac abnormalities arising from meiotic disorders were accompanied by transcriptional changes in gene functions linked to gametophyte development and ovule fertilization. Here, with the aim of elucidating the cause of parthenocarpy in Corinto Nero, comparative histological and genomic analyses were performed. Results Histologically, Corinto Nero showed abnormalities in megasporogenesis and the arrest of female gametophyte development very early during the megagametogenesis, compared to seeded Sangiovese. Genetically, Corinto Nero showed putative private mutations in candidate genes with functions related to cell cycle, meiosis and mitosis, compared to ten Sangiovese bud sports, which differed phenotypically from one another and from Corinto Nero for diverse traits, but they all were seeded. One of these mutations was validated in a Disrupted Meiotic cDNA1 homolog gene, which has a missense variant and a significant lower expression at key reproductive developmental stages in Corinto Nero. Conclusions This work provided a list of candidate genes with somatic mutations in Corinto Nero that possibly impair sporogenesis and gametogenesis, preventing seed development. Sangiovese has a genetic predisposition to develop ovary disorders, and to forcibly set fruit in absence of pollination, which may have been turned into full expression of parthenocarpy in Corinto Nero by further mutations. A systematic genome editing of the candidate genes in the seeded Sangiovese will be required for their functional validation.

Embryo rescue is an effective method and has been widely applied in the breeding of seedless grape. In this study, we conducted eight cross combinations involving five stenospermocarpic seedless grape varieties, with the male parents being the variety ‘Beichun’ and a seedless variety ‘Venus Seedless’. The young fruits of the resulting hybrid plants were harvested at the optimal sampling time for each female parent and subjected to in vitro ovule culture. To enhance the efficiency of the seedless grape embryo rescue technology system, we conducted a comparative analysis on the impact of solid and solid-liquid diphasic MM3 embryo development medium, various parental genotypes, and the duration of ovule culture on embryo rescue. Additionally, marker assisted-selection (MAS), was employed on the hybrids using the seedless gene molecular marker SCF27-2000. Results revealed variability in the impact of medium phase on the successful rescue of embryos across different cross combination. Cultivars ‘Perlette’ and ‘Qinhong No.1’ emerged as suitable female parents for successful embryo rescue. Notably, the influence of the maternal genotype on embryo rescue exceeded that of the paternal genotype and medium phase. The rates of embryo development, growth, and seedling formation for the combinations ‘Perlette’ × ‘Venus Seedless’ and ‘Qinhong No.1’ × ‘Venus Seedless’ peaked at 10 weeks of ovule culture. A total of 894 hybrid strains resulting from eight cross combinations were obtained through embryo rescue, which 559 strains exhibiting a seedless marker, yielding an average seedless rate of 62.53%.Key messageThe study investigated the influencing factors in embryo rescue for seedless grapes, resulting in the identification of 559 strains carrying the seedless gene molecular marker SCF27-2000.

Key messageThe seedless mutant tn-1 in chili pepper is caused by a mutation in CaCKI1 (CA12g21620), which encodes histidine kinase involving female gametophyte development. An amino acid insertion in the receiver domain of CaCKI1 may be the mutation responsible for tn-1.Seedlessness is a desirable trait in fruit crops because the removal of seeds is a troublesome step for consumers and processing industries. However, little knowledge is available to develop seedless chili peppers. In a previous study, a chili pepper mutant tn-1, which stably produces seedless fruits, was isolated. In this study, we report characterization of tn-1 and identification of the causative gene. Although pollen germination was normal, confocal laser microscopy observations revealed deficiency in embryo sac development in tn-1. By marker analysis, the tn-1 locus was narrowed down to a 313 kb region on chromosome 12. Further analysis combined with mapping-by-sequencing identified CA12g21620, which encodes histidine kinase as a candidate gene. Phylogenetic analysis revealed CA12g21620 was the homolog of Arabidopsis CKI1 (Cytokinin Independent 1), which plays an important role in female gametophyte development, and CA12g21620 was designated as CaCKI1. Sequence analysis revealed that tn-1 has a 3-bp insertion in the 6th exon resulting in one lysine (K) residue insertion in receiver domain of CaCKI1, and the sequence nearby the insertion is widely conserved among CKI1 orthologs in various plants. This suggested that one K residue insertion may reduce the phosphorylation relay downstream of CaCKI1 and impair normal development of female gametophyte, resulting in seedless fruits production in tn-1. Furthermore, we demonstrated that virus-induced gene silencing of CaCKI1 reduced normally developed female gametophyte in chili pepper. This study describes the significant role of CaCKI1 in seed development in chili pepper and the possibility of developing seedless cultivars using its mutation.

Key message Abnormal expression of genes regulating anther and pollen development and insufficient accumulation of male sterility (MS)- related metabolites lead to MS in cybrid pummelo Male sterility (MS) is a major cause of seedlessness in citrus, which is an important trait for fresh fruit. Understanding the mechanism of MS is important for breeding seedless citrus cultivars. In this study, we dissected the transcriptional, metabolic and physiological mechanisms of MS in somatic cybrid of pummelo (G1 + HBP). G1 + HBP exhibited severe male sterility, manifesting as retarded anther differentiation, abnormal anther wall development (especially tapetum and endothecium), and deficient pollen wall formation. In the anthers of G1 + HBP, the expression of genes regulating anther differentiation and tapetum development was abnormal, and the expression of genes regulating endothecium secondary lignification thickening and pollen wall formation was down-regulated. The transcription of genes involved in MS-related biological processes, such as jasmonic acid (JA) signaling pathway, primary metabolism, flavonoid metabolism, and programmed cell death, was altered in G1 + HBP anthers, and the accumulation of MS-associated metabolites, including fatty acids, amino acids, sugars, ATP, flavonols and reactive oxygen species (ROS), was down-regulated in G1 + HBP anthers. In summary, abnormal expression of key genes regulating anther and pollen development, altered transcription of key genes involved in MS-related metabolic pathways, and insufficient accumulation of MS-related metabolites together lead to MS in G1 + HBP. The critical genes and the metabolism pathways identified herein provide new insights into the formation mechanism of MS in citrus and candidate genes for breeding seedless citrus.

Male sterility is an important trait for breeding and for the seedless fruit production in citrus. We identified one seedling which exhibiting male sterility and seedlessness (named ms1 hereafter), from a cross between two fertile parents, with sour orange ( Citrus aurantium ) as seed parent and Ponkan mandarin ( Citrus reticulata ) as pollen parent. Analysis using pollen viability staining, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) revealed that the mature pollen of the ms1 was aborted, displaying collapse and deformity. Further cytological analysis identified the abnormal formation of monad, dyad, and tetrad instead of the normal tetrad formation, leading to meiotic failure in the seedless hybrid. By comparative transcript profiling of meiotic anther of fertile and sterile hybrids, we observed significant downregulation of CYCA1;2 ( TAM ) and OSD1 genes in the hybrid, which known to control the transition from meiosis I to meiosis II in plants. These results indicated abnormal meiosis led to the male sterility of the seedless hybrid and that the decreased activities of kinases and cyclins may associated with the failure of the transition of meiosis I to meiosis II during anthers development.

Seedlessness in grapes is much appreciated by consumers and especially in cultivars consumed either as table grapes or as raisins. In many parts of the world, low temperature is the main environmental stress limiting grape production. In this study, stenospermocarpic (seed abortion) cultivars were selected as the female parents while seeded cold-resistant cultivars were selected as the male parents to develop new cold-resistant seedless grapes using embryo rescue technology, which has previously been shown to be a highly efficient way of breeding seedless grapes. Here, we report optima in genotype, sampling time, and culture medium for the embryo rescue of 14 hybrid combinations. Our results indicate that the embryo development rate (39.9%) and the seedlings rate (21.5%) were highest among the 14 crosses when ‘Ruby Seedless’ was used as the female parent and ‘Beibinghong’ was used as the male parent. The best sampling times for ‘Yuehong Wuhe’, ‘Ruby Seedless’, and ‘Melissa seedless’ were 37, 55, and 52 days after flowering, respectively. Embryo rescue efficiency was highest when the sucrose concentration for seedlings was maintained at about 1.0%. Using molecular markers, we detected 91 hybrids with seedless traits and 18 hybrids with cold resistance traits.

1. Whilst most studies reviewing the reliance of global agriculture on insect pollination advocate increasing the 'supply' of pollinators (wild or managed) to improve crop yields, there has been little focus on altering a crop's 'demand' for pollinators. 2. Parthenocarpy (fruit set in the absence of fertilization) is a trait which can increase fruit quantity and quality from pollinator-dependent crops by removing the need for pollination. 3. Here we present a meta-analysis of studies examining the extent and effectiveness of parthenocarpy-promoting techniques (genetic modification, hormone application and selective breeding) currently being used commercially, or experimentally, on pollinator-dependent crops in different test environments (no pollination, hand pollination, open pollination). 4. All techniques significantly increased fruit quantity and quality in 18 pollinator-dependent crop species (not including seed and nut crops as parthenocarpy causes seedlessness). The degree to which plants experienced pollen limitation in the different test environments could not be ascertained, so the absolute effect of parthenocarpy relative to optimal pollination could not be determined. 5. Synthesis and applications. Parthenocarpy has the potential to lower a crop's demand for pollinators, whilst extending current geographic and climatic ranges of production. Thus, growers may wish to use parthenocarpic crop plants, in combination with other environmentally considerate practices, to improve food security and their economic prospects.

Background Grapevine ( Vitis vinifera L.) is the most important Mediterranean fruit crop, used to produce both wine and spirits as well as table grape and raisins. Wine and table grape cultivars represent two divergent germplasm pools with different origins and domestication history, as well as differential characteristics for berry size, cluster architecture and berry chemical profile, among others. ‘Sultanina’ plays a pivotal role in modern table grape breeding providing the main source of seedlessness. This cultivar is also one of the most planted for fresh consumption and raisins production. Given its importance, we sequenced it and implemented a novel strategy for the de novo assembly of its highly heterozygous genome. Results Our approach produced a draft genome of 466 Mb, recovering 82% of the genes present in the grapevine reference genome; in addition, we identified 240 novel genes. A large number of structural variants and SNPs were identified. Among them, 45 (21 SNPs and 24 INDELs) were experimentally confirmed in ‘Sultanina’ and six SNPs in other 23 table grape varieties. Transposable elements corresponded to ca. 80% of the repetitive sequences involved in structural variants and more than 2,000 genes were affected in their structure by these variants. Some of these genes are likely involved in embryo development, suggesting that they may contribute to seedlessness, a key trait for table grapes. Conclusions This work produced the first structural variants and SNPs catalog for grapevine, constituting a novel and very powerful tool for genomic studies in this key fruit crop, particularly useful to support marker assisted breeding in table grapes.