Transcriptomic analysis of short-fruit 1 (sf1) reveals new insights into the variation of fruit-related traits in Cucumis sativus

Combined BSA-Seq and RNA-Seq to Identify Potential Genes Regulating Fruit Size in Bottle Gourd (Lagenaria siceraria L.)

Fruit size is a crucial agronomic trait in bottle gourd, impacting both yield and utility. Despite its significance, the regulatory mechanism governing fruit size in bottle gourd remains largely unknown. In this study, we used bottle gourd (small-fruited H28 and large-fruited H17) parent plants to measure the width and length of fruits at various developmental stages, revealing a single 'S' growth curve for fruit expansion. Paraffin section observations indicated that both cell number and size significantly influence bottle gourd fruit size. Through bulked segregant analysis and combined genotype-phenotype analysis, the candidate interval regulating fruit size was pinpointed to 17,747,353 bp-18,185,825 bp on chromosome 9, encompassing 0.44 Mb and including 44 genes. Parental fruits in the rapid expansion stage were subjected to RNA-seq, highlighting that differentially expressed genes were mainly enriched in pathways related to cell wall biosynthesis, sugar metabolism, and hormone signaling. Transcriptome and resequencing analysis, combined with gene function annotation, identified six genes within the localized region as potential regulators of fruit size. This study not only maps the candidate interval of genes influencing fruit size in bottle gourd through forward genetics, but also offers new insights into the potential molecular mechanisms underlying this trait through transcriptome analysis.

Cytological and Transcriptome Analyses Provide Insights into Persimmon Fruit Size Formation (Diospyros kaki Thunb.)

Persimmon (Diospyros kaki Thunb.) fruit size variation is abundant. Studying the size of the persimmon fruit is helpful in improving its economic value. At present, the regulatory mechanism of persimmon fruit size formation is still unclear. In this study, the mechanism of fruit size formation was investigated through morphological, cytological and transcriptomic analyses, as well as exogenous ethrel and aminoethoxyinylglycine (AVG: ethylene inhibitor) experiments using the large fruit and small fruit of 'Yaoxianwuhua'. The results showed that stages 3-4 (June 11-June 25) are the crucial morphological period for differentiation of large fruit and small fruit in persimmon. At this crucial morphological period, the cell number in large fruit was significantly more than that in small fruit, indicating that the difference in cell number is the main reason for the differentiation of persimmon fruit size. The difference in cell number was caused by cell division. CNR1, ANT, LAC17 and EB1C, associated with cell division, may be involved in regulating persimmon fruit size. Exogenous ethrel resulted in a decrease in fruit weight, and AVG treatment had the opposite effect. In addition, LAC17 and ERF114 were upregulated after ethrel treatment. These results indicated that high ethylene levels can reduce persimmon fruit size, possibly by inhibiting cell division. This study provides valuable information for understanding the regulation mechanism of persimmon fruit size and lays a foundation for subsequent breeding and artificial regulation of fruit size.

How different of the rhizospheric and endophytic microbial compositions in watermelons with different fruit shapes

Fruit shape is an important character of watermelon. And the compositions of rhizospheric and endophytic microorganisms of watermelon with different fruit shape also remains unclear. To elucidate the biological mechanism of watermelon fruit shape formations, the rhizospheric and endophytic microbial community compositions between oval (OW) and circular watermelons (CW) were analyzed. The results showed that except of the rhizospheric bacterial richness (P < 0.05), the rhizospheric and endophytic microbial (bacterial and fungal) diversity were not statistically significant between OW and CW (P > 0.05). However, the endophytic microbial (bacterial and fungal) compositions were significantly different. Firstly, Bacillus, Rhodanobacter, Cupriavidus, Luteimonas, and Devosia were the unique soil dominant bacterial genera in rhizospheres of circular watermelon (CW); In contrast, Nocardioides, Ensifer, and Saccharomonospora were the special soil dominant bacterial genera in rhizospheres of oval watermelons (OW); Meanwhile, Cephalotrichum, Neocosmospora, Phialosimplex, and Papulaspora were the unique soil dominant fungal genera in rhizospheres of circular watermelon (CW); By contrast, Acremonium, Cladosporium, Cryptococcus_f__Tremellaceae, Sodiomyces, Microascus, Conocybe, Sporidiobolus, and Acremonium were the unique soil dominant fungal genera in rhizospheres of oval watermelons (OW). Additionally, Lechevalieria, Pseudorhodoferax, Pseudomonas, Massilia, Flavobacterium, Aeromicrobium, Stenotrophomonas, Pseudonocardia, Novosphingobium, Melittangium, and Herpetosiphon were the unique dominant endophytic bacterial genera in stems of CW; In contrast, Falsirhodobacter, Kocuria, and Kineosporia were the special dominant endophytic genera in stems of OW; Moreover, Lectera and Fusarium were the unique dominant endophytic fungal genera in stems of CW; By contrast, Cercospora only was the special dominant endophytic fungal genus in stems of OW. All above results suggested that watermelons with different fruit shapes exactly recruited various microorganisms in rhizospheres and stems. Meanwhile, the enrichments of the different rhizosphric and endophytic microorganisms could be speculated in relating to watermelon fruit shapes formation.

Comparative Transcriptome Analysis Reveals the Molecular Basis of Brassica napus in Response to Aphid Stress

Rapeseed is a globally important economic crop that can be severely impacted by aphids. However, our understanding of rapeseed resistance to aphid stress is very limited. In this study, we analyzed the resistance characteristics of the low aphid-susceptible variety APL01 and the highly aphid-susceptible variety Holly in response to aphid stress. APL01 had a more significant inhibitory effect on aphid proliferation compared with Holly during the early stage of inoculation, whereas Holly showed stronger tolerance to aphid stress compared with APL01 during the later stage of inoculation. Through transcriptome, physiological, and gene expression analyses, it was revealed that chitinase activity, catalase activity, calcium signal transduction, and activation of systemic acquired resistance might be involved in aphid resistance in B. napus. The degree of inhibition of photosynthesis in plants under aphid stress directly determines the tolerance of B. napus to aphid stress. Furthermore, four promising candidate genes were screened from eight genes related to rapeseed response to biotic stress through RT-qPCR analysis of gene expression levels. These research findings represent an important step forward in understanding the resistance of rapeseed to aphid stress and provide a solid foundation for the cloning of genes responsible for this resistance.

Mapping and identification of CsSF4, a gene encoding a UDP-N-acetyl glucosamine-peptide N-acetylglucosaminyltransferase required for fruit elongation in cucumber (Cucumis sativus L.)

The short fruit length phenotype in sf4 is caused by a SNP in Csa1G665390, which encodes an O-linked N-acetylglucosamine (GlcNAc) transferase in cucumber. Cucumber fruit is an excellent resource for studying fruit morphology due to its fast growth rate and naturally abundant morphological variations. The regulatory mechanisms underlying plant organ size and shape are important and fundamental biological questions. In this study, a short-fruit length mutant, sf4, was identified from an ethyl methanesulfonate (EMS) mutagenesis population derived from the North China-type cucumber inbred line WD1. Genetic analysis indicated that the short fruit length phenotype of sf4 was controlled by a recessive nuclear gene. The SF4 locus was located in a 116.7-kb genomic region between the SNP markers GCSNP75 and GCSNP82 on chromosome 1. Genomic and cDNA sequences analysis indicated that a single G to A transition at the last nucleotide of Csa1G665390 intron 21 in sf4 changed the splice site from GT-AG to GT-AA, resulting in a 42-bp deletion in exon 22. Csa1G665390 is presumed to be a candidate gene, CsSF4 that encodes an O-linked N-acetylglucosamine (GlcNAc) transferase (OGT). CsSF4 was highly expressed in the leaves and male flowers of wild-type cucumbers. Transcriptome analysis indicated that sf4 had alterations in expression of many genes involved in hormone response pathways, cell cycle regulation, DNA replication, and cell division, suggesting that cell proliferation-associated gene networks regulate fruit development in cucumber. Identification of CsSF4 will contribute to elucidating the function of OGT in cell proliferation and to understanding fruit elongation mechanisms in cucumber.

Identification of Bottle Gourd (Lagenaria siceraria) OVATE Family Genes and Functional Characterization of LsOVATE1

The OVATE gene family is a class of conserved transcription factors that play significant roles in plant growth, development, and abiotic stress, and also affect fruit shape in vegetable crops. Bottle gourd (Lagenaria siceraria), commonly known as calabash or gourd, is an annual climber belonging to the Cucurbitaceae family. Studies on bottle gourd OVATE genes are limited. In this study, we performed genome-wide identification of the OVATE gene family in bottle gourd, and identified a total of 20 OVATE family genes. The identified genes were unevenly distributed across 11 bottle gourd chromosomes. We also analyzed the gene homology, amino acid sequence conservation, and three-dimensional protein structure (via prediction) of the 20 OVATE family genes. We used RNA-seq data to perform expression analysis, which found 20 OVATE family genes to be differentially expressed based on spatial and temporal characteristics, suggesting that they have varying functions in the growth and development of bottle gourd. In situ hybridization and subcellular localization analysis showed that the expression characteristics of the LsOVATE1 gene, located on chromosome 7 homologous to OVATE, is a candidate gene for affecting the fruit shape of bottle gourd. In addition, RT-qPCR data from bottle gourd roots, stems, leaves, and flowers showed different spatial expression of the LsOVATE1 gene. The ectopic expression of LsOVATE1 in tomato generated a phenotype with a distinct fruit shape and development. Transgenic-positive plants that overexpressed LsOVATE1 had cone-shaped fruit, calyx hypertrophy, petal degeneration, and petal retention after flowering. Our results indicate that LsOVATE1 could serve important roles in bottle gourd development and fruit shape determination, and provide a basis for future research into the function of LsOVATE1.

Relationship between Key Environmental Factors and the Architecture of Fruit Shape and Size in Near-Isogenic Lines of Cucumber (Cucumis sativus L.)

Fruit shape and size are complex traits influenced by numerous factors, especially genetics and environment factors. To explore the mechanism of fruit shape and size development in cucumber, a pair of near-isogenic lines (NIL) Ln35 and Ln37 were used. The fruit length and diameter, cell length and diameter, and related gene expression were measured. Both the fruit length, diameter, and cell length and diameter showed sigmate curves in the two lines. The cell length and diameter were significantly positively correlated with fruit length and diameter both in two lines. The expression of CsACS2 and CsLNG showed significant positive correlations with fruit length and diameter increment in Ln35, and there was no correlation in Ln37. Furthermore, there were significant positive correlations between fruit size and thermal effectiveness (TE), as well as between fruit size and photosynthetic active radiation (PAR), both in two lines. Two models using logistic regression were formulated to assess the relationships among fruit length and diameter in Ln35 and Ln37, respectively, based on thermal effectiveness and photosynthetic active radiation (TEP). The coefficient R² values of the models were 0.977 and 0.976 in Ln35, and 0.987 and 0.981 in Ln37, respectively. The root mean square error (RMSE) was 12.012 mm and 4.338 mm in Ln35, and 5.17 mm and 7.082 mm in Ln37, respectively, which illustrated the accurate and efficient of these models. These biologically interpreted parameters will provide precision management for monitoring fruit growth and forecasting the time of harvesting under different temperatures and light conditions.

Ectopic Expression of CsSUN in Tomato Results in Elongated Fruit Shape via Regulation of Longitudinal Cell Division

Fruit shape, an important agronomic trait of cucumber (Cucumis sativus L.), is tightly controlled by a series of genes such as CsSUN, a homologue of SlSUN that is responsible for the tomato (Solanum lycopersicum) fruit shape via the modulation of cell division. However, the direct genetic evidence about the CsSUN-mediated regulation of fruit shape is still scarce, limiting our mechanistic understanding of the biological functions of CsSUN. Here, we introduced CsSUN into the round-fruited tomato inbred line ‘SN1′ (wild type, WT) via the Agrobacterium tumefaciens-mediated method. The high and constitutive expression of CsSUN was revealed by real-time PCR in all the tested tissues of the transgenic plants, especially in the fruits and ovaries. Phenotypic analyses showed that the ectopic expression of CsSUN increased fruit length while it decreased fruit diameter, thus leading to the enhanced fruit shape index in the transgenic tomato lines relative to the WT. Additionally, the reduction in the seed size and seed-setting rate and the stimulation of seed germination were observed in the CsSUN-expressed tomato. A histological survey demonstrated that the elongated fruits were mainly derived from the significant increasing of the longitudinal cell number, which compensated for the negative effects of decreased cell area in the central columellae. These observations are different from action mode of SlSUN, thus shedding new insights into the SUN-mediated regulation of fruit shape.

Serial-Omics and Molecular Function Study Provide Novel Insight into Cucumber Variety Improvement

Cucumbers are rich in vitamins and minerals. The cucumber has recently become one of China’s main vegetable crops. More specifically, the adjustment of the Chinese agricultural industry’s structure and rapid economic development have resulted in increases in the planting area allocated to Chinese cucumber varieties and in the number of Chinese cucumber varieties. After complete sequencing of the “Chinese long” genome, the transcriptome, proteome, and metabolome were obtained. Cucumber has a small genome and short growing cycle, and these traits are conducive to the application of molecular breeding techniques for improving fruit quality. Here, we review the developments and applications of molecular markers and genetic maps for cucumber breeding and introduce the functions of gene families from the perspective of genomics, including fruit development and quality, hormone response, resistance to abiotic stress, epitomizing the development of other omics, and relationships among functions.

Morphological Characterization and Integrated Transcriptome and Proteome Analysis of Organ Development Defective 1 (odd1) Mutant in Cucumis sativus L

Cucumber (Cucumis sativus L.) is an economically important vegetable crop with the unique growth habit and typical trailing shoot architecture of Cucurbitaceae. Elucidating the regulatory mechanisms of growth and development is significant for improving quality and productivity in cucumber. Here we isolated a spontaneous cucumber mutant organ development defective 1 (odd1) with multiple morphological changes including root, plant stature, stem, leaf, male and female flowers, as well as fruit. Anatomical and cytological analyses demonstrated that both cell size and number decreased, and the shoot apical meristem (SAM) was smaller in odd1 compared with WT. Pollen vigor and germination assays and cross tests revealed that odd1 is female sterile, which may be caused by the absence of ovules. Genetic analysis showed that odd1 is a recessive single gene mutant. Using the MutMap strategy, the odd1 gene was found to be located on chromosome 5. Integrated profiling of transcriptome and proteome indicated that the different expression genes related to hormones and SAM maintenance might be the reason for the phenotypic changes of odd1. These results expanded the insight into the molecular regulation of organ growth and development and provided a comprehensive reference map for further studies in cucumber.

Genome-wide association study of the candidate genes for grape berry shape-related traits

BACKGROUND

In the breeding of new horticultural crops, fruit shape is an important selection characteristic. A variety of fruit shapes appeared during the gradual process of selection and domestication. However, few studies have been conducted on grape berry shape, especially studies related to mining candidate genes. To discover candidate genes related to grape berry shape, the present study first took the berry shape parameters analyzed by Tomato Analyzer as the target traits and used a genome-wide association analysis to analyze candidate genes.

RESULTS

In total, 122 single-nucleotide polymorphism (SNP) loci had significant correlations with multiple berry shape traits in both years, and some candidate genes were further mined. These genes were mainly related to LRR receptor-like serine/threonine-protein kinase (At1g05700 and At1g07650), transcription factors (GATA transcription factor 23-like, transcription factor VIP1, transcription initiation factor TFIID, and MADS-box transcription factor 6), ubiquitin ligases (F-box protein SKIP19 and RING finger protein 44), and plant hormones (indole-3-acetic acid-amido synthetase GH3.6 and ethylene-responsive transcription factor ERF061). In addition, some important SNP loci were associated with multiple berry-shape traits. The study further revealed some genes that control multiple traits simultaneously, indicating that these berry shape traits are subject to the coordinated regulation of some genes in controlling berry shape.

CONCLUSIONS

In the present work, we identified interesting genetic determinants of grape berry shape-related traits. The identification of molecular markers that are closely related to these berry-shape traits is of great significance for breeding specific berry-shaped grape varieties.

Cucurbitaceae genome evolution, gene function and molecular breeding

The Cucurbitaceae is one of the most genetically diverse plant families in the world. Many of them are important vegetables or medicinal plants and are widely distributed worldwide. The rapid development of sequencing technologies and bioinformatic algorithms has enabled the generation of genome sequences of numerous important Cucurbitaceae species. This has greatly facilitated research on gene identification, genome evolution, genetic variation and molecular breeding of cucurbit crops. So far, genome sequences of 18 different cucurbit species belonging to tribes Benincaseae, Cucurbiteae, Sicyoeae, Momordiceae and Siraitieae have been deciphered. This review summarizes the genome sequence information, evolutionary relationship, and functional genes associated with important agronomic traits (e.g., fruit quality). The progress of molecular breeding in cucurbit crops and prospects for future applications of Cucurbitaceae genome information are also discussed.

Localization of quantitative trait loci for cucumber fruit shape by a population of chromosome segment substitution lines

Cucumber fruit shape, a significant agronomic trait, is controlled by quantitative trait loci (QTLs). Feasibility of chromosome segment substitution lines (CSSLs) is well demonstrated to map QTLs, especially the minor-effect ones. To detect and identify QTLs with CSSLs can provide new insights into the underlying mechanisms regarding cucumber fruit shape. In the present study, 71 CSSLs were built from a population of backcross progeny (BC4F2) by using RNS7 (a round-fruit cucumber) as the recurrent parent and CNS21 (a long-stick-fruit cucumber) as the donor parent in order to globally detect QTLs for cucumber fruit shape. With the aid of 114 InDel markers covering the whole cucumber genome, 21 QTLs were detected for fruit shape-related traits including ovary length, ovary diameter, ovary shape index, immature fruit length, immature fruit diameter, immature fruit shape index, mature fruit length, mature fruit diameter and mature fruit shape index, and 4 QTLs for other traits including fruit ground and flesh color, and seed size were detected as well. Together our results provide important resources for the subsequent theoretical and applied researches on cucumber fruit shape and other traits.

Cucumber Fruit Size and Shape Variations Explored from the Aspects of Morphology, Histology, and Endogenous Hormones

Fruit size and shape are important qualities and yield traits in cucumber (Cucumis sativus L.), but the factors that influence fruit size and shape remain to be explored. In this study, we investigated the dynamic changes of fruit size and shape from the aspects of morphology, cellular levels and endogenous hormones for nine typical cucumber inbred lines. The results show that fruit length had a strong positive correlation to the cell number in the longitudinal section of fruit throughout the four stages of 0, 6, 12, and 30 DAA (days after anthesis). However, the significant negative correlations were found between fruit length and the fruit cell size at 12 and 30 DAA. Furthermore, fruit diameter was positively correlated to the cell number in the cross section at all the investigated fruit growth stages. The indole-3-acetic acid (IAA) content showed significant positive correlations to the fruit length at all fruit growth stages of −6, −3, 0, 3, 6, 9 and 12 DAA, but IAA content and fruit diameter showed significant negative correlations for all the stages except for at −6 DAA. The trans-zeatin riboside (tZR), zeatin (ZT), gibberellic acid (GA₃) and jasmonic acid (JA) content had a positive or negative correlation with fruit length or diameter only at certain stages. Neither fruit length nor diameter had significant correlations to abscisic acid (ABA) content. These results indicate that variations in fruit size and shape of different cucumber inbred lines mainly result from the differences in fruit cell number and endogenous IAA content. The present work is the first to propose cucumber fruit size and shape changes from the combined aspects of morphology, cellular levels, and endogenous hormones.

Origin and domestication of Cucurbitaceae crops: insights from phylogenies, genomics and archaeology

Some of the World's most valuable crops, including watermelon, honey melon, cucumber, squash, zucchini and pumpkin, belong to the family Cucurbitaceae. We review insights on their domestication from new phylogenies, archaeology and genomic studies. Ancestral state estimation on the most complete Cucurbitaceae phylogeny to date suggests that an annual life cycle may have contributed to domestication. Domestication started c. 11 000 years ago in the New World and Asia, and apparently more recently in Africa. Some cucurbit crops were domesticated only once, others multiple times (e.g. melon from different Asian and African populations). Most wild cucurbit fruits are bitter and nonpalatable to humans, and nonbitterness of the pulp apparently was a trait favoured early during domestication, with genomic data showing how bitterness loss was achieved convergently. The genetic pathways underlying lycopene accumulation, red or orange pulp colour, and fruit size and shape are only just beginning to be understood. The study of cucurbit domestication in recent years has benefitted from the increasing integration of archaeological and genomic data with insights from herbarium collections, the most efficient way to understand species' natural geographic ranges and climate adaptations.

Comparative Transcriptomic Analysis of Two Bottle Gourd Accessions Differing in Fruit Size

The bottle gourd (Lagenaria siceraria) is an important horticultural and medicinal crop with high nutritional value. This study aimed at examining the molecular regulation of fruit size in bottle gourd. We performed transcriptome sequencing of two bottle gourd cultivars differing in their fruit size. The average fruit length and weight of the cultivar Hang (39.48 cm/624.4 g) were higher than those of the cultivar USA (10.34 cm/152.8 g) at maturity. Transcriptome sequencing and assembly resulted in 89,347 unigenes. A total of 1250 differentially expressed genes (DEG) were found between the two cultivars, including 422 upregulated genes and 828 downregulated genes in Hang as compared to USA. Genes related to cell wall metabolism, phytohormones, cell cycle, and cell division showed significant differential expression between the two cultivars. DEGs encoding transcription factors (TF) from nine TF families were also identified. The ethylene response factor family was the most enriched among these families. Our study provides a basis for further investigations of the molecular regulation of fruit size in bottle gourd.

Molecularly tagged genes and quantitative trait loci in cucumber with recommendations for QTL nomenclature

Cucumber, Cucumis sativus L. (2n = 2x = 14), is an important vegetable crop worldwide. It was the first specialty crop with a publicly available draft genome. Its relatively small, diploid genome, short life cycle, and self-compatible mating system offers advantages for genetic studies. In recent years, significant progress has been made in molecular mapping, and identification of genes and QTL responsible for key phenotypic traits, but a systematic review of the work is lacking. Here, we conducted an extensive literature review on mutants, genes and QTL that have been molecularly mapped or characterized in cucumber. We documented 81 simply inherited trait genes or major-effect QTL that have been cloned or fine mapped. For each gene, detailed information was compiled including chromosome locations, allelic variants and associated polymorphisms, predicted functions, and diagnostic markers that could be used for marker-assisted selection in cucumber breeding. We also documented 322 QTL for 42 quantitative traits, including 109 for disease resistances against seven pathogens. By alignment of these QTL on the latest version of cucumber draft genomes, consensus QTL across multiple studies were inferred, which provided insights into heritable correlations among different traits. Through collaborative efforts among public and private cucumber researchers, we identified 130 quantitative traits and developed a set of recommendations for QTL nomenclature in cucumber. This is the first attempt to systematically summarize, analyze and inventory cucumber mutants, cloned or mapped genes and QTL, which should be a useful resource for the cucurbit research community.

Genetic architecture of fruit size and shape variation in cucurbits: a comparative perspective

The Cucurbitaceae family hosts many economically important fruit vegetables (cucurbits) such as cucumber, melon, watermelon, pumpkin/squash, and various gourds. The cucurbits are probably best known for the diverse fruit sizes and shapes, but little is known about their genetic basis and molecular regulation. Here, we reviewed the literature on fruit size (FS), shape (FSI), and fruit weight (FW) QTL identified in cucumber, melon, and watermelon, from which 150 consensus QTL for these traits were inferred. Genome-wide survey of the three cucurbit genomes identified 253 homologs of eight classes of fruit or grain size/weight-related genes cloned in Arabidopsis, tomato, and rice that encode proteins containing the characteristic CNR (cell number regulator), CSR (cell size regulator), CYP78A (cytochrome P450), SUN, OVATE, TRM (TONNEAU1 Recruiting Motif), YABBY, and WOX domains. Alignment of the consensus QTL with candidate gene homologs revealed widespread structure and function conservation of fruit size/shape gene homologs in cucurbits, which was exemplified with the fruit size/shape candidate genes CsSUN25-26-27a and CsTRM5 in cucumber, CmOFP1a in melon, and ClSUN25-26-27a in watermelon. In cucurbits, the andromonoecy (for 1-aminocyclopropane-1-carboxylate synthase) and the carpel number (for CLAVATA3) loci are known to have pleiotropic effects on fruit shape, which may complicate identification of fruit size/shape candidate genes in these regions. The present work illustrates the power of comparative analysis in understanding the genetic architecture of fruit size/shape variation, which may facilitate QTL mapping and cloning for fruit size-related traits in cucurbits. The limitations and perspectives of this approach are also discussed.

Molecular basis of cucumber fruit domestication

Cucumber (Cucumis sativus L.) is an economically important vegetable crop that is cultivated worldwide. Compared to the wild ancestor bearing small, bitter and seedy fruit, domesticated cucumbers exhibit significant variation in fruit appearance, size and flavor. Understanding the molecular basis of domestication related traits can provide insights into fruit evolution and make crop breeding more efficient. Here we review recent advances in relating to the genetic basis of fruit morphological traits (femaleness, fruit spine, wart, size, color and carpel development) and organoleptic features (bitterness) during cucumber domestication.

MicroRNAs and their targets in cucumber shoot apices in response to temperature and photoperiod

BACKGROUND

The cucumber is one of the most important vegetables worldwide and is used as a research model for study of phloem transport, sex determination and temperature-photoperiod physiology. The shoot apex is the most important plant tissue in which the cell fate and organ meristems have been determined. In this study, a series of whole-genome small RNA, degradome and transcriptome analyses were performed on cucumber shoot apical tissues treated with high vs. low temperature and long vs. short photoperiod.

RESULTS

A total of 164 known miRNAs derived from 68 families and 203 novel miRNAs from 182 families were identified. Their 4611 targets were predicted using psRobot and TargetFinder, amongst which 349 were validated by degradome sequencing. Fourteen targets of six miRNAs were differentially expressed between the treatments. A total of eight known and 16 novel miRNAs were affected by temperature and photoperiod. Functional annotations revealed that "Plant hormone signal transduction" pathway was significantly over-represented in the miRNA targets. The miR156/157/SBP-Boxes and novel-mir153/ethylene-responsive transcription factor/senescence-related protein/aminotransferase/acyl-CoA thioesterase are the two most credible miRNA/targets combinations modulating the plant's responsive processes to the temperature-photoperiod changes. Moreover, the newly evolved, cucumber-specific novel miRNA (novel-mir153) was found to target 2087 mRNAs by prediction and has 232 targets proven by degradome analysis, accounting for 45.26-58.88% of the total miRNA targets in this plant. This is the largest sum of genes targeted by a single miRNA to the best of our knowledge.

CONCLUSIONS

These results contribute to a better understanding of the miRNAs mediating plant adaptation to combinations of temperature and photoperiod and sheds light on the recent evolution of new miRNAs in cucumber.

Genetic mapping reveals a candidate gene (ClFS1) for fruit shape in watermelon (Citrullus lanatus L.)

A 159 bp deletion in ClFS1 gene encoding IQD protein is responsible for fruit shape in watermelon. Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] is known for its rich diversity in fruit size and shape. Fruit shape has been one of the major objectives of watermelon breeding. However, the candidate genes and the underlying genetic mechanism for such an important trait in watermelon are unknown. In this study, we identified a locus on chromosome 3 of watermelon genome controlling fruit shape. Segregation analysis in F₂ and BC₁ populations derived from a cross between two inbred lines "Duan125" (elongate fruit) and "Zhengzhouzigua" (spherical fruit) suggests that fruit shape of watermelon is controlled by a single locus and elongate fruit (OO) is incompletely dominant to spherical fruit (oo) with the heterozygote (Oo) being oval fruit. GWAS profiles among 315 accessions identified a major locus designated on watermelon chromosome 3, which was confirmed by BSA-seq mapping in the F₂ population. The candidate gene was mapped to a region 46 kb on chromosome 3. There were only four genes present in the corresponding region in the reference genome. Four candidate genes were sequenced in this region, revealing that the CDS of Cla011257 had a 159 bp deletion which resulted in the omission of 53 amino acids in elongate watermelon. An indel marker was derived from the 159 bp deletion to test the F₂ population and 105 watermelon accessions. The results showed that Cla011257 cosegregated with watermelon fruit shape. In addition, the Cla011257 expression was the highest at ovary formation stage. The predicted protein of the Cla011257 gene fitted in IQD protein family which was reported to have association with cell arrays and Ca²⁺-CaM signaling modules. Clear understanding of the genes facilitating the fruit shape along with marker association selection will be an effective way to develop new cultivars.