Comparative transcriptome analysis during early fruit development between three seedy citrus genotypes and their seedless mutants

Abnormal transition from meiosis I to meiosis II induces male sterility in a seedless artificial hybrid of 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.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01521-5.

Gene expression profiles and metabolic pathways responsible for male sterility in cybrid pummelo

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.

Integrative genomics reveals the polygenic basis of seedlessness in grapevine

Seedlessness is a crucial quality trait in table grape (Vitis vinifera L.) breeding. However, the development of seeds involved intricate regulations, and the polygenic basis of seed abortion remains unclear. Here, we combine comparative genomics, population genetics, quantitative genetics, and integrative genomics to unravel the evolution and polygenic basis of seedlessness in grapes. We generated the haplotype-resolved genomes for two seedless grape cultivars, "Thompson Seedless" (TS, syn. "Sultania") and "Black Monukka" (BM). Comparative genomics identified a ∼4.25 Mb hemizygous inversion on Chr10 specific in seedless cultivars, with seedless-associated genes VvTT16 and VvSUS2 located at breakpoints. Population genomic analyses of 548 grapevine accessions revealed two distinct clusters of seedless cultivars, and the identity-by-descent (IBD) results indicated that the origin of the seedlessness trait could be traced back to "Sultania." Introgression, rather than convergent selection, shaped the evolutionary history of seedlessness in grape improvement. Genome-wide association study (GWAS) analysis identified 110 quantitative trait loci (QTLs) associated with 634 candidate genes, including previously unidentified candidate genes, such as three 11S GLOBULIN SEED STORAGE PROTEIN and two CYTOCHROME P450 genes, and well-known genes like VviAGL11. Integrative genomic analyses resulted in 339 core candidate genes categorized into 13 functional categories related to seed development. Machine learning-based genomic selection achieved a remarkable prediction accuracy of 97% for seedlessness in grapevines. Our findings highlight the polygenic nature of seedlessness and provide candidate genes for molecular genetics and an effective prediction for seedlessness in grape genomic breeding.

Full-length transcriptome profiling for fruit development in Diospyros oleifera using nanopore sequencing

OBJECTIVES

Diospyros oleifera, one of the most economically important Diospyros species, is an ideal model for studying the fruit development of persimmon. While, the lack of whole-transcriptome has hindered the complex transcriptional regulation mechanisms of sugar and tannin during fruit development.

DATA DESCRIPTION

We applied Oxford Nanopore Technologies to six developmental stage of fruit from D. oleifera for use in transcriptome sequencing. As a result of full-length transcriptome sequencing, 55.87 Gb of clean data were generated. After mapping onto the reference genome of D. oleifera, 51,588 full-length collapsing transcripts, including 2,727 new gene loci and 43,223 transcripts, were obtained. Comprehensively annotated, 38,086 of new transcripts were functional annotation, and 972 lncRNAs, 7,159 AS events were predicted. Here, we released the transcriptome database of D. oleifera at different stage of fruit development,which will provide a fundamention of to investigatethe transcript structure, variants and evolution of persimmon.

Parthenocarpy-related genes induced by naphthalene acetic acid in oil palm interspecific O × G [Elaeis oleifera (Kunth) Cortés × Elaeis guineensis Jacq.] hybrids

Parthenocarpy is the development without fertilization of seedless fruits. In the oil palm industry, the development of parthenocarpic fruits is considered an attractive option to increase palm oil production. Previous studies have shown the application of synthetic auxins in Elaeis guineensis, and interspecific O×G hybrids (Elaeis oleifera (Kunth) Cortés × E. guineensis Jacq.) induces parthenocarpy. The aim of this study was to identify the molecular mechanism through transcriptomics and biology system approach to responding to how the application of NAA induces parthenocarpic fruits in oil palm O×G hybrids. The transcriptome changes were studied in three phenological stages (PS) of the inflorescences: i) PS 603, pre-anthesis III, ii) PS 607, anthesis, and iii) PS 700, fertilized female flower. Each PS was treated with NAA, Pollen, and control (any application). The expression profile was studied at three separate times: five minutes (T0), 24 hours (T1), and 48 h post-treatment (T2). The RNA sequencing (RNA seq) approach was used with 27 oil palm O×G hybrids for a total of 81 raw samples. RNA-Seq showed around 445,920 genes. Numerous differentially expressed genes (DEGs) were involved in pollination, flowering, seed development, hormone biosynthesis, and signal transduction. The expression of the most relevant transcription factors (TF) families was variable and dependent on the stage and time post-treatment. In general, NAA treatment expressed differentially more genes than Pollen. Indeed, the gene co-expression network of Pollen was built with fewer nodes than the NAA treatment. The transcriptional profiles of Auxin-responsive protein and Gibberellin-regulated genes involved in parthenocarpy phenomena agreed with those previously reported in other species. The expression of 13 DEGs was validated by RT-qPCR analysis. This detailed knowledge about the molecular mechanisms involved in parthenocarpy could be used to facilitate the future development of genome editing techniques that enable the production of parthenocarpic O×G hybrid cultivars without growth regulator application.

A Flashforward Look into Solutions for Fruit and Vegetable Production

One of the most important challenges facing current and future generations is how climate change and continuous population growth adversely affect food security. To address this, the food system needs a complete transformation where more is produced in non-optimal and space-limited areas while reducing negative environmental impacts. Fruits and vegetables, essential for human health, are high-value-added crops, which are grown in both greenhouses and open field environments. Here, we review potential practices to reduce the impact of climate variation and ecosystem damages on fruit and vegetable crop yield, as well as highlight current bottlenecks for indoor and outdoor agrosystems. To obtain sustainability, high-tech greenhouses are increasingly important and biotechnological means are becoming instrumental in designing the crops of tomorrow. We discuss key traits that need to be studied to improve agrosystem sustainability and fruit yield.

Genome-Wide Comprehensive Analysis of the GASA Gene Family in Populus

Gibberellic acid-stimulated Arabidopsis (GASA) proteins, as cysteine-rich peptides (CRPs), play roles in development and reproduction and biotic and abiotic stresses. Although the GASA gene family has been identified in plants, the knowledge about GASAs in Populus euphratica, the woody model plant for studying abiotic stress, remains limited. Here, we referenced the well-sequenced Populus trichocarpa genome, and identified the GASAs in the whole genome of P. euphratica and P. trichocarpa. 21 candidate genes in P. trichocarpa and 19 candidate genes in P. euphratica were identified and categorized into three subfamilies by phylogenetic analysis. Most GASAs with signal peptides were located extracellularly. The GASA genes in Populus have experienced multiple gene duplication events, especially in the subfamily A. The evolution of the subfamily A, with the largest number of members, can be attributed to whole-genome duplication (WGD) and tandem duplication (TD). Collinearity analysis showed that WGD genes played a leading role in the evolution of GASA genes subfamily B. The expression patterns of P. trichocarpa and P. euphratica were investigated using the PlantGenIE database and the real-time quantitative PCR (qRT-PCR), respectively. GASA genes in P. trichocarpa and P. euphratica were mainly expressed in young tissues and organs, and almost rarely expressed in mature leaves. GASA genes in P. euphratica leaves were also widely involved in hormone responses and drought stress responses. GUS activity assay showed that PeuGASA15 was widely present in various organs of the plant, especially in vascular bundles, and was induced by auxin and inhibited by mannitol dramatically. In summary, this present study provides a theoretical foundation for further research on the function of GASA genes in P. euphratica.

Dosage-Dependent Gynoecium Development and Gene Expression in Brassica napus-Orychophragmus violaceus Addition Lines

Distant hybridization usually leads to female sterility of the hybrid but the mechanism behind this is poorly understood. Complete pistil abortion but normal male fertility was shown by one Brassica napus-Orychophragmus violaceus monosomic alien addition line (MA, AACC + 1 IO, 2n = 39) produced previously. To study the effect of a single O. violaceus chromosome addition on pistil development in different genetic backgrounds, hybrids between the MA and B. carinata (BBCC), B. juncea (AABB), and two synthetic hexaploids (AABBCC) were firstly produced in this study which show complete female sterility. A microspore culture was further performed to produce the haploid monosomic alien addition line (HMA, AC + 1 IO, 2n = 20) and disomic addition line (DA, AACC + 2 IO, 2n = 40) together with haploid (H, AC, 2n = 19) and double haploid (DH, AACC, 2n = 38) plants of B. napus from MA to investigate the dosage effect of the alien O. violaceus chromosome on pistil development and gene expression. Compared to MA, the development of the pistils of DA and HMA was completely or partially recovered, in which the pistils could swell and elongate to a normal shape after open pollination, although no seeds were produced. Comparative RNA-seq analyses revealed that the numbers of the differentially expressed genes (DEGs) were significantly different, dosage-dependent, and consistent with the phenotypic difference in pairwise comparisons of HMA vs. H, DA vs. DH, MA vs. DH, MA vs. DA, and MA vs. HMA. The gene ontology (GO) enrichment analysis of DEGs showed that a number of genes involved in the development of the gynoecium, embryo sac, ovule, and integuments. Particularly, several common DEGs for pistil development shared in HMA vs. H and DA vs. DH showed functions in genotoxic stress response, auxin transport, and signaling and adaxial/abaxial axis specification. The results provided updated information for the molecular mechanisms behind the gynoecium development of B. napus responding to the dosage of alien O. violaceus chromosomes.

Decoding the molecular mechanism of parthenocarpy in Musa spp. through protein-protein interaction network

Banana, one of the most important staple fruit among global consumers is highly sterile owing to natural parthenocarpy. Identification of genetic factors responsible for parthenocarpy would facilitate the conventional breeders to improve the seeded accessions. We have constructed Protein-protein interaction (PPI) network through mining differentially expressed genes and the genes used for transgenic studies with respect to parthenocarpy. Based on the topological and pathway enrichment analysis of proteins in PPI network, 12 candidate genes were shortlisted. By further validating these candidate genes in seeded and seedless accession of Musa spp. we put forward MaAGL8, MaMADS16, MaGH3.8, MaMADS29, MaRGA1, MaEXPA1, MaGID1C, MaHK2 and MaBAM1 as possible target genes in the study of natural parthenocarpy. In contrary, expression profile of MaACLB-2 and MaZEP is anticipated to highlight the difference in artificially induced and natural parthenocarpy. By exploring the PPI of validated genes from the network, we postulated a putative pathway that bring insights into the significance of cytokinin mediated CLAVATA(CLV)-WUSHEL(WUS) signaling pathway in addition to gibberellin mediated auxin signaling in parthenocarpy. Our analysis is the first attempt to identify candidate genes and to hypothesize a putative mechanism that bridges the gaps in understanding natural parthenocarpy through PPI network.

PbEIL1 acts upstream of PbCysp1 to regulate ovule senescence in seedless pear

Numerous environmental and endogenous signals control the highly orchestrated and intricate process of plant senescence. Ethylene, a well-known inducer of senescence, has long been considered a key endogenous regulator of leaf and flower senescence, but the molecular mechanism of ethylene-induced ovule senescence has not yet been elucidated. In this study, we found that blockage of fertilization caused ovule abortion in the pear cultivar '1913'. According to transcriptome and phytohormone content data, ethylene biosynthesis was activated by pollination. At the same time, ethylene overaccumulated in ovules, where cells were sensitive to ethylene signals in the absence of fertilization. We identified a transcription factor in the ethylene signal response, ethylene-insensitive 3-like (EIL1), as a likely participant in ovule senescence. Overexpression of PbEIL1 in tomato caused precocious onset of ovule senescence. We further found that EIL1 could directly bind to the promoter of the SENESCENCE-ASSOCIATED CYSTEINE PROTEINASE 1 (PbCysp1) gene and act upstream of senescence. Yeast one-hybrid and dual-luciferase assays revealed the interaction of the transcription factor and the promoter DNA sequence and demonstrated that PbEIL1 enhanced the action of PbCysp1. Collectively, our results provide new insights into how ethylene promotes the progression of unfertilized ovule senescence.

The miR399-CsUBC24 Module Regulates Reproductive Development and Male Fertility in Citrus

MicroRNA399 (miR399) regulates phosphate homeostasis in plants by down-regulating the expression of PHOSPHATE2 (PHO2, or UBC24 encoding the ubiquitin-conjugating E2 enzyme). We previously identified CsmiR399a.1 in a small RNA sequencing screen of a male-sterile somatic cytoplasmic hybrid (or cybrid) of pummelo (Citrus grandis). Here, we report that miR399 affects reproductive development and male fertility in citrus. Down-regulation of CsmiR399a.1 using a short tandem target mimic (STTM) led to abnormal floral development, inhibition of anther dehiscence, and decreased pollen fertility. When grown in inorganic phosphate (Pi)-sufficient conditions, CsmiR399a.1-STTM plants had lower total phosphorus content in their leaves than the wild type and showed typical symptoms of Pi deficiency. In CsmiR399a.1-STTM plants, the expression of genes involved in starch metabolism and Pi homeostasis was significantly different than in the wild type. Thus, we conclude that miR399-STTM mimicked Pi deficiency, disturbed starch metabolism, and was responsible for pollen grain collapse in the transgenic lines. We identified CsUBC24, a citrus homolog of Arabidopsis (Arabidopsis thaliana) AtUBC24 (PHO2), as a target of CsmiR399a.1 that physically interacts with the floral development regulators SEPALLATA family (CsSEP1.1, CsSEP1.2, and CsSEP3) and the anther dehiscence regulator INDUCER OF CBF EXPRESSION1 (CsICE1). We hypothesize that CsUBC24 downregulates the CsSEPs, which disrupts the floral meristem identity regulatory network and leads to developmental abnormalities in flowers. By interacting with CsICE1, CsUBC24 disturbs stomate function on the anther surface, which inhibits anther dehiscence. These findings indicate that a miR399-based mechanism influences both reproductive development and male fertility in citrus.

Identification of key genes related to seedlessness by genome-wide detection of structural variation and transcriptome analysis in 'Shijiwuhe' pear

Seedless fruits are highly marketable because they are easier to eat than fruits with seeds. 'Shijiwuhe' is a seedless pear cultivar that is a mutant derived from an F1 hybridization population ('Bartlett' x 'Yali'). Little is known about the key genes controlling seedless pear fruit. In this study, field experiments revealed that seedless 'Shijiwuhe' pear was not due to parthenocarpy, and that it was self-incompatible. Single nucleotide polymorphisms (SNPs), small insertions and deletions (InDels) and structural variations (SVs) were characterized using DNA sequencing data between 'Shijiwuhe' and parental cultivars. A total of 1498 genes were found to be affected by SV and over 50% of SVs were located in promoter regions. Transcriptome analysis was conducted at three time points (4, 8, and 12 days after cross-pollination) during early fruit development of 'Shijiwuhe', 'Bartlett', and 'Yali'. In total, 1438 differentially expressed genes (DEGs) were found between 'Shijiwuhe' and parental cultivars 'Bartlett' and 'Yali'. We found 1193 SVs that caused differential expression of genes at 4 DACP. Among them, over 100 genes were in pathways related to seed nutrition and energy storage and 41 candidate genes encoded several important transcription factors, such as MYB, WRKY, NAC, and bHLH, which might play important roles in seed development. The qRT-PCR results also confirmed that the candidate genes with SVs showed differential expression between 'Shijiwuhe' pear and 'Bartlett' or 'Yali'. This study, which combined field experiments, SV detection, and transcriptome analysis might provide an effective way to predict the candidate genes regulating the seedless trait and important gene resources for genetic improvement of pear.

Gibberellins Play a Role in Regulating Tomato Fruit Ripening

Although exogenous applications of gibberellins (GAs) delay tomato ripening, the regulatory mechanisms of GAs in the process have never been well recognized. Here, we report that the concentration of endogenous GAs is declined before the increase of ethylene production in mature-green to breaker stage fruits. We further demonstrate that reductions in GA levels via overexpression of a GA catabolism gene SlGA2ox1 specifically in fruit tissues lead to early ripening. Consistently, we have also observed that application of a GA biosynthetic inhibitor, prohexadione-calcium, at the mature-green stage accelerates fruit ripening, while exogenous GA3 application delays the process. Furthermore, we demonstrate that ethylene biosynthetic gene expressions and ethylene production are activated prematurely in GA-deficient fruits but delayed/reduced in exogenous GA3-treated WT fruits. We also show that the GA deficiency-mediated activation of ethylene biosynthesis is due to the activation of the ripening regulator genes RIN, NOR and CNR. In conclusion, our results demonstrate that GAs play a negative role in tomato fruit ripening.

Identification and expression analysis of strigolactone biosynthetic and signaling genes reveal strigolactones are involved in fruit development of the woodland strawberry (Fragaria vesca)

BACKGROUND

The development and ripening of fresh fruits is an important trait for agricultural production and fundamental research. Almost all plant hormones participate in this process. Strigolactones (SLs) are a new class of plant hormones that regulate plant organ development and stress tolerance, but little is known about their roles in fruit development.

RESULTS

In this study, we identified SL biosynthetic and signaling genes in woodland strawberry, a typical non-climacteric fruit, and analyzed the expression patterns of these genes in different plant tissues and developing fruits. One D27, two MAX1, and one LBO gene were identified as involved in SL biosynthesis, and one D14, one D3, and two D53 genes as related to SL signaling. The proteins encoded by these genes had similar motifs as SL biosynthetic and signaling proteins in rice and Arabidopsis. The genes had different expression levels in the root, stem, leaf, and petiole of woodland strawberry. In addition, the expression of most SL biosynthetic genes was high in developing carpel, anther, and style, while that of SL signaling genes was high in carpel and style, but low in anther, suggesting active SL biosynthesis and signaling in the developing carpel and style. Notably, the expression of SL biosynthetic and signaling genes was significantly increased in the receptacle after pollination and decreased during receptacle development. Moreover, low or no expression of these genes was detected in ripening fruits.

CONCLUSIONS

Our results suggest that SLs play a role in the early stages of woodland strawberry fruit development. Our findings provide insight into the function of SLs and will facilitate further study of the regulation by SLs of fresh fruit development.

A Transcript and Metabolite Atlas of Blackcurrant Fruit Development Highlights Hormonal Regulation and Reveals the Role of Key Transcription Factors

Blackcurrant fruit collected at six stages of development were assessed for changes in gene expression using custom whole transcriptome microarrays and for variation in metabolite content using a combination of liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry. Principal components analysis demonstrated that fruit development could be clearly defined according to their transcript or metabolite profiles. During early developmental stages, metabolite profiles were dominated by amino acids and tannins, whilst transcript profiles were enriched in functions associated with cell division, anatomical structure morphogenesis and cell wall metabolism. During mid fruit development, fatty acids accumulated and transcript profiles were consistent with seed and embryo development. At the later stages, sugars and anthocyanins accumulated consistent with transcript profiles that were associated with secondary metabolism. Transcript data also indicated active signaling during later stages of fruit development. A targeted analysis of signaling networks revealed a dynamic activation and repression of almost 60 different transcripts encoding transcription factors across the course of fruit development, many of which have been demonstrated as pivotal to controlling such processes in other species. Transcripts associated with cytokinin and gibberellin were highly abundant at early fruit development, whilst those associated with ABA and ethylene tended to be more abundant at later stages. The data presented here provides an insight into fruit development in blackcurrant and provides a foundation for further work in the elucidation of the genetic basis of fruit quality.