Ovule Abortion Research Articles

Seed yield in red clover is associated with meiotic abnormalities and in tetraploid genotypes also with self-compatibility

Red clover (Trifolium pratense L.) is a major forage legume crop with diploid and tetraploid cultivars. Seed yield is an important trait in red clover, but the underlying reasons for low seed yield in individual genotypes are not well known. Here we investigated direct associations between seed yield and ovule abortion, male meiotic abnormalities, and pollen quality in well-characterized, diploid and tetraploid red clover genotypes with contrasting seed yields. Ovule development was studied after manual pollinations: in most genotypes, high rates of embryo abortion occurred between 7 and 14 days after pollination. However, the frequencies of developing, underdeveloped and shrivelled ovules were similar in diploid and tetraploid genotypes and were not associated with seed yield. Surprisingly, self-pollination only took place in tetraploid genotypes with high seed yield (83% self-pollination on average). The frequencies of meiotic abnormalities during microsporogenesis were investigated, in addition to pollen viability and pollen germination capacity. Tetraploid genotypes displayed more meiotic abnormalities (17.3% and 7.0% respectively) and lower pollen germination (39% and 63% respectively) than diploids. A negative trend was present between meiotic abnormalities and seed yield. In conclusion, our study reveals that high seed yield was associated with a low degree of abnormalities in male meiosis in diploid and tetraploid genotypes, and with the ability to self-pollinate in the tetraploid genotypes investigated. In certain genotypes, defective male meiosis may be a primary cause of low pollen quality and low seed yield.

Comparative development of staminate and pistillate flowers in the dioecious cactus Opuntia robusta.

PCD role in unisexual flowers. The developmental processes underlying the transition from hermaphroditism to unisexuality are key to understanding variation and evolution of floral structure and function. A detailed examination of the cytological and histological patterns involved in pollen and ovule development of staminate and pistillate flowers in the dioecious Opuntia robusta was undertaken, and the potential involvement of programmed cell death in the abortion of the sex whorls was explored. Flowers initiated development as hermaphrodites and became functionally unisexual by anthesis. Female individuals have pistillate flowers with a conspicuous stigma, functional ovary, collapsed stamens and no pollen grains. Male individuals have staminate flowers, with large yellow anthers, abundant pollen grains, underdeveloped stigma, style and an ovary that rarely produced ovules. In pistillate flowers, anther abortion resulted from the premature degradation of the tapetum by PCD, followed by irregular deposition of callose wall around the microsporocytes, and finally by microspore degradation. In staminate flowers, the stigma could support pollen germination; however, the ovaries were reduced, with evidence of placental arrest and ovule abortion through PCD, when ovules were present. We demonstrate that PCD is recruited in both pistillate and staminate flower development; however, it occurs at different times of floral development. This study contributes to the understanding of the nature of the O. robusta breeding system and identifies developmental landmarks that contribute to sexual determination in Cactaceae.

Mulching Affects Seed Set, Provisioning, and Offspring Performance of Vicia unijuga (Fabaceae)

Core Ideas Seed set of V. unijuga plants can be maximized by mulching in subalpine conditions. Plastic mulching increased seed provisioning, thus improving V. unijuga seed quality. Increased seed provisioning (mass) of V. unijuga improved germination success. Large seeds/seedlings have higher competitive ability relative to small seeds. ABSTRACTOur aim was to identify the soil and environmental modifications needed to improve seed set and seed quality of the perennial forage legume perennial vetch (Vicia unijuga A. Br.) in harsh subalpine conditions. A 3‐yr field experiment was conducted in a subalpine zone of China to evaluate the effects of modified soil temperature and moisture conditions generated by no mulching (control), plastic film mulching (FM), removal of plastic film mulching at the 30% flowering stage (RM), and threshed barley straw mulching (SM) on seed set, mass, reserves, germination, and seedling growth. The FM and SM treatments were efficient in increasing seed maturation and decreasing ovule abortion at the base of the pods. There were higher 100‐seed weight (HSW) and seed nutrient reserves in the FM and RM treatments, accompanied by higher final germination percentage (FGP) and lower time to 50% germination (T50) and greater initial seedling growth than in the control, whereas the reverse was true for the SM treatment. Modified soil temperature and moisture generated by mulching improved offspring performance traits of V. unijuga through an increase in HSW. The HSW was positively correlated with FGP and seedling growth traits and was negatively associated with T50. In conclusion, the FM treatment provided adequate soil temperature and water resources to maximize seed set by V. unijuga plants. The well‐provisioned seeds from this treatment conferred the advantages of good offspring performance on high germination and seedling growth traits.

Reproductive potential of the functionally female native Croatian grapevine 'Grk bijeli'

A native Croatian grapevine 'Grk bijeli', sharing a parent-offspring relationships with 'Tribidrag' (aka 'Zinfandel'), is grown exclusively on the Adriatic island of Korcula. It is one of the grape cultivars with female-only functional flowers, causing reduced fertilisation and leads to problems in grape production and wine quality. A typical cluster of 'Grk bijeli' at maturity contains fully developed seeded berries, in addition to a highly variable proportion of undersized seedless berries. The aim of this study was to identify the cause of the reduced reproduction potential of 'Grk bijeli' in order to establish a better growing environment for improved yield and grape quality. 'Grk bijeli' female gametophyte develops normaly and at maturity contains both egg and central cell, together with two synergid cells and three antipodal cells. On the other hand, 'Grk bijeli' pollen grains show developmental deviations. Specifically, most of the pollen grains undergo the first pollen mitosis and contain one vegetative cell and one generative cell, while 20 % of ungerminating grains also accomplish the second pollen mitosis, giving rise to two sperm cells and one vegetative cell. Morover, 'Grk bijeli' pollen has acolporate morphology, which prevents germination and contributes to reduced reproduction. Furthermore, fertilisation after pollination with other varieties results in various degrees of ovule abortion depending on the pollinator, revealing Croatian cultivars 'Plavac mali crni' and 'Posip bijeli' as favourable varieties. Although this study describes a highly valuable cultivar of local importance, it also contributes to fundamental knowledge of grapevine reproductive biology and offers a strategy for improvement of wine production and oenological performance of semi-fertile varieties in general.

Genome-wide identification and expression analysis reveal the potential function of ethylene responsive factor gene family in response to Botrytis cinerea infection and ovule development in grapes (Vitis vinifera L.).

The prevention of Botrytis cinerea infection and the study of grape seedlessness are very important for grape industries. Finding correlated regulatory genes is an important approach towards understanding their molecular mechanisms. Ethylene responsive factor (ERF) gene family play critical roles in defence networks and the growth of plants. To date, no large-scale study of the ERF proteins associated with pathogen defence and ovule development has been performed in grape (Vitis vinifera L.). In the present study, we identified 113 ERF genes (VvERF) and named them based on their chromosome locations. The ERF genes could be divided into 11 groups based on a multiple sequence alignment and a phylogenetic comparison with homologues from Arabidopsis thaliana. Synteny analysis and Ka/Ks ratio calculation suggested that segmental and tandem duplications contributed to the expansion of the ERF gene family. The evolutionary relationships between the VvERF genes were investigated by exon-intron structure characterisation, and an analysis of the cis-acting regulatory elements in their promoters suggested potential regulation after stress or hormone treatments. Expression profiling after infection with the fungus, B. cinerea, indicated that ERF genes function in responses to pathogen attack. In addition, the expression levels of most ERF genes were much higher during ovule development in seedless grapes, suggesting a role in ovule abortion related to seedlessness. Taken together, these results indicate that VvERF proteins are involved in responses to Botrytis cinerea infection and in grape ovule development. This information may help guide strategies to improve grape production.

Genome-wide Identification, Phylogenetic Analysis, and Expression Profiling of CONSTANS-like (COL) Genes in Vitis vinifera

The CONSTANS (CO) gene plays an important role in the flowering of plants. However, the other precise roles of the CO gene are poorly understood. We carried out a genomic census and analysis of expression patterns for CONSTANS-like genes in Vitis vinifera (VviCOLs) to reveal the molecular characteristics of VviCOLs. Twelve VviCOLs were identified and 11 of their full-length complementary DNAs were cloned. Multiple sequence alignment suggested the VviCOLs contained B-box and CCT conserved domains. We further classified the VviCOLs into three groups according to the variability of the second B-box domain. Synteny analysis showed that eight orthologous gene pairs were identified between grapevine and Arabidopsis, suggesting that eight pairs may descend from a common evolutionary ancestor. Tissue expression analysis of COL genes in cv. Pinot Noir showed VviCOL11a and VviCOL11b were specifically expressed in flower bud, whereas VviCOL16b was only expressed in leaves. Ten VviCOLs were expressed in the developing ovule and six of them showed higher expression in the ovule of cv. Thompson Seedless than that of cv. Pinot Noir, indicating that VviCOLs were involved in the process of seed development or ovule abortion. Furthermore, nine of twelve VviCOLs were expressed in cv. Pinot Noir leaves and all of these nine genes had a response to exogenous hormone application. In summary, our findings provide a new insight into the further studies of VviCOLs, especially in terms of seed development and hormone response.

Ovary abortion is prevalent in diverse maize inbred lines and is under genetic control

Crop improvement programs focus on characteristics that are important for plant productivity. Typically genes underlying these traits are identified and stacked to create improved cultivars. Hence, identification of valuable traits for plant productivity is critical for plant improvement. Here we describe an important characteristic for maize productivity. Despite the fact mature maize ears are typically covered with kernels, we find that only a fraction of ovaries give rise to mature kernels. Non-developed ovaries degenerate while neighboring fertilized ovaries produce kernels that fill the ear. Abortion occurs throughout the ear, not just at the tip. We show that the fraction of aborted ovaries/kernels is genetically controlled and varies widely among maize lines, and low abortion genotypes are rare. Reducing or eliminating ovary abortion could substantially increase yield, making this characteristic a new target for selection in maize improvement programs.

Gene cloning and expression analyses of WBC genes in the developing grapevine seeds

White-brown complex (WBC) transporters, also called half-size ATP binding cassette G (ABCG) transporters, are involved in many biological processes, including seed development; however, the WBC transporters in grapevines received less attention to date. To reveal the molecular characteristics of WBCs and the connection between WBCs and agronomic traits of stenospermocarpic (seedless) grapevine, we carried out a genomic census and analysis of ovule-associated expression for VvWBC genes in grapevine. We identified 30 VvWBC genes and cloned full-length complementary DNAs (cDNAs) for 20 of these. The tissue or organ-specific expression analysis showed that several VvWBCs exhibited distinct expression patterns with some showing tissue specificity. Twelve VvWBC genes were found to be expressed in the developing ovules. Moreover, the results of quantitative real-time PCR (qRT-PCR) suggested that four of twelve ovule-expressed VvWBCs have distinct expression profiles during the development of ovules between seeded and stenospermocarpic grapevines. These four genes might be involved in ovule abortion. Meanwhile, chromosome mapping, multiple sequence alignments, exon/intron structure analyses and synteny analyses were preformed on VvWBC genes. Our experiments provide a new perspective on the mechanism of stenospermocarpic seedlessness and put forward a framework for further study of WBC transporters.

Identification of genes regulating ovary differentiation after pollination in hazel by comparative transcriptome analysis

BackgroundHazel (Corylus spp.) exhibits ovary differentiation and development that is initiated from the ovary primordium after pollination, conferring the plant with a unique delayed fertilization. Failure of development of the ovary and ovule after pollination can lead to ovary abortion and blank fruit formation, respectively, with consequent yield loss. However, the genes involved in ovary and ovule differentiation and development are largely unknown.ResultsIn unpollinated pistillate inflorescences (stage F), the stigma shows an extension growth pattern. After pollination, a rudimentary ovary begins to form (stage S), followed by ovule differentiation (stage T) and growth (stage FO). Total RNA was obtained from pistillate inflorescences or young ovaries at stage F, S, T and FO, and sequencing was carried out on a HiSeq 4000 system. De novo assembly of sequencing data yielded 62.58 Gb of nucleotides and 90,726 unigenes; 5524, 3468, and 8714 differentially expressed transcripts were identified in F-vs-S, S-vs-T, and T-vs-FO paired comparisons, respectively. An analysis of F-vs-S, S-vs-T, and T-vs-FO paired comparisons based on annotations in the Kyoto Encyclopedia of Genes and Genomes revealed six pathways that were significantly enriched during ovary differentiation, including ko04075 (Plant hormone signal transduction). Auxin level increased after pollination, and an immunohistochemical analysis indicated that auxin was enriched at the growth center of pistillate inflorescences and young ovaries. These results indicate that genes related to auxin biosynthesis, transport, signaling, the floral quartet model, and flower development may regulate ovary and ovule differentiation and development in hazel.ConclusionsOur findings provide insight into the molecular mechanisms of ovary differentiation and development after pollination in this economically valuable plant.

Embryology of Mammillaria dioica (Cactaceae) reveals a new male sterility phenotype

Although most of angiosperms have bisexual flowers, unisexuality has evolved in different angiosperms lineages. Bisexual flowers have been reported for the majority of species in Cactaceae; however, three of four subfamilies have members with unisexual flowers. Mammillaria dioica (Cactoideae) has been reported having unisexual flowers in gynodioecious, dioecious or trioecious breeding systems. However, a developmental study is missing to clarify the breeding system and the anther or ovule abortion process. This study describes breeding system and embryology of M. dioica from a population at Baja California Sur, México, through the careful examination of floral morphology and by using light and scanning electron microscopy at different stages of floral development. Hermaphrodite and female individuals were identified in the population with a ratio of 67.5% and 32.5% respectively. In pistillate and bisexual flowers, the ovary presents many campylotropous, bitegmic and crassinucellate ovules with well-formed style and stigma, likewise both morphs produce fruits and seeds. Moreover, in bisexual flowers, stamens are well-developed and contain pollen grains, anther wall development is of the monocotyledonous type, the microspore tetrads are tetrahedral, and mature pollen grain is three-celled with reticulate exine and tricolpate. In pistillate flowers, the anthers develop just before the meiosis of the microspore mother cells, and are collapsed at anthesis; the tapetum is bi-layered and exhibits abnormal growth, each cell is uninucleate in both layers. The inner layer of tapetum develops fibrous reticulate cell wall thickenings, while endothecium develops U-shapes cell wall thickenings. No tapetal secretory layer was observed, which means a fail to support the development of microspore mother cells. This male sterility phenotype has not been reported for other species of Cactaceae with unisexual flowers neither flowering plants.

New insight into ovary abortion during ovary development of hazelnut through a combined proteomic and transcriptomic analysis

Abstract Hazel (Corylus spp.) is the most economically important species in the Betulaceae family. Frequent ovary abortion during the prefertilization stage causes the high drop ratio of pistillate flowers and smaller fruit numbers in a fruit cluster, resulting in yield loss. To better understand the mechanism of ovary abortion formation in hazel, we conducted transcriptomic and proteomic analyses and identified genes and proteins that were altered in response to ovary abortion. A total of 89,846 unigenes and 4343 proteins were identified using RNA-seq and iTRAQ technology, respectively. Among them, 1895 unigenes and 710 proteins were differentially expressed and accumulated in the developing and abortive ovary respectively. Furthermore, we employed the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, revealing pathways that are significantly enriched in both transcriptomic and proteomic assays. These include the phenylalanine metabolic pathway, biosynthesis of phenylpropanoid, biosynthesis of secondary metabolites, and ascorbate and aldarate metabolism. Transcriptome-proteome integrative analysis revealed 42 correlations. Among these, 32 correlations with same changing trend (that are involved in metabolism stress response, vascular strand development, water transport, and seed development) are likely associated with abortive ovary formation. Importantly, ethylene (ETH), jasmonic acid (JA), and salicylic acid (SA) signal transduction pathways may contribute to the regulation of the abortive ovary formation via the up-regulation of ethylene-responsive transcription factor 1 (ERF1/2), jasmonate ZIM domain-containing protein (JAZ), transcription factor MYC2 (MYC2), transcription factor (TGA), and pathogenesis-related protein 1(PR-1). Our work will facilitate the identification of ovary abortion related genes and proteins and provide insights into the molecular mechanism of fruit development.

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Genome-wide identification and expression analyses of the homeobox transcription factor family during ovule development in seedless and seeded grapes

Seedless grapes are of considerable importance for the raisin and table grape industries. Previous transcriptome analyses of seed development in grape revealed that genes encoding homeobox transcription factors were differentially regulated in seedless compared with seeded grape during seed development. In the present study, we identified a total of 73 homeobox-like genes in the grapevine genome and analyzed the genomic content and expression profiles of these genes. Based on domain architecture and phylogenetic analyses grape homeobox genes can be classified into eleven subfamilies. An analysis of the exon-intron structures and conserved motifs provided further insight into the evolutionary relationships between these genes. Evaluation of synteny indicated that segmental and tandem duplications have contributed greatly to the expansion of the grape homeobox gene superfamily. Synteny analysis between the grape and Arabidopsis genomes provided a potential functional relevance for these genes. The tissue-specific expression patterns of homeobox genes suggested roles in both vegetative and reproductive tissues. Expression profiling of these genes during the course of ovule development in seeded and seedless cultivars suggested a potential role in ovule abortion associated with seedlessness. This study will facilitate the functional analysis of these genes and provide new resources for molecular breeding of seedless grapes.

Evolution and expression analysis reveal the potential role of the HD-Zip gene family in regulation of embryo abortion in grapes (Vitis vinifera L.)

BackgroundThe HD-Zip family has a diversity of functions during plant development. In this study, we identify 33 HD-Zip transcription factors in grape and detect their expressions in ovules and somatic embryos, as well as in various vegetative organs.ResultsA genome-wide survey for HD-Zip transcription factors in Vitis was conducted based on the 12 X grape genome (V. vinifera L.). A total of 33 members were identified and classified into four subfamilies (I-IV) based on phylogeny analysis with Arabidopsis, rice and maize. VvHDZs in the same subfamily have similar protein motifs and intron/exon structures. An evaluation of duplication events suggests several HD-Zip genes arose before the divergence of the grape and Arabidopsis lineages. The 33 members of HD-Zip were differentially expressed in ovules of the stenospermic grape, Thompson Seedless and of the seeded grape, Pinot noir. Most have higher expressions during ovule abortion in Thompson Seedless. In addition, transcripts of the HD-Zip family were also detected in somatic embryogenesis of Thompson Seedless and in different vegetative organs of Thompson Seedless at varying levels. Additionally, VvHDZ28 is located in the nucleus and had transcriptional activity consistent with the typical features of the HD-Zip family. Our results provide a foundation for future grape HD-Zip gene function research.ConclusionsThe identification and expression profiles of the HD-Zip transcription factors in grape, reveal their diverse roles during ovule abortion and organ development. Our results lay a foundation for functional analysis of grape HDZ genes.

Differential proteomic analysis revealing the ovule abortion in the female-sterile line of Pinus tabulaeformis Carr.

Ovule abortion affects the yield and quality of Pinus tabulaeformis Carr. seeds. Research into ovule abortion has importance for improving the seed setting rate and establishing artificial seed production techniques. Fertile line (FL) ovules (FL-E) and sterile line (SL) ovules (SL-E) in the early stage of free nuclear mitosis of megagametophyte (FNMM), FL ovules (FL-L) and SL ovules (SL-L) in the late stage of FNMM of P. tabulaeformis were collected as materials. 4192 proteins were identified by isobaric tags for relative and absolute quantitation (iTRAQ)-based analysis. Bioinformatics analysis implied that in SL ovules, substances and energy might be deficient, perhaps leading to abnormal DNA replication. Because the incomplete antioxidant system and the abnormal expression levels of enzymes involved in cell signal transduction, DNA DSBs probably occurs. Facing the abnormities of DNA replication and damage, the cell cycle was arrested and the DNA damage failed to be repaired, potentially resulting in the occurrence of PCD. Taken together, an inference can be drawn from our study – substance and energy deficiencies, reactive oxygen stress, and the failure of both cell cycle progression and DNA damage repair, which possibly hinder FNMM, leading to ovule abortion in the female-sterile line of P. tabulaeformis.

Comparison of phytohormone biosynthesis and signal transduction pathways in developing and abortive hazelnut ovules

In hazelnuts, ovule abortion is associated with the formation of empty nuts, resulting in serious yield losses. Phytohormones play important roles in plant growth and development; however, the mechanisms through which they regulate ovule abortion in hazelnut are largely unknown. RNA-seq identified 1209 differentially expressed genes with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation between developing and abortive ovules in hazelnut. Hormone signal transduction (ko04075), and several phytohormone biosynthesis pathways, were found to be significantly enriched after pathway enrichment analysis. Compared with developing ovules, the levels of indole-3-acetic acid (IAA), gibberellins (GA), cytokinin (CTK), and salicylic acid (SA) were found to be significantly lower in abortive ovules, while levels of abscisic acid (ABA), ethylene (ETH), and jasmonic acid (JA) were found to be significantly higher. Consistent with these results, some important rate-limiting enzymes involved in the biosynthesis of phytohormones, including 9-cis-epoxycarotenoid dioxygenase, ACC synthase, and phospholipase A1 were significantly up-regulated in abortive ovules. Some key genes in the ETH, JA, and ABA signal transduction pathways were highly upregulated, including ethylene-responsive transcription factor 1 (ERF1/2) and the serine/threonine-protein kinase CTR1 in the ETH signal pathway, jasmonate ZIM domain-containing protein (JAZ) and the transcription factor MYC2 in the JA signal pathway, and ABA responsive element binding factor (ABF) in the JA signal pathway. Thus, ABA, ETH, and JA signaling were more active in abortive ovules than in developing ovules. Expression levels of NCED, ABF, ACS, ERF1/2, PLA1, and MYC2 revealed by q-RT-PCR were consistent with the results obtained by differentially expressed genes (DEG) analysis. Our data suggest that multiple phytohormone signaling pathways are involved in the development of hazelnut ovules. Inhibition of IAA, GA, CTK, and SA biosynthesis and signaling pathways, and activation of ABA, ETH, and JA biosynthesis and signaling pathways may contribute to the formation of abortive ovules in hazelnut.

Seed size plasticity in response to embryonic lethality conferred by ectopic CYCD activation is dependent on plant architecture

ABSTRACTThe size of seeds is the result of cell proliferation and growth in the three seed compartments: the embryo, endosperm and integuments. Targeting expression of the D-type cyclin CYCD7;1 to the central cell and early endosperm (FWA:CYCD7;1) triggered nuclear divisions and partial ovule abortion, reducing seed number in each silique and leading to increased seed size. A similar effect on seed size was observed with other segregating embryo lethal mutations, suggesting caution is needed in interpreting apparent seed size phenotypes. Here, we show that the positive effect of FWA:CYCD7;1 on Arabidopsis seed size is modulated by the architecture of the mother plant. Larger seeds were produced in FWA:CYCD7;1 lines with unmodified inflorescences, and also upon removal of side branches and axillary stems. This phenotype was absent from inflorescences with increased axillary floral stems produced by pruning of the main stem. Given this apparent confounding influence of resource allocation on transgenes effect, we conclude that plant architecture is a further important factor to consider in appraising seed phenotypes.

Is Change in Ovary Carbon Status a Cause or a Consequence of Maize Ovary Abortion in Water Deficit during Flowering?

Flower or grain abortion causes large yield losses under water deficit. In maize (Zea mays), it is often attributed to a carbon limitation via the disruption of sucrose cleavage by cell wall invertases in developing ovaries. We have tested this hypothesis versus another linked to the expansive growth of ovaries and silks. We have measured, in silks and ovaries of well-watered or moderately droughted plants, the transcript abundances of genes involved in either tissue expansion or sugar metabolism, together with the concentrations and amounts of sugars, and with the activities of major enzymes of carbon metabolism. Photosynthesis and indicators of sugar export, measured during water deprivation, suggested sugar export maintained by the leaf. The first molecular changes occurred in silks rather than in ovaries and involved genes affecting expansive growth rather than sugar metabolism. Changes in the concentrations and amounts of sugars and in the activities of enzymes of sugar metabolism occurred in apical ovaries that eventually aborted, but probably after the switch to abortion of these ovaries. Hence, we propose that, under moderate water deficits corresponding to most European drought scenarios, changes in carbon metabolism during flowering time are a consequence rather than a cause of the beginning of ovary abortion. A carbon-driven ovary abortion may occur later in the cycle in the case of carbon shortage or under very severe water deficits. These findings support the view that, until the end of silking, expansive growth of reproductive organs is the primary event leading to abortion, rather than a disruption of carbon metabolism.

Transcript Analysis and Regulative Events during Flower Development in Olive (Olea europaea L.).

The identification and characterization of transcripts involved in flower organ development, plant reproduction and metabolism represent key steps in plant phenotypic and physiological pathways, and may generate high-quality transcript variants useful for the development of functional markers. This study was aimed at obtaining an extensive characterization of the olive flower transcripts, by providing sound information on the candidate MADS-box genes related to the ABC model of flower development and on the putative genetic and molecular determinants of ovary abortion and pollen-pistil interaction. The overall sequence data, obtained by pyrosequencing of four cDNA libraries from flowers at different developmental stages of three olive varieties with distinct reproductive features (Leccino, Frantoio and Dolce Agogia), included approximately 465,000 ESTs, which gave rise to more than 14,600 contigs and approximately 92,000 singletons. As many as 56,700 unigenes were successfully annotated and provided gene ontology insights into the structural organization and putative molecular function of sequenced transcripts and deduced proteins in the context of their corresponding biological processes. Differentially expressed genes with potential regulatory roles in biosynthetic pathways and metabolic networks during flower development were identified. The gene expression studies allowed us to select the candidate genes that play well-known molecular functions in a number of biosynthetic pathways and specific biological processes that affect olive reproduction. A sound understanding of gene functions and regulatory networks that characterize the olive flower is provided.

Genetic architecture and mechanism of seed number per pod in rapeseed: elucidated through linkage and near-isogenic line analysis.

Seed number per pod (SNPP) is one of the major yield components and breeding targets in rapeseed that shows great variation and is invaluable for genetic improvement. To elucidate the genetic architecture and uncover the mechanism of SNPP, we identified five quantitative trait loci (QTLs) using the BnaZNRIL population, which were integrated with those of previous studies by physical map to demonstrate a complex and relatively complete genetic architecture of SNPP. A major QTL, qSN.A6, was successfully fine-mapped from 1910 to 267 kb using near-isogenic line (NIL). In addition, qSN.A6 exhibited an antagonistic pleiotropy on seed weight (SW), which is caused by a physiological interaction in which SNPP acts “upstream” of SW. Because the negative effect of qSN.A6 on SW cannot fully counteract its positive effect on SNPP, it also enhanced the final yield (17.4%), indicating its great potential for utilization in breeding. The following genetic and cytological experiments further confirmed that the different rate of ovule abortion was responsible for the ~5 seed difference between Zhongshuang11 and NIL-qSN.A6. This systematic approach to dissecting the comprehensive genetic architecture of SNPP and characterizing the underlying mechanism has advanced the understanding of SNPP and will facilitate the development of high-yield cultivars.