Regulation of nucellar embryony, a mode of sporophytic apomixis in Citrus resembling somatic embryogenesis.

Apomixis, is an asexual mode of seed formation resulting in genetically identical or clonal seed with a maternal genotype. Apomixis has not been reported in seed crops where its flexible application in plant breeding could accelerate delivery of new varieties. By contrast, a sporophytic form of apomixis termed nucellar or adventitious embryony is common in the Rutaceae containing Citrus crop species.

Phenotypic plasticity of aposporous embryo sac development in .

Apomixis in follows a developmental pathway of apospory, where an unreduced embryo sac develops from a somatic ovule cell without meiosis. The avoidance of meiosis together with fertilization-independent seed formation leads to clonal progeny genetically identical to the maternal plant. We have previously described the initial developmental steps of aposporous embryo sac formation in and here, we cytologically observed more than 500 ovules with a focus on the later stages of embryo sac maturation.

Asexual Female Gametogenesis Involves Contact with a Sexually-Fated Megaspore in Apomictic .

Apomixis results in asexual seed formation where progeny are identical to the maternal plant. In ovules of apomictic species of the subgenus , meiosis of the megaspore mother cell generates four megaspores. Aposporous initial (AI) cells form during meiosis in most ovules.

Generation of an integrated Hieracium genomic and transcriptomic resource enables exploration of small RNA pathways during apomixis initiation.

Background: Application of apomixis, or asexual seed formation, in crop breeding would allow rapid fixation of complex traits, economizing improved crop delivery. Identification of apomixis genes is confounded by the polyploid nature, high genome complexity and lack of genomic sequence integration with reproductive tissue transcriptomes in most apomicts.

Results: A genomic and transcriptomic resource was developed for Hieracium subgenus Pilosella (Asteraceae) which incorporates characterized sexual, apomictic and mutant apomict plants exhibiting reversion to sexual reproduction.

New observations on gametogenic development and reproductive experimental tools to support seed yield improvement in cowpea [Vigna unguiculata (L.) Walp].

Cowpea reproductive tools. Vigna unguiculata L. Walp.

A Comparison of In Vitro and In Vivo Asexual Embryogenesis.

In plants, embryogenesis generally occurs through the sexual process of double fertilization, which involves a haploid sperm cell fusing with a haploid egg cell to ultimately give rise to a diploid embryo. Embryogenesis can also occur asexually in the absence of fertilization, both in vitro and in vivo. Somatic or gametic cells are able to differentiate into embryos in vitro following the application of plant growth regulators or stress treatments.

Developmentally regulated HEART STOPPER, a mitochondrially targeted L18 ribosomal protein gene, is required for cell division, differentiation, and seed development in Arabidopsis.

Evidence is presented for the role of a mitochondrial ribosomal (mitoribosomal) L18 protein in cell division, differentiation, and seed development after the characterization of a recessive mutant, heart stopper (hes). The hes mutant produced uncellularized endosperm and embryos arrested at the late globular stage. The mutant embryos differentiated partially on rescue medium with some forming callus.

A reference genetic linkage map of apomictic Hieracium species based on expressed markers derived from developing ovule transcripts.

Background And Aims: Apomixis in plants generates clonal progeny with a maternal genotype through asexual seed formation. Hieracium subgenus Pilosella (Asteraceae) contains polyploid, highly heterozygous apomictic and sexual species. Within apomictic Hieracium, dominant genetic loci independently regulate the qualitative developmental components of apomixis.

Expression patterns and protein structure of a lipid transfer protein END1 from Arabidopsis.

Arabidopsis END1-LIKE (AtEND1) was identified as a homolog of the barley endosperm-specific gene END1 and provides a model for the study of this class of genes and their products. The END1 is expressed in the endosperm transfer cells (ETC) of grasses. The ETC are responsible for transfer of nutrients from maternal tissues to the developing endosperm.

The genetic control of apomixis: asexual seed formation.

Apomixis (asexual seed formation) is the result of a plant gaining the ability to bypass the most fundamental aspects of sexual reproduction: meiosis and fertilization. Without the need for male fertilization, the resulting seed germinates a plant that develops as a maternal clone. This dramatic shift in reproductive process has been documented in many flowering plant species, although no major seed crops have been shown to be capable of apomixis.

Imprinting in rice: the role of DNA and histone methylation in modulating parent-of-origin specific expression and determining transcript start sites.

Over 200 imprinted genes in rice endosperm are known, but the mechanisms modulating their parental allele-specific expression are poorly understood. Here we use three imprinted genes, OsYUCCA11, yellow2-like and ubiquitin hydrolase, to show that differential DNA methylation and tri-methylation of histone H3 lysine 27 (H3K27me3 ) in the promoter and/or gene body influences allele-specific expression or the site of transcript initiation. Paternal expression of OsYUCCA11 required DNA methylation in the gene body whereas the gene body of the silenced maternal allele was hypomethylated and marked with H3K27me3 .

Traffic monitors at the cell periphery: the role of cell walls during early female reproductive cell differentiation in plants.

The formation of female gametes in plants occurs within the ovule, a floral organ that is also the precursor of the seed. Unlike animals, plants lack a typical germline separated from the soma early in development and rely on positional signals, including phytohormones, mobile mRNAs and sRNAs, to direct diploid somatic precursor cells onto a reproductive program. In addition, signals moving between plant cells must overcome the architectural limitations of a cell wall which surrounds the plasma membrane.

Enlarging cells initiating apomixis in Hieracium praealtum transition to an embryo sac program prior to entering mitosis.

Hieracium praealtum forms seeds asexually by apomixis. During ovule development, sexual reproduction initiates with megaspore mother cell entry into meiosis and formation of a tetrad of haploid megaspores. The sexual pathway ceases when a diploid aposporous initial (AI) cell differentiates, enlarges, and undergoes mitosis, forming an aposporous embryo sac that displaces sexual structures.

Genetic separation of autonomous endosperm formation (AutE) from the two other components of apomixis in Hieracium.

In apomictic Hieracium subgenus Pilosella species, embryo sacs develop in ovules without meiosis. Embryo and endosperm formation then occur without fertilization, producing seeds with a maternal genotype encased in a fruit (achene). Genetic analyses in H.

Somatic small RNA pathways promote the mitotic events of megagametogenesis during female reproductive development in Arabidopsis.

Female gamete development in Arabidopsis ovules comprises two phases. During megasporogenesis, a somatic ovule cell differentiates into a megaspore mother cell and undergoes meiosis to produce four haploid megaspores, three of which degrade. The surviving functional megaspore participates in megagametogenesis, undergoing syncytial mitosis and cellular differentiation to produce a multicellular female gametophyte containing the egg and central cell, progenitors of the embryo and endosperm of the seed.

Sporophytic ovule tissues modulate the initiation and progression of apomixis in Hieracium.

Apomixis in Hieracium subgenus Pilosella initiates in ovules when sporophytic cells termed aposporous initial (AI) cells enlarge near sexual cells undergoing meiosis. AI cells displace the sexual structures and divide by mitosis to form unreduced embryo sac(s) without meiosis (apomeiosis) that initiate fertilization-independent embryo and endosperm development. In some Hieracium subgenus Pilosella species, these events are controlled by the dominant LOSS OF APOMEIOSIS (LOA) and LOSS OF PARTHENOGENESIS (LOP) loci.

The female gametophyte.

The angiosperm female gametophyte is critical for plant reproduction. It contains the egg cell and central cell that become fertilized and give rise to the embryo and endosperm of the seed, respectively. Female gametophyte development begins early in ovule development with the formation of a diploid megaspore mother cell that undergoes meiosis.

Chromosomes carrying meiotic avoidance loci in three apomictic eudicot Hieracium subgenus Pilosella species share structural features with two monocot apomicts.

The LOSS OF APOMEIOSIS (LOA) locus is one of two dominant loci known to control apomixis in the eudicot Hieracium praealtum. LOA stimulates the differentiation of somatic aposporous initial cells after the initiation of meiosis in ovules. Aposporous initial cells undergo nuclear proliferation close to sexual megaspores, forming unreduced aposporous embryo sacs, and the sexual program ceases.

Molecular cloning and characterization of a linalool synthase from lemon myrtle.

Using a homology-based PCR strategy, we identified a cDNA with sequence similarity to linalool synthase from lemon myrtle. Functional expression of the cDNA (designated BcLS) gene in Escherichia coli yielded an active enzyme capable of catalyzing the conversion of geranyl diphosphate to (-)-linalool, i.e.

Crystallization and preliminary X-ray analysis of geraniol dehydrogenase from Backhousia citriodora (lemon myrtle).

A recombinant form of geraniol dehydrogenase (EC 1.1.1.

Sexual reproduction is the default mode in apomictic Hieracium subgenus Pilosella, in which two dominant loci function to enable apomixis.

Asexual seed formation, or apomixis, in the Hieracium subgenus Pilosella is controlled by two dominant independent genetic loci, LOSS OF APOMEIOSIS (LOA) and LOSS OF PARTHENOGENESIS (LOP). We examined apomixis mutants that had lost function in one or both loci to establish their developmental roles during seed formation. In apomicts, sexual reproduction is initiated first.

Apomixis in hawkweed: Mendel's experimental nemesis.

Mendel used hawkweeds and other plants to verify the laws of inheritance he discovered using Pisum. Trait segregation was not evident in hawkweeds because many form seeds asexually by apomixis. Meiosis does not occur during female gametophyte formation and the mitotically formed embryo sacs do not require fertilization for seed development.

Polycomb group gene function in sexual and asexual seed development in angiosperms.

In sexually reproducing angiosperms, double fertilization initiates seed development, giving rise to two fertilization products, the embryo and the endosperm. In the endosperm, a terminal nutritive tissue that supports embryo growth, certain genes are expressed differentially depending on their parental origin, and this genomic imbalance is required for proper seed formation. This parent-of-origin effect on gene expression, called genomic imprinting, is controlled epigenetically through histone modifications and DNA methylation.

The Arabidopsis MYB5 transcription factor regulates mucilage synthesis, seed coat development, and trichome morphogenesis.

The Arabidopsis thaliana MYB5 gene is expressed in trichomes and seeds, including the seed coat. Constitutive expression of MYB5 resulted in the formation of more small trichomes and ectopic trichomes and a reduction in total leaf trichome numbers and branching. A myb5 mutant displayed minimal changes in trichome morphology, while a myb23 mutant produced increased numbers of small trichomes and two-branched trichomes.