Sexual Plant Reproduction

Hybrid (oat×maize) zygotes developed into euhaploid plants with complete oat chromosome complements without maize chromosomes and into aneuhaploid plants with complete oat chromosome complements and different numbers of retained individual maize chromosomes. The elimination of maize chromosomes in the hybrid embryo is caused by uniparental genome loss during early steps of embryogenesis. Some of these haploid plants set seed in up to 50% of their self-pollinated spikelets. The high fertility was found to be mainly caused by formation of numerically unreduced female and male gametes (nunreduced=3x+0…3=21…24 chromosomes)...

The co-occurrence of apomixis (asexual reproduction) and polyploidy in plants has been the subject of debate in regard to the origin and evolution of asexuality. In recent years, polyploidy has been postulated as a maintenance and stabilization factor rather than as a source of apomixis origin. It is assumed polyploidy facilitates the compensation for mutation accumulation, and hence, the rare occurrence of diploid apomixis indirectly supports this finding. Nevertheless, diploid apomicts exist and are successful, especially in the genus Boechera...

We isolated protoplasts from male and female gametophytes of a strictly dioecious strain of the coenocytic marine green alga Bryopsis plumosa. The protoplasts successfully developed into macrothalli. These in turn produced swimming cells, which appeared similar to biflagellated gametes even when the mixed protoplasts were comprised of protoplasm from male and female gametophytes. We found that swimming cell sizes depended on the male/female protoplasm ratio; macrothalli successfully produced swimming cells with male/female protoplasm ratios of 10:0; 9:1; 7:3; 5:5; 1:9; and 0:10...

The development of the egg and canal cells in the fern Osmunda japonica Thunb. was studied during oogenesis by transmission electron microscopy. The mature egg possesses no fertilization pore and no typical egg envelope. In addition, an extra wall formed around the canal cells during oogenesis and apparently blocked protoplasmic connections between the egg and the canal cells. The periodic acid Schiff (PAS) reaction revealed that the extra wall was most likely composed of polysaccharides. Maturation of the egg was accompanied by the formation of a separation cavity above the egg and by some changes in the morphology of the nucleus and cytoplasmic organelles...

Male gametophyte development leading to the formation of a mature pollen grain is precisely controlled at various levels, including transcriptional, post-transcriptional and post-translational, during its whole progression. Transcriptomic studies exploiting genome-wide microarray technologies revealed the uniqueness of pollen transcriptome and the dynamics of early and late successive global gene expression programs. However, the knowledge of transcription regulation is still very limited. In this study, we focused on the identification of pollen-expressed transcription factor (TF) genes involved in the regulation of male gametophyte development...

Sexual plant reproduction requires multiple pollen-pistil interactions from the stigma (pollen adhesion, hydration, and germination) to the ovary (fertilization). Understanding the factors that regulate pollen tube growth is critical to understanding the processes essential to sexual reproduction. Many pollen tube growth assays (PTGAs) have shorter and slower pollen tube growth when compared to pollen tube growth through the style. The identification and study of factors that regulate pollen tube growth have been impeded by a lack of an efficient and reproducible PTGA...

Agave tequilana is a monocarpic perennial species that flowers after 5-8 years of vegetative growth signaling the end of the plant's life cycle. When fertilization is unsuccessful, vegetative bulbils are induced on the umbels of the inflorescence near the bracteoles from newly formed meristems. Although the regulation of inflorescence and flower development has been described in detail for monocarpic annuals and polycarpic species, little is known at the molecular level for these processes in monocarpic perennials, and few studies have been carried out on bulbils...

Zygospore formation in different strains of the Closterium peracerosum-strigosum-littorale complex was examined in this unicellular isogamous charophycean alga to shed light on gametic mating strains in this taxon, which is believed to share a close phylogenetic relationship with land plants. Zygospores typically form as a result of conjugation between mating-type plus (mt(+)) and mating-type minus (mt(-)) cells during sexual reproduction in the heterothallic strain, similar to Chlamydomonas. However, within clonal cells, zygospores are formed within homothallic strains, and the majority of these zygospores originate as a result of conjugation of two recently divided sister gametangial cells derived from one vegetative cell...

To elucidate the functional differences in how Arabidopsis stigmas regulate pollen hydration and germination, we analyzed receptivity of stigmas, epidermal surfaces (leaves, stems of inflorescence bolts, and floral organs), and an abiotic surface (cover glass) for pollen hydration and germination. Using 65% relative humidity (RH), we found that mature pollen grains were able to hydrate and germinate on stigmas at flower developmental stages 9-13, but not on the distal end of pistils at stage 8, epidermal surfaces, or glass...

The grass family (Poaceae) of the monocotyledons includes about 10,000 species and represents one of the most important taxa among angiosperms. Their flower morphology is remarkably different from those of other monocotyledons and higher eudicots. The peculiar floral structure of grasses is the floret, which contains carpels and stamens, like eudicots, but lacks petals and sepals. The reproductive organs are surrounded by two lodicules, which correspond to eudicot petals, and by a palea and lemma, whose correspondence to eudicot organs remains controversial...

Phosphoinositides are important lipids involved in membrane identity, vesicle trafficking, and intracellular signaling. In recent years, phosphoinositides have been shown to play a critical role in polarized secretion in plants, as perturbations of phosphoinositide metabolism, through loss of function mutants, result in defects in root hair elongation and pollen tube growth, where polarized secretion occurs rapidly. In the Brassicaceae, responses of stigmatic papillae to compatible pollen are also thought to involve highly regulated secretory events to facilitate pollen hydration and penetration of the pollen tube through the stigmatic surface...

Control of female parthenogenetic apomixis and androsporogenesis of Douglas-fir embryonal initials was studied using an experimental culture system in which changes in growth condition can mediate changes in cell identity and outcomes. This culture system constitutes an artificial sporangium in which myriad culture conditions can be simulated and should be applicable for research on a variety of gymnosperms. In this study, embryonal initials from developing seeds from two Douglas-fir trees were rescued and became reprogrammed for female parthenogenetic apomixis (fPA) and parthenogenetic androsporogenesis (mPA)...

In safflower, the anther wall at maturity consists of a single epidermis, an endothecium, a middle layer and the tapetum. The tapetum consists mainly of a single layer of cells. However, this single-layer appearance is punctuated by loci having 'two-celled' groupings due to additional periclinal divisions in some tapetal cells. Meiotic division in microsporocytes gives rise to tetrads of microspores. The primexine is formed around the protoplasts of microspores while they are still enveloped within the callose wall...

Maize male reproductive development is complex and lengthy, and anther formation and pollen maturation are precisely and spatiotemporally regulated. Here, we document that callose, somatic, and microspore defect 1 (csmd1), a new male-sterile mutant, has both pre-meiotic somatic and post-meiotic gametophyte and somatic defects. Chromosome behavior and cell developmental events were monitored by nuclear staining viewed by bright field microscopy; cell dimensions were charted by Volocity analysis of confocal microscopy images...

Apomixis, an asexual mode of reproduction through seeds, holds much promise for agricultural advances. However, the molecular mechanisms underlying this trait are still poorly understood. We previously isolated several transcripts representing novel sequences differentially expressed in reproductive tissues of sexual and apomictic plants. Here, we report the characterization of two of these unknown RNA transcripts (experimental codes N17 and N22). Since original fragments showed no significant homologies to sequences at databases, preliminary genomic PCR experiments were carried out to discard possible contaminations...

Silene latifolia is dioecious, yet rare hermaphrodites have been found, and such natural mutants can provide valuable insight into genetic mechanisms. Here, we describe a hermaphrodite-inducing mutation that is almost certainly localized to the gynoecium-suppression region of the Y chromosome in S. latifolia. The mutant Y chromosome was passed through the megaspore, and the presence of two X chromosomes was not necessary for seed development in the parent. This result supports a lack of degeneration of the Y chromosome in S...

Over the course of maize evolution, domestication played a major role in the structural transition of the vegetative and reproductive characteristics that distinguish it from its closest wild relative, Zea mays subsp. parviglumis (Balsas teosinte). Little is known, however, about impacts of the domestication process on the cellular features of the female gametophyte and the subsequent reproductive events after fertilization, even though they are essential components of plant sexual reproduction. In this study, we investigated the developmental and cellular features of the Balsas teosinte female gametophyte and early developing seed in order to unravel the key structural and evolutionary transitions of the reproductive process associated with the domestication of the ancestor of maize...

Angiosperms are characterized by the occurrence of double fertilization. However, Podostemaceae is considered an exception with the presence of only single fertilization (syngamy) though two male gametes are formed conventionally. To determine the cause for the failure of double fertilization in Dalzellia zeylanica (Gardn.) Wight, we closely tracked the movement of the male gametes from the time of pollen tube initiation to the time of entry into the megagametophyte to affect fertilization. We report for the first time, the presence of a novel type of three-nucleate/three-celled mature megagametophyte consisting of two synergids and an egg cell in D...

Hybrid aspen (Populus tremula × P. tremuloides) belong to the section Populus. Eastern cottonwood (P. deltoides) is a member of the section Aigeiros within the genus Populus. These poplar sections are generally considered to be incompatible. Here, we describe successful hybridisation between these parents, producing an offspring family with 27 individuals. The hybrid character of individuals was proven by genotypes at 16 nuclear microsatellite loci. One individual was suspected to have more than the diploid chromosome number of 2n = 38 due to the observation of more than two alleles at several loci...

The tomato clade within the genus Solanum has numerous advantages for mechanistic studies of reproductive isolation. Its thirteen closely related species, along with four closely allied Solanum species, provide a defined group with diverse mating systems that display complex interspecific reproductive barriers. Several kinds of pre- and postzygotic barriers have already been identified within this clade. Well-developed genetic maps, introgression lines, interspecific bridging lines, and the newly available draft genome sequence of the domesticated tomato (Solanum lycopersicum) are valuable tools for the genetic analysis of interspecific reproductive barriers...