Comparative transcriptomics of seed nourishing tissues: uncovering conserved and divergent pathways in seed plants.

The evolutionary and ecological success of spermatophytes is intrinsically linked to the seed habit, which provides a protective environment for the initial development of the new generation. This environment includes an ephemeral nourishing tissue that supports embryo growth. In gymnosperms this tissue originates from the asexual proliferation of the maternal megagametophyte, while in angiosperms it is a product of fertilization, and is called the endosperm.

Endosperm and Seed Transcriptomes Reveal Possible Roles for Small RNA Pathways in Wild Tomato Hybrid Seed Failure.

Crosses between the wild tomato species Solanum peruvianum and Solanum chilense result in hybrid seed failure (HSF), characterized by endosperm misdevelopment and embryo arrest. We previously showed that genomic imprinting, the parent-of-origin-dependent expression of alleles, is perturbed in the hybrid endosperm, with many of the normally paternally expressed genes losing their imprinted status. Here, we report transcriptome-based analyses of gene and small RNA (sRNA) expression levels.

Population Genomics of the "Arcanum" Species Group in Wild Tomatoes: Evidence for Separate Origins of Two Self-Compatible Lineages.

Given their diverse mating systems and recent divergence, wild tomatoes ( section ) have become an attractive model system to study ecological divergence, the build-up of reproductive barriers, and the causes and consequences of the breakdown of self-incompatibility. Here we report on a lesser-studied group of species known as the "Arcanum" group, comprising the nominal species , , and . The latter two taxa are self-compatible but are thought to self-fertilize at different rates, given their distinct manifestations of the morphological "selfing syndrome.

A revival of effective ploidy: the asymmetry of parental roles in endosperm-based hybridization barriers.

Interest in understanding hybrid seed failure (HSF) has mushroomed, both in terms of identifying underlying molecular processes and their evolutionary drivers. We review phenotypic and molecular advances with a focus on the 'effective ploidy' concept, witnessing a recent revival after long obscurity. Endosperm misdevelopment has now been shown to underlie HSF in many inter-specific, homoploid crosses.

Laser-Assisted Microdissection of Plant Embryos for Transcriptional Profiling.

Transcriptomic studies have proven powerful and effective as a tool to study the molecular underpinnings of plant development. Still, it remains challenging to disentangle cell- or tissue-specific transcriptomes in complex structures like the plant seed. In particular, the embryo of flowering plants is embedded in the endosperm, a nurturing tissue, which, in turn, is enclosed by the maternal seed coat.

The Genus as a Resource for Apomixis Research.

The genera (A. Löve et D. Löve) and , the latter containing the model plant , belong to the same clade within the Brassicaceae family.

Differences in Effective Ploidy Drive Genome-Wide Endosperm Expression Polarization and Seed Failure in Wild Tomato Hybrids.

Parental imbalances in the endosperm leading to impaired development and eventual hybrid seed failure are common causes of postzygotic isolation in flowering plants. Endosperm sensitivity to parental dosage is reflected by canonical phenotypes of "parental excess" in reciprocal interploid crosses. Moreover, parental-excess traits are also evident in many homoploid interspecific crosses, potentially reflecting among-lineage variation in "effective ploidy" driven by endosperm properties.

Wild tomato endosperm transcriptomes reveal common roles of genomic imprinting in both nuclear and cellular endosperm.

Genomic imprinting is a conspicuous feature of the endosperm, a triploid tissue nurturing the embryo and synchronizing angiosperm seed development. An unknown subset of imprinted genes (IGs) is critical for successful seed development and should have highly conserved functions. Recent genome-wide studies have found limited conservation of IGs among distantly related species, but there is a paucity of data from closely related lineages.

Incidence and developmental timing of endosperm failure in post-zygotic isolation between wild tomato lineages.

Background And Aims: Defective hybrid seed development in angiosperms might mediate the rapid establishment of intrinsic post-zygotic isolation between closely related species. Extensive crosses within and among three lineages of wild tomatoes (Solanum section Lycopersicon) were performed to address the incidence, developmental timing and histological manifestations of hybrid seed failure. These lineages encompass different, yet fairly recent, divergence times and both allopatric and partially sympatric pairs.

Genomic Imprinting in the Endosperm Is Systematically Perturbed in Abortive Hybrid Tomato Seeds.

Hybrid seed failure represents an important postzygotic barrier to interbreeding among species of wild tomatoes (Solanum section Lycopersicon) and other flowering plants. We studied genome-wide changes associated with hybrid seed abortion in the closely related Solanum peruvianum and S. chilense where hybrid crosses yield high proportions of inviable seeds due to endosperm failure and arrested embryo development.

Laser-assisted Microdissection (LAM) as a Tool for Transcriptional Profiling of Individual Cell Types.

The understanding of developmental processes at the molecular level requires insights into transcriptional regulation, and thus the transcriptome, at the level of individual cell types. While the methods described here are generally applicable to a wide range of species and cell types, our research focuses on plant reproduction. Plant cultivation and seed production is of crucial importance for human and animal nutrition.

Testing for "snowballing" hybrid incompatibilities in Solanum: impact of ancestral polymorphism and divergence estimates.

Two recent high-profile studies offered empirical evidence for a "snowballing" accumulation of postzygotic incompatibilities in Drosophila and Solanum (tomatoes). Here we present a reanalysis of the Solanum data that is motivated by population genetic principles. Specifically, the high levels of intraspecific nucleotide polymorphism in wild tomato species and presumably large effective population size throughout the divergence history of this clade imply that ancestral polymorphism should be taken into account when evaluating sequence divergence between species.