Analysis of communication pathways during seed development in Arabidopsis thaliana

Seed development in flowering plants requires coordination between the two genetically different fertilization products, the embryo and the endosperm and the surrounding maternal tissues, the integuments. However, little is known about the coordination of endosperm and embryo growth. In Arabidopsis, mutations in the cell cycle regulator CYCLIN DEPENDENT KINASE A;1 (CKDA;1) result in pollen that only successfully fertilizes the egg cell and seeds generated from crosses with cdka;1 pollen develop endosperm with solely maternal contribution. Here, fertilization by the cdka;1 mutant pollen was used to dissect early seed development. Crosses of 14 Arabidopsis accessions pollinated with cdka;1 mutant pollen revealed a large natural genetic variation with regard to the development of endosperm without paternal contribution. This work revealed a surprisingly large degree of autonomy in embryo growth, but also showed the embryo’s growth restrictions with regard to endosperm size. By using a recombinant inbred line population between the two Arabidopsis accessions Bayreuth-0 and Shahdara four QTLs were discovered, two main and four complex loci that influence the development of unfertilized endosperm. The genes of two DNA N-glycosylases ROS1 and DME, which catalyze the demethylation of symmetrical cytosine methylation, lay inside the two intervals of one of the two complex QTLs. A functional analysis revealed a new aspect of ROS1 and DME in restricting the proliferation of unfertilized endosperm. Moreover, ros1-dme double mutants could rescue the observed seed abortion upon cdka;1 pollination dependent on the activity of the methyltransferase MET1 during the sporophytic phase. Surprisingly, the rescue was independent of dme co-transmission, indicating an effect of ros1 together with dme in trans. The inheritance pattern of the mutant phenotypes revealed a paramutation-like phenomenon and the detection of almost 100% relative methylation levels on PHE1 and AGL36 sequence loci in ros1-dme double compared to the single mutants and Col-0 wild-type plants suggested that hypermethylation caused the mutant phenotype. The observed hypermethylation is likely to be established by in trans interactions between homologous DNA sequences on different chromosomes in a dominant paternal manner. These findings confirm previous results that endosperm formation is, beside other factors, triggered by the alteration of methylation levels prior to fertilization. Furthermore, DNA methylation patterns can probably be transferred via the paternal gametes, influencing not only the epigenetic status of the sporophyte, but also of the following gametophyte and affecting seed development after subsequent fertilization

Male fertility in Arabidopsis requires active DNA demethylation of genes that control pollen tube function.

Active DNA demethylation is required for sexual reproduction in plants but the molecular determinants underlying this epigenetic control are not known. Here, we show in Arabidopsis thaliana that the DNA glycosylases DEMETER (DME) and REPRESSOR OF SILENCING 1 (ROS1) act semi-redundantly in the vegetative cell of pollen to demethylate DNA and ensure proper pollen tube progression. Moreover, we identify six pollen-specific genes with increased DNA methylation as well as reduced expression in dme and dme;ros1. We further show that for four of these genes, reinstalling their expression individually in mutant pollen is sufficient to improve male fertility. Our findings demonstrate an essential role of active DNA demethylation in regulating genes involved in pollen function

Effects of APETALA2 on embryo, endosperm, and seed coat development determine seed size in Arabidopsis

Arabidopsis APETALA2 (AP2) controls seed mass maternally, with ap2 mutants producing larger seeds than wild type. Here, we show that AP2 influences development of the three major seed compartments: embryo, endosperm, and seed coat. AP2 appears to have a significant effect on endosperm development. ap2 mutant seeds undergo an extended period of rapid endosperm growth early in development relative to wild type. This early expanded growth period in ap2 seeds is associated with delayed endosperm cellularization and overgrowth of the endosperm central vacuole. The subsequent period of moderate endosperm growth is also extended in ap2 seeds largely due to persistent cell divisions at the endosperm periphery. The effect of AP2 on endosperm development is mediated by different mechanisms than parent-of-origin effects on seed size observed in interploidy crosses. Seed coat development is affected; integument cells of ap2 mutants are more elongated than wild type. We conclude that endosperm overgrowth and/or integument cell elongation create a larger postfertilization embryo sac into which the ap2 embryo can grow. Morphological development of the embryo is initially delayed in ap2 compared with wild-type seeds, but ap2 embryos become larger than wild type after the bent-cotyledon stage of development. ap2 embryos are able to fill the enlarged postfertilization embryo sac, because they undergo extended periods of cell proliferation and seed filling. We discuss potential mechanisms by which maternally acting AP2 influences development of the zygotic embryo and endosperm to repress seed size

Genome-Wide Transcript Profiling of Endosperm without Paternal Contribution Identifies Parent-of-Origin–Dependent Regulation of AGAMOUS-LIKE36

Seed development in angiosperms is dependent on the interplay among different transcriptional programs operating in the embryo, the endosperm, and the maternally-derived seed coat. In angiosperms, the embryo and the endosperm are products of double fertilization during which the two pollen sperm cells fuse with the egg cell and the central cell of the female gametophyte. In Arabidopsis, analyses of mutants in the cell-cycle regulator CYCLIN DEPENDENT KINASE A;1 (CKDA;1) have revealed the importance of a paternal genome for the effective development of the endosperm and ultimately the seed. Here we have exploited cdka;1 fertilization as a novel tool for the identification of seed regulators and factors involved in parent-of-origin–specific regulation during seed development. We have generated genome-wide transcription profiles of cdka;1 fertilized seeds and identified approximately 600 genes that are downregulated in the absence of a paternal genome. Among those, AGAMOUS-LIKE (AGL) genes encoding Type-I MADS-box transcription factors were significantly overrepresented. Here, AGL36 was chosen for an in-depth study and shown to be imprinted. We demonstrate that AGL36 parent-of-origin–dependent expression is controlled by the activity of METHYLTRANSFERASE1 (MET1) maintenance DNA methyltransferase and DEMETER (DME) DNA glycosylase. Interestingly, our data also show that the active maternal allele of AGL36 is regulated throughout endosperm development by components of the FIS Polycomb Repressive Complex 2 (PRC2), revealing a new type of dual epigenetic regulation in seeds

Equine metabolic syndrome

Laminitis is one of the most common and frustrating clinical presentations in equine practice. While the principles of treatment for laminitis have not changed for several decades, there have been some important paradigm shifts in our understanding of laminitis. Most importantly, it is essential to consider laminitis as a clinical sign of disease and not as a disease in its own right. Once this shift in thinking has occurred, it is logical to then question what disease caused the laminitis. More than 90 per cent of horses presented with laminitis as their primary clinical sign will have developed it as a consequence of endocrine disease; most commonly equine metabolic syndrome (EMS). Given the fact that many horses will have painful protracted and/or chronic recurrent disease, a good understanding of the predisposing factors and how to diagnose and manage them is crucial. Current evidence suggests that early diagnosis and effective management of EMS should be a key aim for practising veterinary surgeons to prevent the devastating consequences of laminitis. This review will focus on EMS, its diagnosis and management

Dynamic Programming Based Segmentation in Biomedical Imaging

Many applications in biomedical imaging have a demand on automatic detection of lines, contours, or boundaries of bones, organs, vessels, and cells. Aim is to support expert decisions in interactive applications or to include it as part of a processing pipeline for automatic image analysis. Biomedical images often suffer from noisy data and fuzzy edges. Therefore, there is a need for robust methods for contour and line detection. Dynamic programming is a popular technique that satisfies these requirements in many ways. This work gives a brief overview over approaches and applications that utilize dynamic programming to solve problems in the challenging field of biomedical imaging. Keywords: Dynamic programming, Active contours, Energy minimization, Shortest path, Segmentation, Contour detectio

Dynamic Programming Based Segmentation in Biomedical Imaging

Many applications in biomedical imaging have a demand on automatic detection of lines, contours, or boundaries of bones, organs, vessels, and cells. Aim is to support expert decisions in interactive applications or to include it as part of a processing pipeline for automatic image analysis. Biomedical images often suffer from noisy data and fuzzy edges. Therefore, there is a need for robust methods for contour and line detection. Dynamic programming is a popular technique that satisfies these requirements in many ways. This work gives a brief overview over approaches and applications that utilize dynamic programming to solve problems in the challenging field of biomedical imaging