No description available.

Polyphenol oxidases (PPOs) are ubiquitous enzymes that oxidize phenols to quinones in the presence of molecular oxygen, often leading to tissue discolouration. They are sometimes considered as defense proteins but other functions, for example in phenolic compound biosynthesis, have also been found. In this thesis, bioinformatic searches were conducted to identify putative PPO genes from available genomes representing five Viridiplantae lineages: chlorophytes, bryophytes, lycophytes, monocotyledonous anthophytes and eudicotyledonous anthophytes. Duplicated PPO genes were found in most land plant genomes. A detailed investigation of the poplar (Populus trichocarpa) PPO gene family found nine genes that exhibit differential expression profiles during development and following stress, of which PtrPPO1 was the only significant wound-inducible PPO gene. A phylogenetic reconstruction of the poplar PPOs identified PtrPPO13 to be an unusual PPO homolog and it was studied in detail. Experimental evidence indicated that PtrPPO13 is expressed in most organs, and unlike most PPOs, is localized to the vacuole. Together, the phylogeny, gene expression and subcellular localization studies suggest that PPOs are likely to have variable physiological functions in plants and that PtrPPO13 is distinct from most typical PPOs. / Graduate / 0309

The AGC group of protein kinases (named for protein kinases A, G, and C) is found in all eukaryotes studied so far, and its members coordinate essential cellular processes including translation, metabolism, hormone response, growth, and survival. AGC kinases are intensively studied in mammals because of their connection with human diseases like cancer, diabetes, and neurological disorders. Some aspects of AGC kinase function are organism-specific, but others are conserved in highly divergent species. Several AGC kinases are regulated by the conserved 3-phosphoinositide dependent protein kinase-1 (PDK1), which is itself an AGC kinase. PDK1 regulates its substrates through phosphorylation at a conserved site in their activation loop. Here, I identify and characterize a PDK1 homologue from the moss Physcomitrella patens (PpPDK1). I show PpPDK1 phosphorylates plant AGC kinases in the activation loop, but unexpectedly lacks a lipid-binding domain, suggesting that its regulation differs from other species. In contrast to mammalian cells, PpPDK1 is not an essential gene, suggesting that AGC kinase pathways in P. patens are sufficient for survival even in the absence of activation by PpPDK1. I analyze putative PDK1 sequences from 100 different eukaryotic species, finding that many PDK1s differ from the "conventional" PDK1 found in humans. Phylogenetic analysis of these sequences suggests a complicated evolutionary history for PDK1, with the potential for unexpected functional and regulatory features. I also investigate the regulation of Adi3, an AGC kinase from tomato, through phosphorylation by PDK1. I identify a novel putative PDK1 phosphorylation site outside the kinase domain, which appears to increase Adi3 activity on a substrate. Finally, I produce a mutant version of Adi3 that can selectively utilize bulky ATP analogues. This analogue-sensitive protein may be used in a future search for direct Adi3 substrates. Together, my experiments provide insight into two members of the AGC group of protein kinases, one (PDK1) that is conserved in all eukaryotes and one (Adi3) that appears to be present only in plants. These experiments give a new perspective in our view of plant AGC kinase function and regulation.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2001. / Includes bibliographical references.

Spores are single-celled dispersal units surrounded by a wall of the highly resistant biopolymer sporopollenin. All land plants produce spores. Spore development is described in Physcomitrella patens, a moss with single-celled spores, and Dendroceros, a hornwort with multicellular spores. Correlated light, fluorescence and immuno-electron microscopy localizes callose in the aperture of developing spores in the model moss Physcomitrella. Twelve copies of callose synthase genes were annotated bioinformatically and compared with Arabidopsis callose synthase genes. This study identifies a suspect gene involved in moss spore exine development. Unicellular spores of Dendroceros following meiosis remain in tetrads, fill the intercapsular space, and are surrounded by a convoluted, homogeneous electron-opaque outer wall and narrow fibrillar inner wall. No precise pattern of cell division leads to multicellular spores of variable shape and cell number. Evolution of precocious endospory in epiphytic hornworts is a means to protect nascent spores while it develops biochemical and structural machinary to withstand drying. To advance knowledge of genetic control of spore wall development, the sequenced genome of Physcomitrella is probed using a bioinformatic approach to decipher the evolution of five selected genes putatively involved in spore wall formation. Those encoding for callose synthase provide the most complete results. Callose involvement in spore development is a plesiomorphic feature of land plants. Phylogenomic analysis of callose synthases in land plants with sequenced genomes revealed a single moss callose synthase basal in a clade containing the only Arabidopsis callose synthase implicated in exine development of pollen walls as well as two clades of moss specific callose synthase proteins. A predicted protein-protein interactome was constructed to investigate the protein landscape in Physcomitrella for proteins involved in sporogenesis. Orthologous genes were identified between Physcomitrellaand several other species to map orthologous interactions and predict the first bryophyte interactome. The Physcomitrella predicted protein-protein interactome contains 41,936 unique interactions for 4062 different proteins, none of which are associated with sporogenesis. Rather the most conserved interactions among proteins were those associated with metabolic processes. The utility of predicted protein interactions to infer biological roles, providing provisional molecular roadmaps is demonstrated to generate hypotheses for experimental approaches.

Chez les plantes vasculaires, le métabolisme des phénylpropanoïdes conduit à la synthèse de précurseurs de biopolymères structuraux tels que la lignine, ainsi que de nombreux composés antioxydants et anti-UV. Ce métabolisme phénolique est apparu lors de la colonisation des terres par les plantes et a été critique pour leur adaptation à ce nouvel environnement. Physcomitrella patens, une bryophyte phylogénétiquement proche des premières plantes terrestres, est un bon modèle pour l'étude de certains caractères ancestraux. P. patens est dépourvue de lignine. En combinant des approches phylogénomique, génétique et biochimique, ce travail démontre le rôle essentiel de deux BAHD hydroxycinnamoyl tranférases dans le métabolisme phénolique de la mousse et la formation de précurseurs de la cuticule, une couche hydrophobe qui recouvre les parties aériennes de la plante et lui confère une imperméabilité. Il suggère également que deux hydroxycinnamoyl transférases sont requises pour la formation des composés phénoliques solubles accumulés par la mousse. Une exploration préliminaire du métabolisme des flavonoïdes chez ce modèle révèle d’autre part le caractère incomplet et primitif de cette voie métabolique. / In vascular plants, the phenylpropanoid metabolism leads to the synthesis of precursors of structural biopolymers such as lignin and of essential antioxidants and UV screens. The phenolic pathway leading to these compounds appeared upon plant land colonization and is thought critical for their adaptation to this new environment. Physcomitrella patens is a bryophyte, an early-diverging land plant and thus a good model to reveal ancestral traits. P. patens is devoid of lignin. Combining phylogenomic, genetic and biochemical approaches, this work demonstrates the essential role of two BAHD hydroxycinnamoyl transferases in the moss phenolic metabolism and in the formation of precursors of the cuticle, a hydrophobic layer, covering and conferring impermeability to the aerial parts of the plant. It also suggests that two nonredundant hydroxycinnamoyl transferases are required for the formation of the soluble phenolic compounds accumulated in moss. A preliminary exploration of the flavonoid metabolism in this model in addition reveals primitive features of this metabolic route.

No description available.

Anandamide, N-arachidonylethanolamide (NAE 20:4), is an endocannabinoid receptor ligand unique to animals, in which it influences a wide range of physiological and behavioral functions. Using selective lipidomics approach, we recently identified occurrence of anandamide or NAE 20:4 and its precursor in moss plants. While Nacylethanolamines (NAEs) with C12-C18 acyl chain are ubiquitous in seed plants and play a role in mediating abscisic acid (ABA)-dependent or -independent responses to stress, endocannabinoid receptor-mediated interactions, similar to that of animals, have not been elucidated for plants. Physcomitrella patens provides us with a unique opportunity to address if 1) early land plants, such as mosses, retained NAE-mediated signaling mechanism that is akin to animals but not to vascular plants and 2) if such distinctive NAE profile and mechanisms by which it may function in moss plants is responsible, in part, for their natural ability to resist high temperatures and tolerate osmotic and salt stresses and dehydration. Our current studies are focused on characterization of anandamide metabolic pathway and its functional role in the development of moss. Insights into unique lipid composition and signaling pathways that mosses acquired naturally, during their successful transition from water to land, may lead to development of tools necessary to enhance abiotic stress tolerance in other plants.

No description available.

No description available.