Molecular and Genetic Analysis of the effects of SUMOylation on the regulation of floral transition in Arabidopsis

SUMOylation, the post-translational attachment of SUMO (Small Ubiquitin-like Modifier) to a substrate protein, regulates the activity of several proteins involved in critical cellular processes like cell division and transcriptional regulation. SUMO is subsequently removed from substrates by SUMO-specific proteases, making this modification reversible. In plants, SUMOylation has been implicated in several physiological responses and flowering time control. ESD4 (Early in Short Days 4) encodes a SUMO-specific protease that prevents the accumulation of SUMO-conjugates in Arabidopsis. The esd4-1 mutant shows a very early flowering phenotype as well as several shoot developmental distortions suggesting an important role of SUMOylation in the regulation of plant development. To investigate the role of SUMOylation in flowering time control a suppressor screen of esd4 was performed. 120 independent suppressors of esd4 (sed) were isolated and 15 of them further characterized. The SUMO-conjugate levels of these seds are more similar to those of esd4-1 than to the wild type. Rough map positions for five of these sed mutants were established using classical genetic methods, and combined with Next Generation Sequencing sed111-1 was finemapped to a region of chromosome I that contains only six candidate genes. In a different study, SUMOylation of SHORT VEGETATIVE PHASE (SVP) was assessed and SUMO attachment lysines were determined using E. coli strains that recapitulate the SUMO conjugation pathway. SVP interacts with FLOWERING LOCUS C (FLC) to form a strong floral repressor complex. To study the role of SUMOylation in SVP function, an svp-null mutant (svp-41) was transformed with constructs aiming to hyperSUMOylate (translational fusions with SUMO or AtSCE) or hypoSUMOylate (mutations in the putative SUMO-attachment sites) the SVP protein in transgenic plants. Mutant phenotypes caused by these constructs are discussed

Conservation of the Ustilago maydis effector See1 in related smuts

Ustilago maydis is a biotrophic fungus that induces formation of tumors in maize (Zea mays L). In a recent study we identified See1 (Seedling efficient effector 1) as an U. maydis organ-specific effector required for tumor formation in leaves. See1 is required for U. maydis induced reactivation of plant DNA synthesis during leaf tumor progression. The protein is secreted from biotrophic hyphae and localizes to the cytoplasm and nucleus of plant cell. See1 interacts with maize SGT1, a cell cycle and immune regulator, interfering with its MAPK-triggered phosphorylation. Here, we present new data on the conservation of See1 in other closely related smuts and experimental data on the functionality of See1 ortholog in Ustilago hordei, the causal agent of barley covered smut disease

Cell type specific transcriptional reprogramming of maize leaves during Ustilago maydis induced tumor formation

Ustilago maydis is a biotrophic pathogen and well-established genetic model to understand the molecular basis of biotrophic interactions. U. maydis suppresses plant defense and induces tumors on all aerial parts of its host plant maize. In a previous study we found that U. maydis induced leaf tumor formation builds on two major processes: the induction of hypertrophy in the mesophyll and the induction of cell division (hyperplasia) in the bundle sheath. In this study we analyzed the cell-type specific transcriptome of maize leaves 4 days post infection. This analysis allowed identification of key features underlying the hypertrophic and hyperplasic cell identities derived from mesophyll and bundle sheath cells, respectively. We examined the differentially expressed (DE) genes with particular focus on maize cell cycle genes and found that three A-type cyclins, one B-, D- and T-type are upregulated in the hyperplasic tumorous cells, in which the U. maydis effector protein See1 promotes cell division. Additionally, most of the proteins involved in the formation of the pre-replication complex (pre-RC, that assure that each daughter cell receives identic DNA copies), the transcription factors E2F and DPa as well as several D-type cyclins are deregulated in the hypertrophic cells