Morphological changes, alteration of photosynthetic parameters and chlorophyll production induced by infection with alfalfa dwarf virus in Medicago sativa plants

In Argentina, infections by alfalfa dwarf virus (ADV) affect the cultivation of alfalfa, which is globally one of the most important forage plants. The main objective of this study was to improve current understanding of the underlying mechanisms related to the dwarfism phenotype developed during viral infection. Hydrogen peroxide production, callose deposition and PR5 gene expression levels were evaluated to determine if ADV induces plant defence responses. At the morphological level, higher epicuticular wax production and an increase in proliferation of cells from the fundamental parenchyma were observed when plants were infected by ADV. Infected plants had reduced photosynthesis, stomatal conductance and transpiration/evaporation rate, but interestingly the production of chlorophylls was induced. Finally, using transcriptional analysis, ADV was observed to negatively affect the expression of genes related to synthesis of auxins, cytokinins and brassinosteroids. These results suggest that ADV infection induces a hormonal imbalance leading to an increase in chlorophyll pigment synthesis, stomatal closure and generation of tissue deformation. Overall, the results show a morphological, physiological and photosynthetic characterization of dwarf plants affected by ADV.Fil: Jaime, Camila Lourdes. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias. Departamento de Producción Animal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Muchut, Sebastián Elías. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Reutemann Arnolfo, Andrea Guadalupe. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Gieco, J.. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias. Departamento de Producción Animal; ArgentinaFil: Dunger, Ricardo German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias. Departamento de Producción Animal; Argentin

The Xanthomonas type IV pilus

Type IV pili, a special class of bacterial surface filaments, are key behavioral mediators for many important human pathogens. However, we know very little about the role of these structures in the lifestyles of plant-associated bacteria. Over the past few years, several groups studying the extensive genus of Xanthomonas spp. have gained insights into the roles of played by type IV pili in bacteria-host interactions and pathogenesis, motility, biofilm formation, and interactions with bacteriophages. Protein-protein interaction studies have identified T4P regulators and these, along with structural studies, have begun to reveal some of the possible molecular mechanisms that may control the extension/retraction cycles of these dynamic filaments.Fil: Dunger, Ricardo German. Universidade de Sao Paulo; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; ArgentinaFil: Llontop, Edgar. Universidade de Sao Paulo; BrasilFil: Guzzo, Cristiane R.. Universidade de Sao Paulo; BrasilFil: Farah, Chuck S.. Universidade de Sao Paulo; Brasi

Structure of the PilZ-FimXEAL-c-di-GMP complex responsible for the regulation of bacterial type IV pilus biogenesis

Signal transduction pathways mediated by cyclic-bis(3'→5')-dimeric GMP (c-di-GMP) control many important and complex behaviors in bacteria. C-di-GMP is synthesized through the action of GGDEF domains that possess diguanylate cyclase activity and is degraded by EAL or HD-GYP domains with phosphodiesterase activity. There is mounting evidence that some important c-di-GMP-mediated pathways require protein-protein interactions between members of the GGDEF, EAL, HD-GYP and PilZ protein domain families. For example, interactions have been observed between PilZ and the EAL domain from FimX of Xanthomonas citri (Xac). FimX and PilZ are involved in the regulation of type IV pilus biogenesis via interactions of the latter with the hexameric PilB ATPase associated with the bacterial inner membrane. Here, we present the crystal structure of the ternary complex made up of PilZ, the FimX EAL domain (FimXEAL) and c-di-GMP. PilZ interacts principally with the lobe region and the N-terminal linker helix of the FimXEAL. These interactions involve a hydrophobic surface made up of amino acids conserved in a non-canonical family of PilZ domains that lack intrinsic c-di-GMP binding ability and strand complementation that joins β-sheets from both proteins. Interestingly, the c-di-GMP binds to isolated FimXEAL and to the PilZ-FimXEAL complex in a novel conformation encountered in c-di-GMP-protein complexes in which one of the two glycosidic bonds is in a rare syn conformation while the other adopts the more common anti conformation. The structure points to a means by which c-di-GMP and PilZ binding could be coupled to FimX and PilB conformational statesFundação de Amparo à Pesquisa do Estado de São Paulo, 2011/07777-5Fundação de Amparo à Pesquisa do Estado de São Paulo, 2009/14477-8Fundação de Amparo à Pesquisa do Estado de São Paulo, 2011/22571-

The Xanthomonas citri pv. citri Type VI Secretion System is Induced During Epiphytic Colonization of Citrus

Xanthomonas citri pv. citri (X. citri pv. citri) is the causal agent of Asiatic citrus canker and infects economically important citrus crops. X. citri pv. citri contains one type VI secretion system (T6SS) required for resistance to predation by the soil amoeba Dictyostelium discoideum and induced by the ECF sigma factor EcfK in the presence of amoeba. In this work, we describe the analysis of T6SS gene expression during interaction with host plants. We show that T6SS genes and the cognate positive regulator ecfK are upregulated during growth in the plant surface (epiphytic) and maintain low expression levels during growth inside plant mesophyll. In addition, expression of the virulence-associated T3SS is also induced during epiphytic growth and shows a temporal induction pattern during growth inside plant leaves. The T6SS is not required for adhesion to leaf surface and bioflm formation during the frst stages of plant colonization nor for killing of yeasts cells. Since the phyllosphere is colonized by eukaryotic predators of bacteria, induction of the X. citri pv. citri anti-amoeba T6SS during epiphytic growth suggests the presence of an environmental signal that triggers the resistance phenotype.Fil: Ceseti, Lucas M.. Universidade Estadual de Campinas. Instituto de Biología; BrasilFil: de Santana, Eliane S.. Universidade Estadual de Campinas. Instituto de Biología; BrasilFil: Ratagami, Camila Y.. Universidade Estadual de Campinas. Instituto de Biología; BrasilFil: Barreiros, Yasmin. Universidade Estadual de Campinas. Instituto de Biología; BrasilFil: Lima, Lídia Dos Passos. Universidade Estadual de Campinas. Instituto de Biología; BrasilFil: Dunger, Ricardo German. Universidade do Sao Paulo. Departamento de Bioquímica; Brasil. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias. Departamento de Producción Animal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Farah, Chuck S.. Universidade do Sao Paulo. Departamento de Bioquímica; BrasilFil: Alvarez Martinez, Cristina E.. Universidade Estadual de Campinas. Instituto de Biología; Brasi