RESUMO

Trichoderma virens is a ubiquitous soil fungus successfully used in biological control due to its efficient colonization of plant roots. In fungi, 4-phosphopantetheinyl transferases (PPTases) activate enzymes involved in primary and secondary metabolism. Therefore, we cloned the PPTase gene ppt1 from T. virens and generated PPTase-deficient (?ppt1) and overexpressing strains to investigate the role of this enzyme in biocontrol and induction of plant defense responses. The ?ppt1 mutants were auxotrophic for lysine, produced nonpigmented conidia, and were unable to synthesize nonribosomal peptides. Although spore germination was severely compromised under both low and high iron availability, mycelial growth occurred faster than the wild type, and the mutants were able to efficiently colonize plant roots. The ?ppt1 mutants were unable of inhibiting growth of phytopathogenic fungi in vitro. Arabidopsis thaliana seedlings co-cultivated with wild-type T. virens showed increased expression of pPr1a:uidA and pLox2:uidA markers, which correlated with enhanced accumulation of salicylic acid (SA), jasmonic acid, camalexin, and resistance to Botrytis cinerea. Co-cultivation of A. thaliana seedlings with ?ppt1 mutants compromised the SA and camalexin responses, resulting in decreased protection against the pathogen. Our data reveal an important role of T. virens PPT1 in antibiosis and induction of SA and camalexin-dependent plant defense responses.

Assuntos

Proteínas de Bactérias/metabolismo , Botrytis/fisiologia , Doenças das Plantas/microbiologia , Imunidade Vegetal , Transferases (Outros Grupos de Fosfato Substituídos)/metabolismo , Trichoderma/enzimologia , Antibiose , Arabidopsis/imunologia , Arabidopsis/metabolismo , Arabidopsis/microbiologia , Proteínas de Bactérias/genética , Expressão Gênica , Regulação da Expressão Gênica no Desenvolvimento , Regulação Fúngica da Expressão Gênica , Regulação da Expressão Gênica de Plantas , Teste de Complementação Genética , Indóis/análise , Indóis/metabolismo , Solanum lycopersicum/microbiologia , Solanum lycopersicum/fisiologia , Mutação , Raízes de Plantas/microbiologia , Raízes de Plantas/fisiologia , Ácido Salicílico/metabolismo , Sementes/microbiologia , Sementes/fisiologia , Esporos Fúngicos , Tiazóis/análise , Tiazóis/metabolismo , Transferases (Outros Grupos de Fosfato Substituídos)/genética , Trichoderma/genética , Trichoderma/crescimento & desenvolvimento , Trichoderma/fisiologia

RESUMO

Studies on Rhizobium-legume symbiosis show that trehalose content in nodules under drought stress correlates positively with an increase in plant tolerance to this stress. Fewer reports describe trehalose accumulation in mycorrhiza where, in contrast with rhizobia, there is no flux of carbohydrates from the microsymbiont to the plant. However, the trehalose dynamics in the Mycorrhiza-Rhizobium-Legume tripartite symbiosis is unknown. The present study explores the role of this tripartite symbiosis in the trehalose content of nodules grown under contrasting moisture conditions. Three wild genotypes (P. filiformis, P. acutifolis and P. vulgaris) and two commercial genotypes of Phaseolus vulgaris (Pinto villa and Flor de Mayo) were used. Co-inoculation treatments were conducted with Glomus intraradices and a mixture of seven native rhizobial strains, and trehalose content was determined by GC/MS. The results showed a negative effect of mycorrhizal inoculation on nodule development, as mycorrhized plants showed fewer nodules and lower nodule dry weight compared to plants inoculated only with Rhizobium. Mycorrhizal colonization was also higher in plants inoculated only with Glomus as compared to plants co-inoculated with both microsymbionts. In regard to trehalose, co-inoculation negatively affects its accumulation in the nodules of each genotype tested. However, the correlation analysis showed a significantly positive correlation between mycorrhizal colonization and nodule trehalose content.

RESUMO

Phosphorus (P) is one of the most important nutrients limiting agricultural production worldwide. In acid and alkaline soils, which make up over 70% of the world's arable land, P forms insoluble compounds that are not available for plant use. To reduce P deficiencies and ensure plant productivity, nearly 30 million tons of P fertilizer are applied every year. Up to 80% of the applied P fertilizer is lost because it becomes immobile and unavailable for plant uptake. Therefore, the development of novel plant varieties more efficient in the use of P represents the best alternative to reduce the use of P fertilizers and achieve a more sustainable agriculture. We show here that the ability to use insoluble P compounds can be significantly enhanced by engineering plants to produce more organic acids. Our results show that when compared to the controls, citrate-overproducing plants yield more leaf and fruit biomass when grown under P-limiting conditions and require less P fertilizer to achieve optimal growth.

Assuntos

Citrato (si)-Sintase/genética , Citrato (si)-Sintase/metabolismo , Citratos/metabolismo , Nicotiana/fisiologia , Fosfatos/metabolismo , Fósforo/metabolismo , Plantas Geneticamente Modificadas/metabolismo , Plantas Tóxicas , Transporte Biológico , Caulimovirus/genética , Concentração de Íons de Hidrogênio , Regiões Promotoras Genéticas , Pseudomonas aeruginosa/enzimologia , Pseudomonas aeruginosa/genética , Proteínas Recombinantes/metabolismo , Rhizobium , Solo , Nicotiana/enzimologia , Nicotiana/genética

RESUMO

During the last 20 years increasing experimental evidence has associated organic acid metabolism with plant tolerance to environmental stress. Current knowledge shows that organic acids not only act as intermediates in carbon metabolism but also as key components in mechanisms that some plants use to cope with nutrient deficiencies, metal tolerance and plant-microbe interactions operating at the root-soil interphase. In this review we summarize recent knowledge on the physiology and occurrence of organic acids in plants and their special relevance concerning nitrate reduction, phosphorus and iron acquisition, aluminum tolerance and soil ecology. We also discuss novel findings in relation to the biotechnological manipulation of organic acids in transgenic models ranging from cell cultures to whole plants. This novel perspective of organic acid metabolism and its potential manipulation may represent a way to understand fundamental aspects of plant physiology and lead to new strategies to obtain crop varieties better adapted to environmental and mineral stress.