RESUMO
Innate immunity to microorganisms relies on the specific sensing of pathogen-associated molecules by host recognition receptors. Whereas studies in animals have largely focused on the recognition of extracellular pathogen-associated molecules by the TLR (toll-like receptor) superfamily, few studies have been carried out in plants, and it is not understood how these molecules are secreted or modified. The rice Xa21 gene encodes a receptor-like kinase that provides immunity against strains of the bacterial pathogen Xanthomonas oryzae pv. oryzae carrying AvrXa21 activity. We identified four X. oryzae pv. oryzae genes that are required for AvrXa21 activity. raxA, raxB, and raxC encode proteins with similarity to a membrane fusion protein, an ATP-binding cassette transporter, and an outer membrane protein, respectively, of bacterial type I secretion systems. The fourth gene, raxST, encodes a sulfotransferase-like protein. Sequence analysis of three naturally occurring X. oryzae pv. oryzae strains no longer recognized by Xa21 revealed alterations in the raxST and raxA genes. The raxC gene complemented an Escherichia coli tolC mutant for secretion of a double glycine-leader peptide confirming the function of raxC in type I secretion. These results indicate that bacterial type I secretion is necessary for Xa21-mediated recognition and immunity and further suggest that type I secretion and modification of pathogen-associated molecules play an important role in triggering the innate immune response in rice.
Assuntos
Genes Bacterianos , Oryza/imunologia , Oryza/microbiologia , Proteínas de Plantas/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Xanthomonas/genética , Sequência de Aminoácidos , Proteínas da Membrana Bacteriana Externa/genética , Colicinas/metabolismo , Proteínas de Escherichia coli , Teste de Complementação Genética , Proteínas de Membrana Transportadoras , Dados de Sequência Molecular , Mutação , Fases de Leitura Aberta , Oryza/enzimologia , Filogenia , Homologia de Sequência de Aminoácidos , Sulfotransferases/genética , Xanthomonas/metabolismo , Xanthomonas/patogenicidadeRESUMO
Thermostable enzymes and thermophilic cell factories may afford economic advantages in the production of many chemicals and biomass-based fuels. Here we describe and compare the genomes of two thermophilic fungi, Myceliophthora thermophila and Thielavia terrestris. To our knowledge, these genomes are the first described for thermophilic eukaryotes and the first complete telomere-to-telomere genomes for filamentous fungi. Genome analyses and experimental data suggest that both thermophiles are capable of hydrolyzing all major polysaccharides found in biomass. Examination of transcriptome data and secreted proteins suggests that the two fungi use shared approaches in the hydrolysis of cellulose and xylan but distinct mechanisms in pectin degradation. Characterization of the biomass-hydrolyzing activity of recombinant enzymes suggests that these organisms are highly efficient in biomass decomposition at both moderate and high temperatures. Furthermore, we present evidence suggesting that aside from representing a potential reservoir of thermostable enzymes, thermophilic fungi are amenable to manipulation using classical and molecular genetics.
Assuntos
Ascomicetos/genética , Biomassa , Genoma Fúngico/genética , Genômica/métodos , Temperatura , Ascomicetos/enzimologia , Ascomicetos/crescimento & desenvolvimento , Biodegradação Ambiental , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Regulação Fúngica da Expressão Gênica , Hidrólise , Medicago sativa/metabolismo , Modelos Genéticos , Dados de Sequência Molecular , Filogenia , Polissacarídeos/metabolismo , Proteoma/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Transcrição GênicaRESUMO
Trichoderma reesei is the main industrial source of cellulases and hemicellulases used to depolymerize biomass to simple sugars that are converted to chemical intermediates and biofuels, such as ethanol. We assembled 89 scaffolds (sets of ordered and oriented contigs) to generate 34 Mbp of nearly contiguous T. reesei genome sequence comprising 9,129 predicted gene models. Unexpectedly, considering the industrial utility and effectiveness of the carbohydrate-active enzymes of T. reesei, its genome encodes fewer cellulases and hemicellulases than any other sequenced fungus able to hydrolyze plant cell wall polysaccharides. Many T. reesei genes encoding carbohydrate-active enzymes are distributed nonrandomly in clusters that lie between regions of synteny with other Sordariomycetes. Numerous genes encoding biosynthetic pathways for secondary metabolites may promote survival of T. reesei in its competitive soil habitat, but genome analysis provided little mechanistic insight into its extraordinary capacity for protein secretion. Our analysis, coupled with the genome sequence data, provides a roadmap for constructing enhanced T. reesei strains for industrial applications such as biofuel production.