RESUMO
A novel 36-kDa endochitinase named chit36 has been isolated and characterized from Trichoderma harzianum Rifai TM. Partial amino acid sequences from the purified protein were used to clone the fungal cDNA, based on polymerase chain reaction with degenerate primers. The complete open reading frame encodes a 344-amino acid protein which shows 84% similarity to a putative chitinase from Streptomyces coelicolor. Chit36 was overexpressed under the pki1 constitutive promoter from Trichoderma reesei via biolistic transformation of T. harzianum TM. Stable transformants showed expression and endochitinase activity of chit36 in glucose-rich medium. Culture filtrates containing secreted CHIT36 as the sole chitinolytic enzyme completely inhibited the germination of Botrytis cinerea conidia. Growth of Fusarium oxysporum f. sp. melonis and Sclerotium rolfsii were significantly inhibited on agar plates on which the Trichoderma transformants had previously been grown.
Assuntos
Quitinases/isolamento & purificação , Proteínas Fúngicas , Trichoderma/enzimologia , Sequência de Aminoácidos , Antifúngicos/isolamento & purificação , Antifúngicos/farmacologia , Divisão Celular/efeitos dos fármacos , Quitinases/genética , Quitinases/farmacologia , Fusarium/efeitos dos fármacos , Dados de Sequência Molecular , Controle Biológico de Vetores , Doenças das Plantas/microbiologia , Homologia de Sequência de Aminoácidos , Esporos Fúngicos/efeitos dos fármacos , Trichoderma/genéticaRESUMO
Posttranscriptional silencing of chalcone synthase (Chs) genes in petunia transformants occurs by introducing T-DNAs that contain a promoter-driven or promoterless Chs transgene. With the constructs we used, silencing occurs only by T-DNA loci which are composed of two or more T-DNA copies that are arranged as inverted repeats (IRs). Since we are interested in the mechanism by which these IR loci induce silencing, we have analyzed different IR loci and nonsilencing single-copy (S) T-DNA loci with respect to the expression and methylation of the transgenes residing in these loci. We show that in an IR locus, the transgenes located proximal to the IR center are much more highly methylated than are the distal genes. A strong silencing locus composed of three inverted T-DNAs bearing promoterless Chs transgenes was methylated across the entire locus. The host Chs genes in untransformed plants were moderately methylated, and no change in methylation was detected when the genes were silenced. Run-on transcription assays showed that promoter-driven transgenes located proximal to the center of a particular IR are transcriptionally more repressed than are the distal genes of the same IR locus. Transcription of the promoterless Chs transgenes could not be detected. In the primary transformant, some of the IR loci were detected together with an unlinked S locus. We observed that the methylation and expression characteristics of the transgenes of these S loci were comparable to those of the partner IR loci, suggesting that there has been cross talk between the two types of loci. Despite the similar features, S loci are unable to induce silencing, indicating that the palindromic arrangement of the Chs transgenes in the IR loci is critical for silencing. Since transcriptionally silenced transgenes in IRs can trigger posttranscriptional silencing of the host genes, our data are most consistent with a model of silencing in which the transgenes physically interact with the homologous host gene(s). The interaction may alter epigenetic features other than methylation, thereby impairing the regular production of mRNA.
Assuntos
Metilação de DNA , DNA Bacteriano/genética , Genes de Plantas/genética , Sequências Repetitivas de Ácido Nucleico/genética , Transcrição Gênica/genética , Transgenes/genética , Aciltransferases/genética , Regulação da Expressão Gênica de Plantas/genética , Regiões Promotoras Genéticas/genética , RNA Mensageiro/metabolismo , Transformação Genética/genéticaRESUMO
The effect of cucurbitacin and of Ecballium extract on the formation of mRNA coding for laccase was examined in cultures of Botrytis cinerea grown with inducers of laccase formation, in the presence or absence of the inhibitory compounds. RNA was isolated from the cultures and probed with specific DNA probes for laccase. As an internal control, the RNA was probed for Botrytis beta-tubulin mRNA. From an analysis of the results it is clear that cucurbitacin I and Ecballium extract specifically repress the amount of mRNA coding for laccase. This could account for the previously observed repression of laccase formation by cucurbitacins.
