RESUMEN
Mating of Blakeslea trispora and other molds of the order Mucorales requires the interaction of mycelia of opposite sex, (+) and (-), leading to the development of specialized structures and to an enhanced accumulation of beta-carotene. Industry obtains beta-carotene by co-cultivating appropriate strains of Blakeslea ("mated cultures"). Gene transcription in single and mated cultures was assayed by cDNA-AFLP, a technique to observe the differential expression of subsets of mRNA fragments. Overexpression in mated cultures is about ten times more frequent than underexpression. We obtained and sequenced fragments of 97 candidate genes that appeared to be overexpressed during mating and confirmed four of them by reverse transcription and real-time PCR. Comparisons with gene sequences from other organisms suggest functions in carotene biosynthesis (4 genes), energy metabolism (8), cell wall synthesis (1), transfer of acetyl groups (1), and regulatory processes (10). Sodium acetate inhibited sexual overexpression in about two-thirds of the candidate genes and acted as a signal with broad effects on the metabolism and the morphology of mated cultures. Our work offers new materials for the study of carotene biosynthesis and its regulation and for the improvement of carotene production with Mucorales.
Asunto(s)
Carotenoides/biosíntesis , Genes Fúngicos , Mucorales/fisiología , Reproducción , Secuencia de Bases , Cartilla de ADN , ADN Complementario , Electroforesis en Gel de Poliacrilamida , Perfilación de la Expresión Génica , Mucorales/genética , Mucorales/metabolismo , Transcripción GenéticaRESUMEN
The fungus Aspergillus niger is an industrial producer of pectin-degrading enzymes. The recent solving of the genomic sequence of A. niger allowed an inventory of the entire genome of the fungus for potential carbohydrate-degrading enzymes. By applying bioinformatics tools, 12 new genes, putatively encoding family 28 glycoside hydrolases, were identified. Seven of the newly discovered genes form a new gene group, which we show to encode exoacting pectinolytic glycoside hydrolases. This group includes four exo-polygalacturonan hydrolases (PGAX, PGXA, PGXB and PGXC) and three putative exo-rhamnogalacturonan hydrolases (RGXA, RGXB and RGXC). Biochemical identification using polygalacturonic acid and xylogalacturonan as substrates demonstrated that indeed PGXB and PGXC act as exo-polygalacturonases, whereas PGXA acts as an exo-xylogalacturonan hydrolase. The expression levels of all 21 genes were assessed by microarray analysis. The results from the present study demonstrate that exo-acting glycoside hydrolases play a prominent role in pectin degradation.
Asunto(s)
Aspergillus niger/enzimología , Proteínas Fúngicas/metabolismo , Glicósido Hidrolasas/metabolismo , Pectinas/metabolismo , Acetilesterasa/genética , Acetilesterasa/metabolismo , Secuencia de Aminoácidos , Aspergillus niger/efectos de los fármacos , Aspergillus niger/genética , Carbohidratos/farmacología , ADN de Hongos/química , ADN de Hongos/genética , Proteínas Fúngicas/genética , Regulación Enzimológica de la Expresión Génica/efectos de los fármacos , Regulación Fúngica de la Expresión Génica/efectos de los fármacos , Genoma Fúngico/genética , Glicósido Hidrolasas/genética , Concentración de Iones de Hidrógeno , Isoenzimas/genética , Isoenzimas/metabolismo , Datos de Secuencia Molecular , Análisis de Secuencia por Matrices de Oligonucleótidos , Filogenia , ARN Mensajero/genética , ARN Mensajero/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Alineación de Secuencia , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Especificidad por SustratoRESUMEN
A gene has been cloned from Xanthophyllomyces dendrorhous by complementation of astaxanthin formation in a beta-carotene accumulating mutant. It consists of 3,166 bp and contains 17 introns. For the beta-carotene mutant ATCC 96815, a single point mutation in the splicing sequence of intron 8 was found. The resulting improper splicing of the mRNA results in an inactive protein. The cDNA of this beta-carotene oxygenase encodes a cytochrome P450 monooxygenase belonging to the 3A subfamily. P450-specific domains were identified including a cytochrome P450 and an oxygen binding motif. Electrons are provided by a cytochrome P450 reductase. Functional characterization of the enzyme by genetic modification of X. dendrorhous demonstrated that this P450 monooxygenase is multifunctional catalyzing all steps from beta-carotene to astaxanthin formation by oxygenation of carbon 3 and 4. The reaction sequence is first 4-ketolation of beta-carotene followed by 3-hydroxylation. A hydroxylation mechanism at allylic carbon atoms has been proposed for the generation of 4-keto and 3-hydroxy groups at both beta-ionone ends.