Expression patterns and phylogenetic analysis of two xylanase genes (htxyl1 and htxyl2) from Helminthosporium turcicum, the cause of northern leaf blight of maize

摘要

A xylanase gene (htxyl2) was cloned from Helininthosporium turcicunt, the cause of northern leaf blight of maize by screening the genomic library from the fungus using a similar to500 bp PCR fragment of the gene as a probe. The gene is a second xylanase gene cloned from the fungus and it is different from the previously cloned xylanase gene (htxyll). The two genes are grouped into separate clades in a phylogenetic tree based on DNA sequences. The patterns of htxyll and htxl2 transcript accumulation were studied in vitro with different carbon and nitrogen sources and during infection of maize by the pathogen. In culture high htxyll transcript was detected in mycelium obtained from medium containing birchwood xylan and birchwood xylan plus xylose as sole carbon sources. On the other hand htxyl2 transcript was detected in a medium containing birchwood xylan plus xylose but not in the medium where only birchwood xylan was used as the sole carbon source. Addition of glucose to the basal inducing media had inhibitory effect to the expression of both genes. The htxyll transcript accumulation declined sharply with an increase in concentration of ammonium sulphate and glutamic acid, while increased htxyl2 transcript was observed with an increase in concentrations of the two nitrogen sources. Abundant htxyl2 transcript was detected at early and late stages of infection of maize by Helininthosporium turcicium. On the other hand no detectable htxyll transcript was found in northern blot under the test conditions. This study demonstrated that in H. turcicum xylanolytic system htxyll and htxl2 are differentially expressed and might play important roles in the saprophytic and pathogenic phases of the fungus, respectively. (C) 2003 Elsevier SAS. All rights reserved. [References: 46]