The exosome is a multi-subunit 3'-5' exonucleolytic complex that is conserved in eukaryotes. The ring-shaped core structure of the exosome is constituted of nine subunits. In yeast, all of nine exosome subunits are essential for viability. On the other hand, in plant, Csl4 is dispensable for growth and development, whereas Rrp41 and Rrp4 are essential for the development of female gametophytes and embryogenesis. Since there has been no report on the exosome itself in filamentous fungi, we attempted to construct the disruptants of genes encoding exosome subunits in Aspergillus oryzae. W e have chosen two orthologous genes for csl4 and rrp4 as targets for disruption, and successfully obtained a csl4 disruptant but not an rrp4 disruptant. The disruption of csl4 gene had no apparent defect on growth in A. oryzae. Since the rrp4 disruptant could not been obtained, this gene would be essential for cell viability. Thus, we generated the conditional rrp4 expression strain by using the promoter of nmtA, expression level of which is regulated by riboswitch existed within its 5'-untranslated region and is repressed considerably in the presence of thiamine. The resultant conditional rrp4 expression strain displayed a remarkable growth defect when thiamine was added to the medium. These results suggested that Rrp4 is essential but Csl4 is not for cell growth in A. oryzae and that function of individual exosome components in A. oryzae is similar to that in plant.
Full conference title:
7th International Aspergillus Meeting
- Asperfest 7 (2010)