Identification of virulence genes in the corn pathogen Colletotrichum graminicola by Agrobacterium tumefaciens-mediated transformation.

A previously developed Agrobacterium tumefaciens-mediated transformation (ATMT) protocol for the plant pathogenic fungus Colletotrichum graminicola led to high rates of tandem integration of the whole Ti-plasmid, and was therefore considered to be unsuitable for the identification of pathogenicity and virulence genes by insertional mutagenesis in this pathogen. We used a modified ATMT protocol with acetosyringone present only during the co-cultivation of C. graminicola and A. tumefaciens. Analysis of 105 single-spore isolates randomly chosen from a collection of approximately 2000 transformants, indicated that almost 70% of the transformants had single T-DNA integrations. Of 500 independent transformants tested, 10 exhibited attenuated virulence in infection assays on whole plants. Microscopic analyses primarily revealed defects at different pre-penetration stages of infection-related morphogenesis. Three transformants were characterized in detail. The identification of the T-DNA integration sites was performed by amplification of genomic DNA ends after endonuclease digestion and polynucleotide tailing. In one transformant, the T-DNA had integrated into the 5'-flank of a gene with similarity to allantoicase genes of other Ascomycota. In the second and third transformants, the T-DNA had integrated into an open reading frame (ORF) and into the 5'-flank of an ORF. In both cases, the ORFs have unknown function.

CHD8 interacts with CHD7, a protein which is mutated in CHARGE syndrome.

CHARGE syndrome is an autosomal dominant disorder caused in about two-third of cases by mutations in the CHD7 gene. For other genetic diseases e.g. hereditary spastic paraplegia, it was shown that interacting partners are involved in the underlying cause of the disease. These data encouraged us to search for CHD7 binding partners by a yeast two-hybrid library screen and CHD8 was identified as an interacting partner. The result was confirmed by a direct yeast two-hybrid analysis, co-immunoprecipitation studies and by a bimolecular fluorescence complementation assay. To investigate the function of CHD7 missense mutations in the CHD7-CHD8 interacting area on the binding capacity of both proteins, we included three known missense mutations (p.His2096Arg, p.Val2102Ile and p.Gly2108Arg) and one newly identified missense mutation (p.Trp2091Arg) in the CHD7 gene and performed both direct yeast two-hybrid and co-immunoprecipitation studies. In the direct yeast two-hybrid system, the CHD7-CHD8 interaction was disrupted by the missense mutations p.Trp2091Arg, p.His2096Arg and p.Gly2108Arg, whereas in the co-immunoprecipitation studies disruption of the CHD7-CHD8 interaction by the mutations could not be observed. The results lead to the hypothesis that CHD7 and CHD8 proteins are interacting directly and indirectly via additional linker proteins. Disruption of the direct CHD7-CHD8 interaction might change the conformation of a putative large CHD7-CHD8 complex and could be a disease mechanism in CHARGE syndrome.