Tip Growth of Plant-Pathogenic Fungi and Tip-Chitin Metabolism

点击翻译按钮获取中文摘要

In Japanese side, we investigated the functions of chitin synthases in tip growth of filamentous fungi. We have isolated four chitin synthase genes (chsA,chsB,chsC,and chsD) from Aspergillus nidulans which belongs to Ascomycete filamentous fungi and two genes (chs1 and chs2) from Rhizopus oligosporus which belongs to Zygomycete filamentous fungi. When we disrupted each one of four chitin synthase genes in the genome of A.nidulans, we detected no difference of the phenotype of these disruptants from that of wild type strain except for the chsB gene disruptant. The tip growth of chsB gene disruptant was severely defected. We constructed each kind of double gene disruptant from the chsA,chsC,and chsD gene disruptants. The frequency of conidiation of the chsA and chsC double gene disruptant and chsA and chsC double gene disruptant were 0.002% and 10% of that of wild type strain, respectively. To test the function of chsB gene product in the conidiation, .open reading frame of chsB gene was … More fused to alcA gene promoter whose expression was regulated by the carbon source in the medium. When the expression of chsB gene was repressed at the conidiation stage, the frequency of conidiation decreased about one-tenth of that of wild type strain. Thus, all of chs gene products are required at the stage of conidiation. The density of hyphae of chsA and chsC double gene disruptant was very rare. It suggests that the gene products of chsA and chsC also function in the hyphae growth.We have isolated a chitinase gene (chiA) from A.nidulans by PCR method and disrupted the gene. The disruptant of chiA gene grew and formed conidia as well as wild type strain. To investigate the phase of expression of the gene, we fused lacZ gene of Escherichia coli to chiA gene and introduced it into A.nidulans. The expression of chiA gene at the conidiation stage was twice as strong as the hyphae growth stage. Thus, it is suggested that chiA gene product function at the both stage.In Korean side, to construct the host-vector system in the plant pathogenic fungi, Pyricularia oryzae, they have isolated some auxotrophic mutants of P.oryzae. They have also isolated a PCR fragment of chitin synthase gene from genomic DNA of P.oryzae whose function in plant pathogenicity is being investigated in Korea.These works have been done in a cooperative manner between our group in Japan and the Korean group. Less