The regulatory mechanism of sclerotium differentiation in Rhizoctonia solani

1. 携带线性DNA质粒的担子菌solani Rhizoctonia菌株生长缓慢，致病性弱。草酸的产生与菌核的形成之间存在相关性。在低pH条件下，菌丝生长和菌核形成受到抑制，而在5.5条件下调节pH可促进菌丝生长和菌核形成。由此得出结论，在携带质粒的菌株中观察到的菌核不能形成的原因是由于草酸的产生引起培养基的低pH。在这种真菌中发现的质粒是线性DNA。通过比对酶切图谱，鉴定出两个质粒pRS64-1和pRS64-2。这两个质粒的限制性内切位点不同，但携带同源DNA序列的质粒相互杂交。用限制性内切酶Pst I酶切的茄茄基因组DNA与标记的质粒片段杂交。大约有13千碱基的基因组DNA片段与质粒DNA具有同源序列。结果表明，质粒DNA可能被整合到基因组DNA中。

1. The Basidiomycete Rhizoctonia solani strains which carry the linear DNA plasmids showed slow growth and weak pathogenicity. The correlationship has been observed between the production of oxalic acid and sclerotium formation. Mycelial growth and sclerotium formation were coordinately repressed in low pH media and stimulated by adjusting pH at 5.5. Thus it has been concluded that the inability of sclerotium formation observed in the strains carrying plasmids is resulted from low pH of media caused by the production of oxalic acid.2. The plasmids found in this fungus were linear DNA. Two plasmids, pRS64-1 and pRS64-2 were identified by compairing the restriction maps. The restriction maps of these plasmids were different in several restriction sites, but both plasmids carried homologous DNA sequences hybridized each other.3. Genomic DNA of R. solani digested with a restriction enzyme Pst I was hybridized with the labeled plasmid fragments. Approximately 13 kilobases fragment of genomic DNA has a homologous sequence with the plasmid DNA. The results suggest that the plasmid DNA may be integrated into the genomic DNA.