The regulatory mechanism of sclerotium differentiation in Rhizoctonia solani

1.携带线状DNA质粒的担子菌立枯丝核菌生长缓慢，致病力弱。草酸的产生与菌核的形成有一定的相关性。在低pH条件下，菌丝生长和菌核形成受到协同抑制，调节pH至5.5可促进菌丝生长和菌核形成。由此可见，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导致培养基的低pH所致。在该真菌中发现的质粒为线状DNA。通过比较限制性内切酶图谱，确定了pRS64-1和pRS64-2两个质粒。这些质粒在几个酶切位点上的限制性内切酶图谱不同，但两个质粒携带的DNA序列是相互杂交的。用限制性内切酶Pst I酶切立枯丝核菌基因组DNA，与标记的质粒片段杂交。基因组DNA约13kb的片段与质粒DNA有一个同源序列。结果表明，该质粒DNA已整合到基因组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.