Variation of rDNA Internal Transcribed Spacer Sequences in Rhizoctonia cerealis

Abstract

Fifty-four single protoplast isolates (SPIs) were regenerated from three Rhizoctonia cerealis strains. A total of 169 rDNA-ITS regions were cloned and sequenced from these 54 SPIs. Variations in the ITS1 and ITS2 regions that flank the 5.8S gene were found within clones from the same strain, as well as within clones from the same SPI. These include variations in GC content and ITS length, and single-nucleotide polymorphisms (SNPs). The different strains and SPIs GC contents range from 40.25 to 41.74% and from 42.40 to 45.02%, in the ITS1 and ITS2 regions, respectively. All SNPs occur in the ITS1 and ITS2 regions, with 3-6 and 4-6 polymorphic sites in each region, respectively, in the different strains. SNP variation is relatively stable within the same strain. For example, the 89 ITS sequences generated from isolate WK-207, regardless of SPI or clone, predominantly cluster into two separate clades on a phylogenetic tree, suggesting that nuclei genetic heterogeneity is related to ITS variation in R. cerealis. Although rDNA-ITS sequences from the three strains and different SPIs are somewhat variable, all of our ITS sequences cluster together in anastomosis subgroup AG-DI during phylogenetic analysis. The ITS variation we observed does not negatively influence R. cerealis anastomosis group or subgroup classification.

Keywords: Protoplast preparation; Rhizoctonia cerealis; Variation; rDNA-ITS sequence.