Howlett B J, Rolls B D, Cozijnsen A J
Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Parkville, Vic., Australia.
Microbiol Res. 1997 Sep;152(3):261-7. doi: 10.1016/S0944-5013(97)80038-9.
In the ascomycete Leptosphaeria maculans tandem repeats of ribosomal DNA (rDNA) are restricted to one or two particular chromosomes of the 15 chromosomes of 19 field isolates examined. Ribosomal DNA can account for size differences of 35% between homologous chromosomes in a particular tetrad. During crossing, no detectable recombination between blocks of tandem repeats, nor changes in their size occur. The organisation of rDNA in L. maculans differs from many other haploid fungi. Firstly, sequence heterogeneity occurs within tandem repeats of rDNA; regularly spaced Sal 1 sites (0.25 Mb apart) are present within a 1.4 Mb block of tandem repeats. Secondly, individual isolates have different-sized rDNA repeats; this variation occurs in the non-transcribed intergenic spacer region. Thirdly, there is a wide range in the copy number of the rDNA repeat (from 56 to 225) amongst only four field isolates examined.
在所研究的19个田间分离株的15条染色体中,子囊菌黄斑小球腔菌(Leptosphaeria maculans)的核糖体DNA(rDNA)串联重复序列仅局限于其中一两条特定染色体上。核糖体DNA能够解释特定四分体中同源染色体之间35%的大小差异。在杂交过程中,串联重复序列块之间未检测到重组现象,其大小也未发生变化。黄斑小球腔菌中rDNA的组织形式与许多其他单倍体真菌不同。首先,rDNA串联重复序列内存在序列异质性;在一个1.4 Mb的串联重复序列块内,存在规则间隔的Sal 1位点(相隔0.25 Mb)。其次,单个分离株具有不同大小的rDNA重复序列;这种变异发生在非转录间隔区。第三,在所检测的仅四个田间分离株中,rDNA重复序列的拷贝数范围很广(从56到225)。