Department of Biomedical Sciences, Microbiology, University of Extremadura, Avda de Elvas s/n, 06006 Badajoz, Spain and.
Department of Biology, Bowdoin College, Brunswick, ME
G3 (Bethesda). 2019 Nov 5;9(11):3631-3644. doi: 10.1534/g3.119.400516.
, the most common fungal pathogen, is a diploid with a genome that is rich in repeats and has high levels of heterozygosity. To study the role of different recombination pathways on direct-repeat recombination, we replaced either allele of the gene (Chr6) with the -blaster cassette (), measured rates of loss as resistance to 5-fluoroorotic acid (5FOA) and used CHEF Southern hybridization and SNP-RFLP analysis to identify recombination mechanisms and their frequency in wildtype and recombination mutants. FOA rates varied little across different strain backgrounds. In contrast, the type and frequency of mechanisms underlying direct repeat recombination varied greatly. For example, wildtype, and strains all displayed a bias for loss via pop-out/deletion inter-homolog recombination and this bias was reduced in mutants. In addition, in -derived 5FOA strains direct repeat recombination was associated with ectopic translocation (5%), chromosome loss/truncation (14%) and inter-homolog recombination (6%). In the absence of , loss was mostly due to chromosome loss and truncation (80-90%), and the bias of retained allele frequency points to the presence of a recessive lethal allele on Chr6B. However, a few single-strand annealing (SSA)-like events were identified and these were independent of either Rad59 or Lig4. Finally, the specific sizes of Chr6 truncations suggest that the inserted URA-blaster could represent a fragile site.
念珠菌属,最常见的真菌病原体,是一个具有丰富重复序列和高度杂合性的二倍体。为了研究不同重组途径在直接重复重组中的作用,我们用 -blaster 盒()替换了基因(Chr6)的两个等位基因,通过对 5-氟乳清酸(5FOA)抗性来测量 丢失率,并利用 CHEF Southern 杂交和 SNP-RFLP 分析来鉴定重组机制及其在野生型和重组突变体中的频率。FOA 率在不同菌株背景下变化不大。相比之下,直接重复重组的机制类型和频率差异很大。例如,野生型、和 菌株都显示出通过弹出/缺失 同源重组丢失的偏向,这种偏向在 突变体中降低。此外,在 -衍生的 5FOA 菌株中,直接重复重组与异位易位(5%)、染色体丢失/截断(14%)和同源重组(6%)有关。在缺乏 的情况下,丢失主要是由于染色体丢失和截断(80-90%),并且保留等位基因频率的偏向指向 Chr6B 上存在隐性致死等位基因。然而,鉴定出了一些类似于单链退火(SSA)的事件,这些事件与 Rad59 或 Lig4 无关。最后,Chr6 截断的特定大小表明插入的 URA-blaster 可能代表一个脆弱位点。