Status of ZMM proteins in <i>L</i>. <i>waltii</i> in reference to <i>S</i>. <i>cerevisiae</i> and <i>L</i>. <i>kluyveri</i>.

(XLSX)</p

Variation of the meiotic recombination landscape and properties over a broad evolutionary distance in yeasts

<div><p>Meiotic recombination is a major factor of genome evolution, deeply characterized in only a few model species, notably the yeast <i>Saccharomyces cerevisiae</i>. Consequently, little is known about variations of its properties across species. In this respect, we explored the recombination landscape of <i>Lachancea kluyveri</i>, a protoploid yeast species that diverged from the <i>Saccharomyces</i> genus more than 100 million years ago and we found striking differences with <i>S</i>. <i>cerevisiae</i>. These variations include a lower recombination rate, a higher frequency of chromosomes segregating without any crossover and the absence of recombination on the chromosome arm containing the sex locus. In addition, although well conserved within the <i>Saccharomyces</i> clade, the <i>S</i>. <i>cerevisiae</i> recombination hotspots are not conserved over a broader evolutionary distance. Finally and strikingly, we found evidence of frequent reversal of commitment to meiosis, resulting in return to mitotic growth after allele shuffling. Identification of this major but underestimated evolutionary phenomenon illustrates the relevance of exploring non-model species.</p></div

Comparison of the number of proximal COs between <i>S</i>. <i>cerevisiae</i> and <i>L</i>. <i>kluyveri</i> orthologs.

<p>For each ortholog pair, we determined the number of COs in a 10kb window around each gene. The plot displays the density of ortholog pairs according to the associated number of proximal COs. The conservation of COs position between species would generate a linear correlation, with several instances located in the upper-right part of the plot. Here, the R² of the linear regression is 1.16×10⁻³ (<i>P</i> = 8.22×10⁻³). The unique common hotspot between the two species is <i>MSC7-VMA10-BCD1</i>.</p

Principle of return to mitotic growth (RTG) after an aborted meiosis followed by a second successful meiosis.

<p>After prophase I and inter homolog meiotic recombination, meiosis progression is aborted and chromosomes segregate mitotically by sister chromatid separation only keeping centromeres heterozygous. The resulting diploid cell, if it still has <i>MAT</i>a/<i>MAT</i>α genotype, can go through a second meiosis. Single COs from the first meiotic prophase are converted into double COs potentially associated with short 4:0 conversion tracts. LOH tracts are converted into large 4:0 segregating tracts. Precise location of COs occurring within LOH tracts cannot be determined.</p

Distribution of LOH events across the 49 sequenced tetrads.

<p>(A) Location of the LOH regions along the genome for each tetrad. Colors correspond to the allelic version conserved. Tetrads flagged by a red dot do not carry any LOH. The two tetrads flagged by a black star have all their centromeres included in LOH regions. (B) Frequency of LOH events along the genome across the 49 tetrads using a 5kb sliding window. The frequency of LOH conserving NBRC10955 alleles (blue area) is added to the frequency of LOH conserving 67–588 alleles (orange area) to provide the total frequency of LOH events along the genome. (C) Frequency of LOHips along the genome using a 5 kb window. Region 5 is a hotspot of LOHips and overlaps with the <i>VMA1</i> gene. A total of 470 LOHips were detected across the 38 tetrads with LOH.</p

Visualization of meiotic DSB hotspots on <i>L</i>. <i>kluyveri</i> chromosomes C, D and E.

<p><i>L</i>. <i>kluyveri</i> meiotic chromosomes were separated by PFGE and revealed with telomere proximal probes after Southern blot. The strain CBS10367 <i>Δsae2</i>/<i>Δsae2</i> was used for a better visualization of the broken chromosomes. Left parts, ethidium bromide stained gels. Right parts, radioactive signals of the corresponding membranes after Southern blot. M, molecular size marker corresponding to mitotic <i>S</i>. <i>cerevisiae</i> chromosomes. Chromosomes are represented vertically, with the location of the probe used. Grey dots indicate centromeres location. Note that the exposure of chromosome C was increased compared to chromosome D and E to better visualize the centromeric proximal DSB hotspot. This underlines the weaker DSB level on chromosome C.</p