Table 1.
List of Saccharomyces strains.
Table 2.
Distribution of S. cerevisiae genes in tetrads from the NBRC 1948-CBS 7001 cross.
Figure 1.
Schematic representation of S. cerevisiae contigs in the genomes S. bayanus CBS380T and NBRC1948.
Black arrows represent to scale genes oriented from the telomere to the centromer and grey arrows genes in the opposite orientation. The junction between S. uvarum and S. cerevisiae chromosomes was indicated by a colour change (white for S. uvarum, grey for S. cerevisiae) within the MAL33 gene of cA. The 5′ ends of contigs A and C were deduced from segregants NBCB-6c and NBCB-6a issued from the cross between strain NBRC1948 and CBS7001.
Figure 2.
Chromosomal localisation of some S. cerevisiae genes in S. bayanus strains.
A, C, E: Electrophoretic karyotypes of yeast strains stained with ethidium bromide. B, D: Southern blot hybridisation on karyotypes A and C, respectively, with probes MTY1 and RTM1 amplified from CBS380T. F, G: Southern blot hybridisation on karyotypes (E) for indicated strains with successively BIO2 and Y' from S288c. Arrow heads indicate chromosomes of S. bayanus (CBS380T and NBRC1948) and S. carlsbergensis (CBS1513) strains revealed by the probes. S. uvarum chromosomes are numbered according to [6].
Table 3.
S. cerevisiae genes transferred in strains of S. bayanus and S. pastorianus.
Figure 3.
Fertility between S. bayanus NBRC1948 and S. uvarum CBS7001.
A: Karyotypes of the constructed hybrid NBCB-10D carrying two chromosome sets of the parent strains. B: Spore viability in 13 tetrads dissected from this S. bayanus/S. uvarum hybrid NBCB-10D. Tetrads are numbered from top to bottom and segregants from left to right. Numbers in bold indicate complete tetrads. C: Electrophoretic karyotypes of the segregants of tetrad NBCB-6 compared with the parent strains NBRC1948 and CBS7001 showing the segregation and recombination of S. bayanus and S. uvarum chromosomes.
Figure 4.
Segregation of S. cerevisiae contigs in four tetrads issued from NBCB-10D.
A and C: Electrophoretic karyotypes of segregant strains and NBRC1948 parent strain stained with Ethidium bromide. B and D: Southern hybridization with RTM1 probe amplified from strain CBS380T.
Table 4.
Sequence comparison of S. uvarum CBS 7001 genes with homologues of different strains of S. bayanus, S. uvarum and S. pastorianus (% nucleotide identity).
Figure 5.
Evolutionary relationships of MET2 and PMA1 in mixed and pure lines.
The evolutionary history was inferred using the Neighbor-Joining method [55]. The optimal trees are shown (MET2: sum of branch length = 0.24619612; PMA1: sum of branch length = 0.09325799). Bootstrap values calculated on 100 replicates are shown next to the branches. A total of 1529 and 2847 nucleotides for MET2 and PMA1, respectively, were used in the final dataset. Two clusters are clearly separated showing their different origins. This underlines the hybrid nature of some S. bayanus strains: NRRL-Y1551, NBRC1948, NBRC539 and S. pastorianus Weihenstephan. S. cerevisiae sequences were used as outgroups.
Figure 6.
Evolutionary relationships of GDH1, ERG10 and HO in mixed and pure lines.
The evolutionary history was inferred as in Figure 5 but with limited number of strains analysed for GDH1, ERG10 and HO. Sequences GDH1 have been obtained in this study and from [5], ERG10 and HO are sequenced in this study except for bayanus-HO and Lg-HO. The optimal tree with the sum of branch length = 0.06421927 is shown. The percentages of replicate trees in which the associated taxa clustered together in the bootstrap test (100 replicates) are shown next to the branches. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Kimura 2-parameter method [61] and are in the units of the number of base substitutions per site. The analysis involved 44 nucleotide sequences. All ambiguous positions were removed for each sequence pair. There were a total of 4382 positions in the final dataset. Strain CBS 380T clustered in lager group based on ERG10 and GDH1 phylogenetic trees.
Figure 7.
Evolutionary relationships of MAL31/MTY in mixed and pure lines.
Phylogenetic tree established using the same method as in Figure 6. MAL3/MTY11 evolution in strain CBS 380T, sequence extracted from cB of the segregant NBCB-6b and MTY1 in cA of the segregant NBCB-6a are considered. In strain NRRLY-1551 only MAL31 allele could be sequenced.
Figure 8.
General scheme deciphering the history of crosses between S. uvarum, S. lagerae and S. cerevisiae.
Current S. bayanus strains are segregants of tetrads issued from a cross S. uvarum x NBRC1948 or a similar strain. Strain NBRC1948 represents a generation hybrid anterior to CBS380T. S. lagerae is the missing species contributor to the genome of strain NBRC1948 or one similar strain. S. lagerae materials reflected by Lg sequences that have been transmitted to S. bayanus and S. pastorianus (Lg presenting 2 to 6% of divergence with S. uvarum sequences).