Compatibility Loci Research Articles

Structure Analysis of the MatA Locus of Sexual Compatibility in the Edible Mushroom Pleurotus ostreatus

The edible oyster mushroom Pleurotus ostreatus is one of the most cultivated species worldwide. Morphogenesis associated with the maturation of fruit bodies is controlled by two unlinked loci of sexual compatibility matA and matB with multiple alleles (tetrapolar system of sexual compatibility). Quantitative analysis of the alleles of mating compatibility loci in 17 natural isolates collected in the Moscow region was performed in mon–mon (monokaryons–monokaryon) and di–mon (dikaryon–monokaryon) crossings. Four monokaryotic testers strains which were heteroallelic at both mating type loci were obtained for each of the five natural mushroom isolates by using original technique of sterile spore prints on Petri dishes and mon–mon crossing. Twelve natural isolates were crossed via di-mon mating with the four monokaryotic testers M-38. Genetic analysis of the alleles of sexual compatibility loci in 17 natural isolates revealed multiple alleles at both loci: at least ten alleles at matA locus and eight alleles at matB locus. Structural organization analysis of the matA locus was performed in silico for homokaryotic strains PC9 and PC15 based on the whole-genome sequencing data available at DOE Joint Genome Institute. The matA locus has an extremely divergent structure: there are one copy of the homeodomain gene hd1 and one copy of the hd2 gene in the PC9 strain, whereas the matA locus of the PC15 strain is composed by two copies of hd1.1 and hd1.2 genes (class HD1 homeodomain proteins) and one copy of hd2 gene (class HD2 proteins). Comprehensive analysis of amino acid sequences of HD1 and HD2 homeodomain proteins demonstrated that the proteins have a globular structure with the nuclear localization and contain a variable N-terminus and a more conserved DNA-binding domain with a specific conserved motif WFXNXR in the third ɑ-helix. The results suggest that multiple alleles of the matA locus of sexual compatibility in basidiomycete fungi is achieved due to both different copy number of the coding hd genes within the locus and the variability of the coding gene sequences.

Structure Analysis of the <i>MatA</i> Locus of Sexual Compatibility in the Edible Mushroom <i>Pleurotus ostreatus</i>

The edible oyster mushroom Pleurotus ostreatus is one of the most cultivated species worldwide. Morphogenesis associated with the fruit bodies maturation is controlled by two unlinked loci of sexual compatibility matA and matB with multiple alleles (tetrapolar system of sexual compatibility). Quantitative analysis of the alleles of mating compatibility loci in 17 natural isolates collected in the Moscow region was performed in mon-mon (monokaryon – monokaryon) and di-mon (dikaryon – monokaryon) crossings. Four monokaryotic testers strains which were heteroallelic at both mating type loci were obtained for each of the five natural mushroom isolates by using original technique of sterile spore prints on Petri dishes and mon-mon crossing. Twelve natural isolates were crossed via di-mon mating with the four monokaryotic testers M-38. Genetic analysis of the alleles of sexual compatibility loci in 17 natural isolates revealed multiple alleles at both loci: at least 10 alleles at matA locus and eight alleles at matB locus. Structural organization analysis of the matA locus was performed in silico for homokaryotic strains PC9 and PC15 based on the genome sequencing data available at DOE Joint Genome Institute. The matA locus is proved to be of extremely divergent structure: there are one copy of the homeodomain gene hd1 and one copy of the hd2 gene in the PC9 strain, whereas the matA locus of the PC15 strain is composed by two copies of hd1.1 and hd1.2 genes (class HD1 homeodomain proteins) and one copy of hd2 gene (class HD2 proteins). Comprehensive analysis of amino acid sequences of HD1 and HD2 homeodomain proteins demonstrated that the proteins have a globular structure with the nuclear localization and contain a variable N-terminus and the more conservative DNA-binding domain with a specific conservative motif WFXNXR in the third ɑ-helix. The results approve the opinion that multiple alleles of the matA locus of sexual compatibility in basidiomycete fungi is achieved by different copies’ number of the coding hd genes within the locus, as well as by the variability of the coding gene sequences.

Convergent recombination cessation between mating-type genes and centromeres in selfing anther-smut fungi.

The degree of selfing has major impacts on adaptability and is often controlled by molecular mechanisms determining mating compatibility. Changes in compatibility systems are therefore important evolutionary events, but their underlying genomic mechanisms are often poorly understood. Fungi display frequent shifts in compatibility systems, and their small genomes facilitate elucidation of the mechanisms involved. In particular, linkage between the pre- and postmating compatibility loci has evolved repeatedly, increasing the odds of gamete compatibility under selfing. Here, we studied the mating-type chromosomes of two anther-smut fungi with unlinked mating-type loci despite a self-fertilization mating system. Segregation analyses and comparisons of high-quality genome assemblies revealed that these two species displayed linkage between mating-type loci and their respective centromeres. This arrangement renders the same improved odds of gamete compatibility as direct linkage of the two mating-type loci under the automictic mating (intratetrad selfing) of anther-smut fungi. Recombination cessation was found associated with a large inversion in only one of the four linkage events. The lack of trans-specific polymorphism at genes located in nonrecombining regions and linkage date estimates indicated that the events of recombination cessation occurred independently in the two sister species. Our study shows that natural selection can repeatedly lead to similar genomic patterns and phenotypes, and that different evolutionary paths can lead to distinct yet equally beneficial responses to selection. Our study further highlights that automixis and gene linkage to centromeres have important genetic and evolutionary consequences, while being poorly recognized despite being present in a broad range of taxa.

The chromosome 11 olfactory receptor gene cluster is a candidate reproductive partner-specific compatibility locus

The chromosome 11 olfactory receptor gene cluster is a candidate reproductive partner-specific compatibility locus

Sea star populations diverge by positive selection at a sperm-egg compatibility locus.

Fertilization proteins of marine broadcast spawning species often show signals of positive selection. Among geographically isolated populations, positive selection within populations can lead to differences between them, and may result in reproductive isolation upon secondary contact. Here, we test for positive selection in the reproductive compatibility locus, bindin, in two populations of a sea star on either side of a phylogeographic break. We find evidence for positive selection at codon sites in both populations, which are under neutral or purifying selection in the reciprocal population. The signal of positive selection is stronger and more robust in the population where effective population size is larger and bindin diversity is greater. In addition, we find high variation in coding sequence length caused by large indels at two repetitive domains within the gene, with greater length diversity in the larger population. These findings provide evidence of population-divergent positive selection in a fertilization compatibility locus, and suggest that sexual selection can lead to reproductive divergence between conspecific marine populations.

Characterization of Fusarium oxysporum f.sp. cepae from Onion in Turkey Based on Vegetative Compatibility and rDNA RFLP Analysis

Seventy-five isolates of Fusarium oxysporum f.sp. cepae, the causal agent of basal plate rot on onion, were obtained from seven provinces of Turkey. The isolates were characterized by vegetative compatibility grouping (VCGs) and restriction fragment length polymorphism (RFLP) analysis of the nuclear ribosomal DNA intergenic spacer region (IGS). Forty-eight vegetative compatibility groups were found, each containing a single isolate. Only one isolate formed strong heterokaryons with the reference isolates of VCG 0423. Five isolates were heterokaryon self-incompatible. Restriction fragment analysis with six different enzymes revealed 13 IGS types among 75 F. oxysporum isolates from Turkey as well as 16 reference isolates from Colorado, USA. The majority of single-member VCGs produced identical RFLP banding patterns with minor deviations, considerably different from those of the reference VCG isolates. These results suggested that isolates of F. oxysporum f.sp. cepae in Turkey derived from distinct clonal lineages and mutations at one or more vegetative compatibility loci restrict heterokaryon formation.

Genetic Heterogeneity ofLeucostomaSpecies in Michigan Peach Orchards

ABSTRACT The pathogens causing perennial canker of peach, Leucostoma spp., were characterized in Michigan orchards to identify which species and subgroups (cryptic species) were prevalent on a highly susceptible peach cultivar, Loring, and a less susceptible cultivar, Redhaven. Four hundred and three strains of Leucostoma were isolated from cankers in three southwest Michigan orchards where 'Loring' occurred adjacent to 'Redhaven' in side-by-side plots. Based on colony morphology and small nuclear rDNA size polymorphisms, three cryptic species were detected; 89% of the isolates were identified as L. persoonii phenetic group 1, 10% were L. cincta group 4, and 1% were L. persoonii group 2. Pathogen profiles differed significantly between cankers on small branches of 'Loring' and 'Redhaven', and between cankers on small branches and trunks. Of 1,232 random pairings among isolates of L. persoonii group 1, 95% were vegetatively incompatible. A minimum of 11 and a maximum of 17 maternal lines were identified based upon mitochondrial DNA restriction fragment length polymorphisms among 69 isolates of L. persoonii group 1 from one split-cultivar block of 72 trees. Vegetative compatibility loci were randomly associated with maternal lines. Evidence of clonality was absent in L. persoonii group 1, as no correlation occurred between these two sets of independent genetic markers and no genotype was over-represented. The number of cryptic species, the number of maternal lines, and the frequency of incompatibility within maternal lines indicate that considerable genetic variation exists within the Leucostoma populations in Michigan peach orchards, and that sexual recombination is common.

Rare interspecific hybrids in natural populations of the Dutch elm disease pathogens Ophiostoma ulmi and O. novo-ulmi

Ophiostoma ulmi and O. novo-ulmi are partly reproductively isolated, morphologically, behaviourally and molecularly distinct species responsible for the first and current pandemics of Dutch elm disease, respectively. Among >11000 isolates sampled from Dutch elm disease sites across Eurasia and North America since 1973, nine could not be assigned to O. ulmi or O. novo-ulmi . Of these isolates one (P129) was from Poland and eight (d10, d11, e12, e27, e28, e37, f30 and g3) were from a single bark sample in Portugal. These nine isolates were termed ‘fast-waxy’ isolates because of their unusual cultural characteristics. The possibility that they were interspecific hybrids was investigated. When compared with O. ulmi and O. novo-ulmi for colony pattern, growth-rate, optimum temperature for growth, vascular wilt ability, elm bark colonizing ability, cerato-ulmin toxin production, ability to fertilize (as ♂) O. novo-ulmi , and ability to be fertilized (as ♀) by O. ulmi , they exhibited a combination of O. ulmi -like, O. novo-ulmi -like, intermediate or novel characters (female sterility) consistent with their being hybrids. P129 and representative Portuguese isolates d10 and e27 each exhibited a different combination of characters, indicating each was a different hybrid genotype. When d10 and e27 were independently crossed to the same O. novo-ulmi isolate, differences in their F 1 progeny sets for growth-rate and pathogenicity distributions were consistent with their being different recombinant genotypes. A molecular analysis of P129, d10 and e27 using RAPDs of genomic DNA, rDNA RFLPs and cerato-ulmin gene sequences confirmed that each was a unique interspecific hybrid. The mechanism of origin of these hybrids and their evolutionary significance are discussed. Combined experimental and circumstantial evidence indicates that they are relatively unfit, rare and probably transient, and that they arise when O. novo-ulmi invades territory occupied by O. ulmi and replaces it. Nonetheless, the possibility that the hybrids act as a genetic bridge, facilitating transfer of novel vegetative compatibility loci and other loci form O. ulmi to O. novo-ulmi at recent epidemic fronts, requires investigation.

Expression and Inheritance of Sexual Preference and Selfing Potential inPhytophthora infestans

Mating interactions inPhytophthora infestans,a heterothallic oomycete, are regulated by sexual compatibility loci and a system of sexual preference. The development of gametangial associations in this species were examined using matings between strains containing a β-glucuronidase (GUS) transgene and nontransformed strains. The GUS gene enabled the facile assessment of whether oospores resulted from hybridization between isolates or from self-interactions and allowed measurements of the sexual preference of strains. Depending on the strains being mated, from 5 to 99% of the total oospores formed resulted from outcrossing. In such hybrid pairings, A1 and A2 field isolates generally acted as predominant females and males, respectively. Nevertheless, genetic analyses indicated that sexual preference and compatibility type were determined by unlinked loci. The sexual preference of most strains varied depending on the relative preference of their mating partners. Both sexual preference and the frequency of outcrossing versus self-interactions varied with the position of gametangia within the mating culture.

Relationships Among Pathogenic and Nonpathogenic Isolates ofFusarium oxysporumBased on the Partial Sequence of the Intergenic Spacer Region of the Ribosomal DNA

Using PCR, we amplified and sequenced approximately 1,000 bp of the 5' end of the intergenic spacer (IGS) of the rDNA in 15 isolates of Fusarium oxysporum and one isolate of F. subglutinans. Isolates were selected to represent diversity in our collection based on differences in pathogenic race, vegetative compatibility group (VCG), mitochondrial DNA (mtDNA) haplotype, IGS haplotype, and DNA fingerprint. The objective of this research was to clarify the origin of virulence within F. oxysporum, the relationship between pathogenic and nonpathogenic strains, and the evolution of the different races of F. oxysporum f. sp. melonis. Bootstrapped parsimony analysis of the partial IGS sequence data identified a phylogenetic tree with highly significant branches. The two F. oxysporum f. sp. melonis VCGs, 0131 and 0134, were separated into distinct lineages. Race was not distinguished by significant IGS sequence differences within the pathogen VCGs. One exception was a race 1 isolate which was associated with VCG 0131 but, based on both mtDNA and IGS haplotype, had greater affinity with VCG 0134. Two IGS sequence types were found in this race 1 isolate, one suggesting an affiliation with VCG 0131 and the other similar to isolates in VCG 0134. This may have resulted from past somatic or sexual interactions between F. oxysporum f. sp. melonis, VCGs 0131 and 0134. Nonpathogens that were vegetatively compatible with the pathogen were not closely related to the pathogen based on IGS sequence data. Thus, nonpathogens and pathogens may share common alleles at vegetative compatibility loci by coincidence rather than because of recent clonal derivation from a common ancestor.

Sexuality and Somatic Incompatibility in Phellinus gilvus

Phellinus gilvus was found to have an out-crossing, bifactorial (tetrapolar) mating system. Two types of heterokaryon formation were evident in intrabasidiome homokaryon-homokaryon pairings: 1) bidirectional nuclear migration resulting in the formation of a single heterokaryotic thallus, and 2) restricted nuclear migration with a heterokaryon formed only in the interaction zone between the paired homokaryotic colonies. The mating system of P. gilvus is multiallelic; pairings between homokaryotic isolates from different basidiomes were always compatible with bidirectional nuclear migration. One heterozygous locus had major effects on somatic incompatibility reactions among progeny from two studied fruiting bodies. This was supported by the observation that pairings among sets of heterokaryons composed of one common nonsibling nucleus and the other sib-related resulted in two somatic incompatibility groups, while pairings among sibling heterokaryons resulted in three groups. The sexual compatibility loci were separate from the somatic incompatibility loci and no linkage was found between them.

Sexuality and somatic incompatibility inPhellinus gilvus

Phellinus gilvus was found to have an out? crossing, bifactorial (tetrapolar) mating system. Two types of heterokaryon formation were evident in in- trabasidiome homokaryon-homokaryon pairings: 1) bidirectional nuclear migration resulting in the for? mation of a single heterokaryotic thallus, and 2) re? stricted nuclear migration with a heterokaryon formed only in the interaction zone between the paired homo? karyotic colonies. The mating system of P. gilvus is multiallelic; pairings between homokaryotic isolates from different basidiomes were always compatible with bidirectional nuclear migration. One heterozygous lo? cus had major effects on somatic incompatibility re? actions among progeny from two studied fruiting bod? ies. This was supported by the observation that pair? ings among sets of heterokaryons composed of one common nonsibling nucleus and the other sib-related resulted in two somatic incompatibility groups, while pairings among sibling heterokaryons resulted in three groups. The sexual compatibility loci were separate from the somatic incompatibility loci and no linkage was found between them.

Expression of unilateral incompatibility in pollen of Lycopersicon pennellii is determined by major loci on chromosomes 1, 6 and 10

We have previously described gene introgression from the wild nightshade Solanum lycopersicoides into tomato (Lycopersicon esculentum) through the use of either diploid or sesquidiploid hybrids (the latter consisting of two genomes of L. esculentum and one genome of S. lycopersicoides). Both types of intergeneric hybrids display pollen sterility, but workable ovule fertility. Unilateral incompatibility prevents their direct hybridization with staminate L. esculentum. Pollen of a self-compattible form of the related wild species L. pennellii is compatible with pistils of L. esculentum x S. lycopersicoides hybrids. This trait was backcrossed from L. pennellii to L. esculentum in order to develop bridging lines that could be used to obtain progeny from the intergeneric hybrids and to study the inheritance of bridging ability. In progeny of L. esculentum x S. lycopersicoides hybrids pollinated with L. pennellii-derived bridging lines, preferential transmission of L. pennellii alleles was observed for certain isozyme and RFLP markers on chromosomes 1, 6 and 10. The skewed segregations suggest linkage to three major pollen-expressed compatibility loci. This was confirmed by observations of pollen tube growth, which indicated that compatibility with pistils of the diploid intergeneric hybrid occurred only in bridging lines at least heterozygous for the L. pennellii markers on chromosomes 1, 6 and 10. Compatibility with the sesquidiploid hybrid required only the chromosome 1 and 6 loci, indicating an apparent effect of gene dosage on expression of incompatibility in the pistil. In an F2 L. esculentum x L. pennellii population, preferential transmission of L. pennellii alleles was observed for the same markers on chromosomes 1 and 10, as well as other markers on chromosomes 3, 11, and 12, but not 6. The chromosome 1 pollen compatibility locus maps to or near the S-locus, which determines S-allele specificity. The results are discussed in relation to existing genetic models for unilateral incompatibility, including the possible involvement of the S-locus.

A Third Multiallelic Mating-type Locus in Physarum polycephalum

SUMMARY: Sexual development (crossing) in Physarum polycephalum occurs when two haploid amoebae fuse to form a diploid plasmodium. The imz locus influences the maximum pH at which crossing can occur. A new allele of imz has been identified, bringing the total number of alleles to three. Contrary to earlier findings, it has been shown that all homoallelic combinations of imz alleles display a similar pH limit for crossing, which is lower than that for imz-heteroallelic combinations. It is concluded that imz is a mating compatibility locus; thus the mating-type system of P. polycephalum comprises three multiallelic loci: matA, matB and imz. It is proposed that imz be renamed matC.

TWO MULTIALLELIC MATING COMPATIBILITY LOCI SEPARATELY REGULATE ZYGOTE FORMATION AND ZYGOTE DIFFERENTIATION IN THE MYXOMYCETE PHYSARUM POLYCEPHALUM

The mating of Physarum polycephalum amoebae, the ultimate consequence of which is a "plasmodium," was recently shown to be governed by two compatibility loci, matA (or mt) and matB (Dee 1978; Youngmanet al. 1979). We present evidence that matA and matB separately regulate two discrete stages of mating: in the first stage, amoebae (which are normally haploid) fuse in pairs, with a specificity determined by matB genotype, to form diploid zygotes; subsequent differentiation of the zygotes into plasmodia is regulated by matA and is unaffected by matB. Mixtures of amoebae carrying unlike matA and matB alleles formed diploids to the extent of 10 to 15% of the cells present, and the diploids differentiated into plasmodia. When only the matB alleles differed, diploid cells still formed to a comparable (5 to 10%) extent, but rather than differentiating, these diploids remained amoebae. When strains carried the same alleles of matB, formation of diploid cells was greatly reduced: in like-matB, like-matA mixtures, none of 320 cells examined was diploid; in like-matB, unlike mat-A mixtures, differentiating diploids could be detected, but at only 10(-3) to 10(-2) the frequency of unlike-matB, unlike-matA mixtures. The nondifferentiating diploid amoebae recovered from unlike-matB, like-matA mixtures were genetically stable through extensive growth, even though they grew more slowly than haploids (10-hr vs. 8-hr doubling period), and could be crossed with both haploids and diploids. The results of such higher ploidy and mixed ploidy crosses indicate that karyogamy does not invariably accompany zygote formation and differentiation.

A NEW MATING COMPATIBILITY LOCUS IN PHYSARUM POLYCEPHALUM

The rate and extent of plasmodium formation were studied in mating tests involving pairs of largely isogenic amoebal strains compatible for mating-type (mt) alleles. A systematic variability was observed: plasmodia formed either rapidly and extensively or slowly and inefficiently. Plasmodium formation was found to be 10(3)- to 10(4)-fold more extensive in "rapid" crosses than in "slow" crosses. A genetic analysis revealed that the variability reflects the influence of a multiallelic compatibility locus that determines mating efficiency. This compatibility locus (designated matB), together with the original mating type locus, mt (in this work designated matA), constitute a tetrapolar mating specificity system in Physarum polycephalum.

CYTOPLASMIC INCOMPATIBILITY STUDIES IN THE MYXOMYCETE DIDYMIUM IRIDIS: RECOVERY AND NUCLEAR SURVIVAL IN HETEROKARYONS

At least eleven somatic compatibility loci exist in the myxomycete Didymium iridis. Cell fusion is controlled by at least seven fusion loci (Fus1–Fus7). Cytoplasmic compatibility is controlled by at least four clear‐zone loci (Cz1–Cz4). Plasmodia with identical phenotypes at all seven fusion loci, but different phenotypes at the clear‐zone loci, will fuse temporarily, but fusion is soon blocked by cytoplasmic reactions which prevent complete mixing. Areas which contain cytoplasm from two incompatible Plasmodia become clearly delineated from healthy cytoplasm. Such areas, termed clear zones, have been isolated and found to recover. If clear zones are sectioned into several small pieces, not all pieces will recover, indicating that toxic cytoplasmic reactions have occurred. Plasmodial fusion studies and F1 studies of recovered clear zones indicate that the clear‐zone loci may also control nuclear survival in heterokaryons.

Genetics of Plasmodial Compatibility and Heterokaryosis in Didymium iridis

“Phenotypic” identicalness for certain compatibility loci appears to determine whether or not 2 Didymium iridis plasmodia will fuse when brought into contact. Based on almost 5,000 fusion tests, it...

GENETIC MARKERS AND LINKAGE RELATIONSHIPS FROM TETRAD DATA IN HYPOMYCES SOLANI f. CUCURBITAE

Ten loci were included in linkage studies with Hypomyces solani f. cucurbitae and the following linkage relationships were recognized: (1) compatibility locus (A/a) to a locus for tolerance to the chlorinated nitrobenzenes (cnb-2); (2) locus for femaleness (c) to the locus for maleness (m); and (3) locus for perithecial color (w) to a locus modifying femaleness (stp-4:). Usually parental ditype and tetratype asci were obtained from the cross ♂ × ♀ but the non-parental ditype ascus was found once. The two loci for sex appear to be separated by the centromere to which they both show close linkage. Centromere linkages have also been detected for the compatibility locus and the locus controlling perithecial color.

On the Evolution of Heterothallism in Fungi

Three major types of life cycles in the fungi - homothallism, unbalanced heterothallism, and balanced heterothallism-and their possible evolutionary relationships to each other are discussed in the light of recent genetic discoveries in microorganisms and higher forms. It is concluded that the most likely explanation of the origin of one-locus two-allelic heterothallism in the fungi is to be found in the compound-locus hypothesis. This would involve the occurrence - independently or simultaneously - and association of pseudoallelic self-sterility mutations in a compound locus (of two or more subunits). It is proposed that the compound nature of the multipleallele compatibility loci of bipolar and tetrapolar higher basidiomycetes may have resulted from successive duplications during evolution.