Search

The genus Oenothera shows an intriguing extent of permanent translocation heterozygosity. Reciprocal translocations of chromosome aims in species or populations result in various kinds of chromosome multivalents in diakinesis. Early meiotic events conditioning such chromosome behaviour are poorly understood. We found a surprising uniformity of the leptotene-diplotene period, regardless of the chromosome configuration at diakinesis (ring of 14, 7 bivalents, mixture of bivalents and multivalents). It appears that the earliest chromosome interactions at Oenothera meiosis are untypical, since they involve pericentromeric regions. During early leptotene, proximal chromosome parts cluster and form a highly polarized Rabl configuration. Telomeres associated in pairs were seen at zygotene. The high degree of polarization of meiotic nuclei continues for an exceptionally long period, i.e., during zygotene-pachytene into the diplotene contraction stage. The Rabl-polarized meiotic architecture and clustering of pericentromeres suggest a high complexity of karyotypes, not only in structural heterozygotes but also in bivalent-forming homozygous species. Key words: translocations, meiosis, Oenothera, permanent translocation heterozygosity, multivalents. Resume : Chez le genre Oenothera, on rencontre une etendue intrigante d'heterozygotie permanente pour des translocations. Des translocations reciproques de bras chromosomiques chez des especes ou des populations produisent divers types de multivalents a la diacinese. Les evenements meiotiques precoces menant a un tel comportement chromosomique sont mal compris. Les auteurs ont observe une etonnante uniformite au cours de la periode leptotene-diplotene, sans egard a la configuration des chromosomes a la diacinese (anneau de 14, sept bivalents, melange de bivalents et de multivalents). Il semble que les toutes premieres interactions chromosomiques au cours de la meiose chez le genre Oenothera soient atypiques puisqu'elles impliquent des regions peri centromeriques. En debut de leptotene, des segments proximaux de chromosomes se rassemblent et forment une configuration Rabl tres polarisee. Des telomeres joints en paires ont ete observes au stade zygotene. L'importante polarisation des noyaux meiotiques se poursuit pendant une periode exceptionnellement longue, c.-a-d. de la phase zygotene-pachytene jusqu'au stade de contraction au diplotene. L'architecture meiotique Rabl polarisee et le regroupement des pericentromeres suggerent une grande complexite caryotypique non seulement chez les heterozygotes structurels, mais aussi chez les especes homozygotes formant des bivalents. Mots-cles : translocations, meiose, Oenothera, heterozygotie permanente pour les translocations, multivalents. [Traduit par la Redaction], Introduction For nearly a century, the genus Oenothera (evening primrose) has been a model for the study of chromosome rearrangements, behaviour, and evolution (Cleland 1972). Individual or multiple reciprocal chromosome [...]

The genus Oenothera has an outstanding scientific tradition. It has been a model for studying aspects of chromosome evolution and speciation, including the impact of plastid nuclear co-evolution. A large collection of strains analyzed during a century of experimental work and unique genetic possibilities allow the exchange of genetically definable plastids, individual or multiple chromosomes, and/or entire haploid genomes (Rennet complexes) between species. However, molecular genetic approaches for the genus are largely lacking. In this study, we describe the development of efficient PCR-based marker systems for both the nuclear genome and the plastome. They allow distinguishing individual chromosomes, Renner complexes, plastomes, and subplastomes. We demonstrate their application by monitoring interspecific exchanges of genomes, chromosome pairs, and/or plastids during crossing programs, e.g., to produce plastome--genome incompatible hybrids. Using an appropriate partial permanent translocation heterozygous hybrid, linkage group 7 of the molecular map could be assigned to chromosome 9.8 of the classical Oenothera map. Finally, we provide the first direct molecular evidence that homologous recombination and free segregation of chromosomes in permanent translocation heterozygous strains is suppressed.

The dissection of quantitative traits into their underlying Mendelian factors has become possible with the aid of molecular markers. In this study, we mapped and characterized quantitative trait loci (QTL) affecting testcross performance of maize (Zea mays L.) and discussed the consistency of these QTL across environments and testers. Two homozygous flint inbred lines were crossed to produce 380 F(sub 2) individuals which were genotyped at 89 restriction fragment length polymorphism (RFLP) marker loci. By selfing the F(sub 2) plants 380 F(sub 3) lines were produced and subsequently crossed to two diverse dent inbred testers (T1 and T2). Each series of testcrosses (TC) was evaluated in field trials with two replications in four environments. Three traits were analyzed: protein content, kernel weight, and plant height. Genotypic and genotype-by-environment interaction variances were highly significant for all traits in both TC series and heritabilities ranged between 0.71 and 0.85. Genotypic correlations between the two TC series were 0.80 (protein content), 0.88 (kernel weight), and 0.84 (plant height). The method of interval mapping was used for characterization of QTL. Protein content was significantly affected by four QTL in TC with T1 explaining 32% of the phenotypic variance (Sigma caret(super 2)(sub p)) and five QTL in TC with T2 explaining 42% of Sigma caret(super 2)(sub p). For kernel weight, eight putative QTL were found in TC with T1 and six were found for T2, explaining about 60% of Sigma caret(super 2)(sub p). Seven QTL explained 52% and four 60% of Sigma caret(super 2)(sub p) for plant height. Results from QTL mapping agreed well across environments. Highly consistent results across testers were obtained for kernel weight and plant height but not for protein content. No significant evidence for epistasis among QTL was found.

Information on genetic relationships among genotypes is of great importance to breeders. In this study we analyzed 29 maize (Zea mays L.) inbreds (18 flint and 11 dent lines) from the European germplasm by means of pedigree and RFLP analyses. Our main objective was to compare Malecot's coancestry (f) based on pedigree data with genetic similarity (GS) based on RFLP data of 188 clone-enzyme combinations (CECs) for their ability to quantify the degree of relatedness among inbreds. Rank correlations between f and GS were highly significant (P < 0.01) for 87 related (f > 0) pairs of flint lines (r(sub s) = 0.71) and for 30 related pairs of dent lines (r(sub s) = 0.86). One dent line was excluded because of likely errors in pedigree detected by RFLP data and confirmed by heterosis data. Based on linear regression of GS on f, coancestry explained 82 and 70% of the variation in GS for related pairs of flint and dent lines, respectively. Therefore, both the coancestry and marker approach are well-suited to (i) measure the average level of relatedness and (ii) identify closely related lines. Observed deviations of GS from its regression on f for individual pairs of lines can be explained by (i) random genetic drift and selection causing unequal genomic contributions of the parents, (ii) random variation of GS estimates due to sampling of the genome by the CECs used, (iii) wide variation in the GS estimates of unrelated lines, and (iv) experimental errors. Provided the genome is sampled by an adequate number (>100) of CECs, RFLP-based GS estimates reflect more accurately the true genetic similarity of a given line pair than f.