Cytonuclear interactions remain stable during allopolyploid evolution despite repeated whole-genome duplications in Brassica

Several plastid macromolecular protein complexes are encoded by both nuclear and plastid genes. Therefore, cytonuclear interactions are held in place to prevent genomic conflicts that may lead to incompatibilities. Allopolyploidy resulting from hybridization and genome doubling of two divergent species can disrupt these fine-tuned interactions, as newly formed allopolyploid species confront biparental nuclear chromosomes with a uniparentally inherited plastid genome. To avoid any deleterious effects of unequal genome inheritance, preferential transcription of the plastid donor over the other donor has been hypothesized to occur in allopolyploids. We used Brassica as a model to study the effects of paleopolyploidy in diploid parental species, as well as the effects of recent and ancient allopolyploidy in Brassica napus, on genes implicated in plastid protein complexes. We first identified redundant nuclear copies involved in those complexes. Compared with cytosolic protein complexes and with genome-wide retention rates, genes involved in plastid protein complexes show a higher retention of genes in duplicated and triplicated copies. Those redundant copies are functional and are undergoing strong purifying selection. We then compared transcription patterns and sequences of those redundant gene copies between resynthesized allopolyploids and their diploid parents. The neopolyploids showed no biased subgenome expression or maternal homogenization via gene conversion, despite the presence of some non-synonymous substitutions between plastid genomes of parental progenitors. Instead, subgenome dominance was observed regardless of the maternal progenitor. Our results provide new insights on the evolution of plastid protein complexes that could be tested and generalized in other allopolyploid species

Xe CONGRES INTERNATIONAL SUR LE COLZA Développement et impacts des OGM

Le dernier congrès du Groupe consultatif international de recherches sur le colza s’est déroulé à Canberra (Australie) du 26 septembre au 1er octobre 1999. Pour sa dixième édition, cette manifestation, quadriennale, a réuni plus de 600 participants originaires de 28 pays. La délégation australienne mise en part (35 % des participants), le Canada (15 %) et l’Allemagne (14 %) étaient les pays producteurs les mieux representés suivis de la Grande-Bretagne (6 %), de la France (6 %) et de la Chine (5 %). Résumé en chiffre, le contenu scientifique de ces journées a été apporté par 550 présentations de résultats sous forme d’exposés (166) et de posters (384). Parmi les différents thèmes développés, le thème « amélioration des plantes et biotechnologies » a occupé en nombre d’interventions, à peu près la moitié du congrès (44 %). Les notes suivantes reviennent sur les aspects significatifs de ces présentations. Elles seront suivies dans une prochaine livraison des comptes rendus des thèmes « agronomie », « protection des cultures » et « nutrition ». (Les références au sein des articles renvoient aux textes du CDrom du colloque disponible auprès du Dr Rodney Mailer  : [email protected]

Effets de la structure de l hybride et du fonds génétique sur le taux de recombinaison entre les génomes A de Brassica rapa (AA, 2n=20) et de B. napus (AACC, 2n=38) (Application à l introgression de gènes de résistance à Leptosphaeria maculans dans le colza)

L hybridation interspécifique entre espèces végétales apparentées constitue un bon moyen de réaliser des introgressions de gènes, en vue d augmenter la variabilité génétique d une espèce cultivée. Les recombinaisons génétiques entre les génomes des espèces croisées sont nécessaires pour optimiser les introgressions. Cette étude vise à définir les facteurs agissant sur les fréquences de recombinaison entre les génomes de l espèce tétraploïde Brassica napus (colza, AACC, 2n=38) et de son progéniteur B. rapa (AA, 2n=20) en se basant sur le cas de l introgression de gènes de résistance à Leptosphaeria maculans dans le colza. Après avoir identifié trois gènes de résistance spécifique chez B. rapa, j ai testé les effets de trois faceurs sur les fréquences dans différents croisements. Je n ai trouvé aucun effet de la divergence entre les génomes A de ces deux espèces, mais des effets significatifs du génotype colza et de la structure des hybrides F1. La structure de l hybride F1 a un effet considérable : les hybrides triploïdes AAC, issus du croisement entre B. napus et B. rapa, réalisent à la méiose de 1.8 à 3,4 fois plus de crossing-overs que les hybrides tétraploïdes (AACC), issus du croisement entre colza et colza synthétique (B. rapa (AA) xB. Oleracea (CC)), et 6,1 fois plus de crossing-overs que l espèce diploïde B. rapa.Interspecific hybridization between plant related species is a good way to realise introgressino of genes, in order to increase the genetic variability of cultivated species. Genetic recombinations between genomes of the crossed species are needed to optimise introgressions. This study aims to determine the factors that act on recombination rates in crosses between the allotetraploid species B. napus (AACC, 2n=38), and one of its progenitors, B. rapa (AA, 2n=20), and is based on the study of introgression of resistance genes to Leptosphaeria maculans into B. napus. After having identified three specific resistance genes in B. rapa, I tested the effect of three factors on recombination rates between A genomes of B. rapa and B. napus, by the comparison of the rates obtained in different crosses. I detected no effect of the divergence between A genomes of B. rapa and B. napus, but significant effects of both the B. napus genotype and the structure of F& hybrids. The effet of the hybrid structure was considerable : at the meiosis of AAC triploid hybnrids, resulting from crosses between B. napus and B. rapa, recombination rates were from 1.8 to 3.4 fold higher than in AACC tetrploid hybrids, resulting from crosses between B. napus and a reysnthesized B. napus (B. rapa (AA) x B. oleracea (CC)), and 6.1 fold higher than in the diploid B. rapa species.RENNES-Agrocampus-CRD (352382323) / SudocSudocFranceF

Effets de la structure de l hybride et du fonds génétique sur le taux de recombinaison entre les génomes A de Brassica rapa (AA, 2n=20) et de B. napus (AACC, 2n=38) (Application à l introgression de gènes de résistance à Leptosphaeria maculans dans le colza)

L hybridation interspécifique entre espèces végétales apparentées constitue un bon moyen de réaliser des introgressions de gènes, en vue d augmenter la variabilité génétique d une espèce cultivée. Les recombinaisons génétiques entre les génomes des espèces croisées sont nécessaires pour optimiser les introgressions. Cette étude vise à définir les facteurs agissant sur les fréquences de recombinaison entre les génomes de l espèce tétraploïde Brassica napus (colza, AACC, 2n=38) et de son progéniteur B. rapa (AA, 2n=20) en se basant sur le cas de l introgression de gènes de résistance à Leptosphaeria maculans dans le colza. Après avoir identifié trois gènes de résistance spécifique chez B. rapa, j ai testé les effets de trois faceurs sur les fréquences dans différents croisements. Je n ai trouvé aucun effet de la divergence entre les génomes A de ces deux espèces, mais des effets significatifs du génotype colza et de la structure des hybrides F1. La structure de l hybride F1 a un effet considérable : les hybrides triploïdes AAC, issus du croisement entre B. napus et B. rapa, réalisent à la méiose de 1.8 à 3,4 fois plus de crossing-overs que les hybrides tétraploïdes (AACC), issus du croisement entre colza et colza synthétique (B. rapa (AA) xB. Oleracea (CC)), et 6,1 fois plus de crossing-overs que l espèce diploïde B. rapa.Interspecific hybridization between plant related species is a good way to realise introgressino of genes, in order to increase the genetic variability of cultivated species. Genetic recombinations between genomes of the crossed species are needed to optimise introgressions. This study aims to determine the factors that act on recombination rates in crosses between the allotetraploid species B. napus (AACC, 2n=38), and one of its progenitors, B. rapa (AA, 2n=20), and is based on the study of introgression of resistance genes to Leptosphaeria maculans into B. napus. After having identified three specific resistance genes in B. rapa, I tested the effect of three factors on recombination rates between A genomes of B. rapa and B. napus, by the comparison of the rates obtained in different crosses. I detected no effect of the divergence between A genomes of B. rapa and B. napus, but significant effects of both the B. napus genotype and the structure of F& hybrids. The effet of the hybrid structure was considerable : at the meiosis of AAC triploid hybnrids, resulting from crosses between B. napus and B. rapa, recombination rates were from 1.8 to 3.4 fold higher than in AACC tetrploid hybrids, resulting from crosses between B. napus and a reysnthesized B. napus (B. rapa (AA) x B. oleracea (CC)), and 6.1 fold higher than in the diploid B. rapa species.RENNES-Agrocampus-CRD (352382323) / SudocSudocFranceF

Contrôle génétique de la recombinaison homéologue chez les hapoloïdes de Colza (Brassica Napus L.)

Valoriser les gènes d intérêt présents au sein des espèces sauvages apparentées aux espèces cultivées et/ou exploiter le polymorphisme structural susceptible d exister au seuil des génomes polyploïdes implique de mieux comprendre quels sont les facteurs génétiques et structuraux contrôlant les échanges entre les génomes apparentés (homéologues) et comment ils inter-agissent. Pour répondre à ces questions, j ai développé une stratégie originale permettant d analyser la fréquence et la nature des remanimements structuraux qui surviennent au court de la méiose de plantes haploïdes (Ac, n=19) de colza (Brassicas Napus) présentant des comportements métiotiques très contrastés. J ai d abord montré que les gamètes fonctionnels produit par un haploïde de colza sont très majoritairement des gamètes non-réduits de type FDR, que ces gamètes transmettent pratiquement l intégralité des réarrangements structuraux générés au cours de la méiose et que la plupart de ces remaniements résultent de crossing-overs qui se réalisent de façon privilégiée entre les régions homéologues, mais qui peuvent également se former entre des régions para(homéo)logues. J ai alors montré que les différences de comportement méiotique observées entre génotypes haploïdes en Metaphase I reflètent des différences de fréquence de recombinaison. J ai observé que les remaniements effectuent différemment les génomes A et C, ce qui suggère qu il pourrait y avoir une sélection contre certains d entre eux. J ai enfin montré que la fréquence de remaniements varie d un groupe de liaison à l autre (cela dépend du génotype haploïde) et en fonction de la position sur les groupes de liaison.Natural biodiversity and beneficial chromosome rearrangements are an under exploited sustainable resource that can be used to enrich the genetic basis of cultivated plants. A lot is still to be done to make a more efficient use of these vast reservoirs of variation. This process is related to meiosis and recombination between related but divergent genomes. In this study, I have genotyped progenies of haploid x euploid B. napus with molecular markers and analysed the rate and nature of chromosomal rearrangements originating at meiosis in two haploid genotype (n=19) that display very different meiotic behaviour at metaphase I. I show that a high number of chromosomal rearrangements occur during meiosis of B. napus haploid and are transmitted by FDR-like unreduced gametes to their progeny ; most of these rearrangements are produced by crossing-overs that occur preferentially between regions of primary homeology (Muller), but may also take place between other duplicated regions showing intragenomic or intergenomic homology. I show that the two haloid genotypes display sharp differences of meiotic homeologous recombination and that the two genomes of B. napus are differentially affected by rearrangements, which suggests that some rearrangements are counter-selected. Finally I show that the rate of chromosomal reshuffling varies within and among chromosomes.RENNES-Agrocampus-CRD (352382323) / SudocSudocFranceF

Effects of temperature on R1m6-mediated resistance to Leptosphaeria maculans in Brassica napus

Near-isogenic lines of Brassica napus lines with/without the resistance gene Rlm6 were used to investigate the effects of temperature on Rlm6-mediated resistance to Leptosphaeria maculans. Leaves were inoculated with ascospores of L. maculans carrying the corresponding avirulence gene AvrLm6. Inoculated plants were incubated at 15°C or 25°C. DarmorMX (with Rlm6) was resistant to L. maculans at 15°C but susceptible at 25°C, and Darmor (without Rlm6) was susceptible at both temperatures. On Darmor, large grey leaf lesions developed at both 15 and 25°C. On DarmorMX, small dark necrotic spots were produced at 15°C but large grey lesions were produced at 25°C. The incubation period of L. maculans (from inoculation to the appearance of first lesion) was longer on DarmorMX than on Darmor. The infection efficiency (number of lesions resulting from inoculation with 100 ascospores) was greater on Darmor than on DarmorMX at 15 and 25°C. Further characterisation of the Rlm6-mediated resistance showed that the resistance was effective at 25°C if inoculated plants were pre-incubated at 15°C for 5 days before moving them to 25°C, but not if inoculated plants were pre-incubated at 15°C for only 2 days before moving them to 25°C. We conclude that temperature affects Rlm6-mediated resistance to L. maculans in B. napus leaves

Towards a durable management of genetic resistances to

Blackeg is the major disease of winter oilseed rape in France. For an efficient control of the disease several tools could be combined, but mainly plant breeding has been used to increase winter oilseed rape resistance to blackleg. A useful step was reached in the nineties, using a specific resistance gene (Rlm1). After being widely used this resistance was broken down by an increase of the virulent sub-populations of the fungus. Such a situation worried the different actors and raised the question of the promotion of a durable management of genetic resistances to Leptosphaeria. After a synthetic presentation of the state of the art in the fields of genetics of resistance, of Leptosphaeria populations and on agronomic practices able to control the pathogen, the promotion of a durable management of resistances is discussed. This target needs to precise the strategy, to improve methodologies to characterise genotypes, to promote proper agronomic practices, to follow Leptosphaeria population behaviour and to motivate economic actors

Towards a durable management of genetic resistances to Leptosphaeria maculans

Blackeg is the major disease of winter oilseed rape in France. For an efficient control of the disease several tools could be combined, but mainly plant breeding has been used to increase winter oilseed rape resistance to blackleg. A useful step was reached in the nineties, using a specific resistance gene (Rlm1). After being widely used this resistance was broken down by an increase of the virulent sub-populations of the fungus. Such a situation worried the different actors and raised the question of the promotion of a durable management of genetic resistances to Leptosphaeria. After a synthetic presentation of the state of the art in the fields of genetics of resistance, of Leptosphaeria populations and on agronomic practices able to control the pathogen, the promotion of a durable management of resistances is discussed. This target needs to precise the strategy, to improve methodologies to characterise genotypes, to promote proper agronomic practices, to follow Leptosphaeria population behaviour and to motivate economic actors

Towards a durable management of genetic resistances to Leptosphaeria maculans

Blackeg is the major disease of winter oilseed rape in France. For an efficient control of the disease several tools could be combined, but mainly plant breeding has been used to increase winter oilseed rape resistance to blackleg. A useful step was reached in the nineties, using a specific resistance gene (Rlm1). After being widely used this resistance was broken down by an increase of the virulent sub-populations of the fungus. Such a situation worried the different actors and raised the question of the promotion of a durable management of genetic resistances to Leptosphaeria. After a synthetic presentation of the state of the art in the fields of genetics of resistance, of Leptosphaeria populations and on agronomic practices able to control the pathogen, the promotion of a durable management of resistances is discussed. This target needs to precise the strategy, to improve methodologies to characterise genotypes, to promote proper agronomic practices, to follow Leptosphaeria population behaviour and to motivate economic actors

Towards a durable management of genetic resistances to Leptosphaeria maculans

Blackeg is the major disease of winter oilseed rape in France. For an efficient control of the disease several tools could be combined, but mainly plant breeding has been used to increase winter oilseed rape resistance to blackleg. A useful step was reached in the nineties, using a specific resistance gene (Rlm1). After being widely used this resistance was broken down by an increase of the virulent sub-populations of the fungus. Such a situation worried the different actors and raised the question of the promotion of a durable management of genetic resistances to Leptosphaeria. After a synthetic presentation of the state of the art in the fields of genetics of resistance, of Leptosphaeria populations and on agronomic practices able to control the pathogen, the promotion of a durable management of resistances is discussed. This target needs to precise the strategy, to improve methodologies to characterise genotypes, to promote proper agronomic practices, to follow Leptosphaeria population behaviour and to motivate economic actors