New insights on limes and lemons origin from nuclear and cytoplasmic markers genenotyping and targeted nuclear gene sequencing

It is believed that Citrus medica, C. maxima, C. reticulate and C. micrantha have generated all cultivated citrus species. Depending on the classification, lemons and limes are classified either into two species, C. limon and C. aurantifolia (Swingle and Reece, 1967) or into more than 30 (Tanaka, 1977). In order to study the molecular phylogeny of this citrus group, we analyzed 23 targeted sequenced nuclear genes and used three mitochondrial and five chloroplastic markers for 15 lemons and limes compared with representatives of the four basic taxa. We observed three main groups, each one derived from direct interspecific hybridizations: (1) the Mexican lime group (C. aurantifolia), including C. macrophylla, arising from hybridizations between papeda (C. micrantha) and citron (C. medica); (2) the yellow lemon group (C. limon) that are hybrids between sour orange (C. aurantium, which is believed to be a hybrid between C. maxima and C. reticulata) and citron; and (3) a rootstock lemon/lime group (Rough lemon and Rangpur lime) that are hybrids between an acid mandarin and a citron. We also identified different probable backcrosses and genotypes with more complex origin. None of the analyzed limes and lemons shared the C. medica cytoplasm, while this taxon is the common nuclear contributor of all limes and lemons. Limes and lemons appear to be a very complex citrus varietal group with the contribution of the 4 basic taxa. Neither the Swingle and Reece classification nor the Tanaka fit with the genetic evidence. (Résumé d'auteur

Genetic diversity analysis and population structure of the mandarin germplasm revealed by nuclear SNP markers

Citrus reticulata is considered one of the four main ancestral taxa of cultivated citrus and is widely associated with the mandarin horticultural group. However, several studies suggest introgressions of other taxa and the precise structure of the mandarin group is not known. To analyse the structuration of mandarin germplasm and the potential interspecific introgressions, 208 accessions were genotyped by the KASPar method, with sixty-seven single nucleotide polymorphism (SNP) markers mined in 27 nuclear genes and in clementine BAC-ends. These SNP markers were employed for the study of 208 genotypes comprised of 169 'mandarin-like' genotypes and 39 genotypes belonging to ancestral taxa. Structure software was used to identify groups within the mandarin germplasm. Six mandarin groups were identified, some of them in agreement with the species defined by Tanaka. Many mandarins were located between these mandarin groups, indicating a high level of admixture between the identified parental groups. New insights in the organization of mandarin germplasm and its structure are presented in this work, which will be useful for better management of citrus germplasm collections. (Résumé d'auteur

Interspecific and intergeneric somatic hybrids with C. deliciosa Ten. enlights non additive inheritance in allotetraploid citrus

Neoregulation of parental genome expression in allopolyploid plants contributes to the expression of new phenotypes. Somatic hybrids allow combining genomes without sexual recombination and are interesting models to study the immediate effect of allopolyploidisation on the regulation of gene expression and subsequent phenotype elaboration. While most of the citrus germplasm is diploid, somatic hybridization has become an integral part of citrus variety improvement programs aiming to create new allotetraploid rootstocks or to synthesize triploid hybrids by further sexual hybridization. By protoplast fusion CIRAD obtained allotetraploid hybrids between C. deliciosa and 6 others citrus species: 4 belong to Citrus genus (C. limon, lemon; C. aurantifolia, lime; C. sinensis, sweet orange; C. paradisi, grapefruit), 2 belong to Poncirus trifoliata (trifoliate orange) and Fortunella margarita (kumquat). Molecular analysis using 100 SSR markers did not reveal any inconsistency with total addition of parental genomes. Morphological description was done for leaves and fruits as well as the sugar and acid fruit contents. According to the traits and parental combination, codominance or dominance of one parent was observed and lead to conclude for an important contribution of interaction variance in phenotypic diversity elaboration. Analyze by GC-MS of the leaf volatile compounds of the same allotetraploid hybrids revealed a systematic global dominance of the mandarin profile. It was particularly marked regarding the absence of monoterpene aldehydes and monoterpene alcohols and the very low level of sesquiterpene hydrocarbons, sesquiterpene alcohols, and sesquiterpene aldehydes in all hybrids while these compounds were found at high concentrations for the non mandarin parents. 2-D electrophoresis analysis of the leaf proteome of two allotetraploid somatic hybrids combining C. deliciosa with C. aurantifolia and Fortunella margarita displayed a closer relation between the two allotetraploid hybrids and their mandarin parent than with the other parent. Similar results have been observed at transcriptome level in a genome-wide gene expression analysis on fruit pulp of allotetraploid between C. deliciosa and C. limon, using a Citrus 20 K cDNA microarray. The gene expression of the allotetraploid suggested a global dominance of the mandarin fruit pulp transcriptome. Particularly, genes down regulated in mandarin compared to lemon were also repressed in the allotetraploid hybrid. The study is now extended to an interspecific diallelic somatic hybridization scheme to have a wider understanding of genome interaction in allotetraploid citrus. (Texte intégral

Multilocus haplotyping by parallel sequencing to decipher the interspecific mosaic genome structure of cultivated citrus

The most important economic Citrus species originated from natural interspecific hybridization between four ancestral taxa (C. reticulata, C. maxima, C. medica and C. micrantha) with limited further interspecific recombination due to apomixis and vegetative propagation. Such reticulate evolution coupled with vegetative propagation results in genomes that are mosaics of large chromosome fragments of the basic taxa, in frequent interspecific heterozygosity. Breeding of these species is hampered by their complex heterozygous genomic structures. Haplotyping of multiple gene fragments along the genome should be a powerful approach to resolve the evolutionary history of the gene pools, to reveal the admixture genomic structure of current species and to develop innovative breeding schemes. We have analysed the efficiency of parallel sequencing with 454 methodology to decipher the hybrid structure of modern citrus species and cultivars along chromosome 2. Four hundred fifty four amplicon libraries were established with the fluidigm array system for 48 genotypes and 16 gene fragments of chromosome 2. Haplotypes were established from the reads of each accession and phylogenetic analyses were performed from the haplotypic data of each gene fragment. The length of 454 reads and the level of differentiation between the ancestral taxa of modern citrus allowed efficient haplotype phylogenetic assignations for 12 of the 16 gene fragments. The analysis of the mixed genomic structure of modern species and cultivars (i) revealed C. maxima introgressions in modern mandarins; (ii) was consistent with previous hypothesis regarding the origin of secondary species; and (iii) provided a new picture of the evolution of chromosome 2. Perspectives to rebuild the main secondary species from the basic taxa are discussed. (Résumé d'auteur

Genetic structure and phylogeny of the 'true citrus fruit trees' group (Citrinae, Rutaceae)

Despite considerable differences in morphology, the general representing 'true citrus fruit trees' are sexually compatible, but their phylogenetic relationships remain unclear. Most of the important commercial species of Citrus are believed to be of interspecific origin. By studying SNP and indel polymorphisms of 27 nuclear genes on 32 genotypes of Citrus and relatives of Citrus, the phylogenetic relationship between 'true citrus fruit trees' was clarified. Additionally, four mitochondrial (mtDNA) and five chloroplastic (cpDNA) SSRs markers were analysed for the citrus species to specify the maternal phylogeny of Citrus secondary species. A total of 16238 kb of DNA was sequenced for each genotype, and 1156 SNPs and 58 indels were identified. Nuclear phylogenetic analysis revealed that C. reticulata, Poncirus, and Fortunella form a clade that is clearly differentiated from the clade that includes three other basic taxa of cultivated citrus (C. maxima, C. medica and C. micrantha). Clymenia is included in a third strong clade with Eremocitrus and Microcitrus. The nuclear phylogeny of Citrus and its sexually compatible relatives was consistent with the geographic origins of these genera. The origin of Citrus secondary species was analysed both at nuclear and cytoplasmic level and the conclusions mostly agree with previous hypotheses. The SNPs and indels identified at the nuclear level from a relatively large discovery panel will be useful for systematic characterisation of citrus germplasm, both at intra- and inter-specific level. (Résumé d'auteur

Diferencias cualitativas en la forma en que niños y niñas utilizan la imaginación en tareas creativas

En esta comunicación abordamos un tema a menudo controvertido: las diferencias en creatividad en función del sexo de los sujetos. Este estudio fue llevado a cabo con una muestra compuesta por 1277 sujetos, 754 varones y 523 mujeres, 697 niños de entre 9 y 12 años y 580 adolescentes de 13 a 18 años. Para la evaluación de la creatividad se utilizó la Prueba de Imaginación Creativa PIC-N (niños) y PIC-J (adolescentes). Nuestros resultados mostraron que tanto las niñas como las adolescentes obtuvieron mejores puntuaciones en la mayor parte de los índices de creatividad que los niños y chicos de estas edades. Estas diferencias entre sexos fueron mayores en los niños más jóvenes. Estos resultados parecen indicar que existen importantes diferencias cualitativas, más que cuantitativas, en la forma en que niños y niñas utilizan la imaginación en tareas creativas. Consideramos que estas diferencias cualitativas pueden deberse en parte a diferencias biológicas en los ritmos de maduración cerebral de niños y niñas, pero fundamentalmente son debidas a diferencias en los estilos de aprendizaje, las expectativas, y la motivación en el desarrollo de niños y niñas.In this paper, we approach the relationship between two issues which stir up a wide controversy: gender and creativity. The investigation was conducted with a sample of 1277 subjects, 754 males and 523 females: 697 elementary students (9 to 12 years of age) and 580 adolescents (13 to 18 years of age). Our results indicate that in divergent thinking tests females of all ages obtained better results in almost all scores. Greater differences were found in younger children. These results seem to indicate that there are important qualitative, rather than quantitative, differences in the way boys and girls use their imagination in creativity tasks. We consider that these qualitative differences are probably due in part to genetic or biological factors, that might explain the difference between sexes in creative achievement in different domains. But mostly, we believe that these qualitative differences are also due to differences in learning styles, expectations, and motivations, in the development of boys and girls.peerReviewe