Identification of ovule and seed genes from Citrus clementina

[EN] Seedlessness is a highly desirable trait in fresh fruit. Citrus varieties, such as Clementine mandarin and other related species, show parthenocarpic fruit development without seeds due to self-incompatibility. In spite of that, these fruits frequently contain seeds as a result of cross-pollination by insects with compatible pollen from other citrus cultivars grown nearby. To solve this problem using a biotechnological approach we aim at the destruction of ovules and/or seeds by directing the expression of a toxic gene using the promoter of an ovule and/or seed specific gene. With the purpose of isolating this kind of genes we constructed two cDNA libraries from ovules and seeds at different developmental stages of the Clementine mandarin (Citrus clementina cv. Clemenules). A total of 1,014 ESTs from the ovule library and 1,042 ESTs from the seed library were generated, with a novelty percentage of 27% and 36% among the Spanish Citrus Functional Genomic Project (CFGP) ESTs database, respectively. Quantitative PCR analysis confirmed nearly specific expression in ovule and/or seed of two genes, TRANSPARENT TESTA16 (CcTT16) and TRANSPARENT TESTA7 (CcTT7). Expression of these two genes is restricted to early seed development, and is localized in the embryo sac and endothelium. The promoters of those genes may be useful to genetically engineer citrus species to avoid seed formation in fruits of commercial varieties.The authors thank Dr. L. Navarro and J. Juarez, from the Instituto Valenciano de Investigaciones Agrarias (Generalitat Valenciana), for the use of the Clementine orchard and Fortune pollen; Dr. J Forment and the Genomics Facility at the IBMCP for sequence analysis and maintenance of to the CFGP database; and Drs. F Tadeo and J Carbonell for critical reading of the manuscript. This work was supported by grants from the Conselleria de Agricultura, Pesca y Alimentacion (Generalitat Valenciana) and Spanish Ministerio de Ciencia y Tecnologia (research grant GEN2001-4885-C05). A.G-L. received a PhD fellowship from the Conselleria de Agricultura, Pesca y Alimentacion.García Lor, A.; Garcia Martinez, JL.; Perez Amador, MA. (2012). Identification of ovule and seed genes from Citrus clementina. Tree Genetics and Genomes. 8(2):227-235. doi:10.1007/s11295-011-0435-xS22723582Al-Shahrour F, Diaz-Uriarte R, Dopazo J (2005) Discovering molecular functions significantly related to phenotypes by combining gene expression data and biological information. Bioinformatics 21:2988–2993Al-Shahrour F, Minguez P, Tarraga J, Montaner D, Alloza E, Vaquerizas JMM, Conde L, Blaschke C, Vera J, Dopazo J (2006) BABELOMICS: a systems biology perspective in the functional annotation of genome-scale experiments. 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Male and female inheritance patterns in tetraploid ‘Moncada’ mandarin

Triploid-breeding programs in citrus are key tool to develop seedless cultivars. Obtaining triploid citrus hybrids may be achieved through different strategies, such as the exploitation of female unreduced gamete in crosses between diploid parents and diploid by tetraploid sexual hybridizations, in which tetraploid genotypes can be used as male or female parents. Genetic configuration of triploid populations from interploid crosses greatly depends on the chromosomic segregation mode of the tetraploid parent used. Here, we have analyzed the inheritance of the tetraploid ‘Moncada’ mandarin and compared the genetic structures of the resulting gametes when used as male and as female parent. The preferential chromosome pairing rate is calculated from the parental heterozygosity restitution (PHR) of codominant molecular markers, indicating the proportion between disomic and tetrasomic segregation. Tetraploid ‘Moncada’ both as female and male parent largely exhibited tetrasomic segregation. However, as female parent, one linkage group (LG8) showed intermediate segregation with tendency towards tetrasomic inheritance, while another linkage group (LG4) evidenced a clear intermediate segregation. On the other hand, when used as male parent two linkage groups (LG5 and LG6) showed values that fit an intermediate inheritance model with tetrasomic tendency. Significant doubled reduction (DR) rates were observed in five linkage groups as female parent, and in six linkage groups as male parent. The new knowledge generated here will serve to define crossing strategies in citrus improvement programs to efficiently obtain new varieties of interest in the global fresh consumption market.EEA ConcordiaFil: Garavello, Miguel Fernando. Instituto Valenciano de Investigaciones Agrarias. Centro de Citricultura y Producción Vegetal; España. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Concordia; ArgentinaFil: Cuenca, José. Instituto Valenciano de Investigaciones Agrarias. Centro de Citricultura y Producción Vegetal; España.Fil: Garcia-Lor, Andrés. Instituto Valenciano de Investigaciones Agrarias. Centro de Citricultura y Producción Vegetal; España.Fil: Ortega, Neus. Instituto Valenciano de Investigaciones Agrarias. Centro de Citricultura y Producción Vegetal; España.Fil: Navarro, Luis. Instituto Valenciano de Investigaciones Agrarias. Centro de Citricultura y Producción Vegetal; España.Fil: Ollitrault, Patrick. Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD). Amélioration Génétique et Adaptation des Plantes (UMR Agap). Unité Mixte de Recherche; FranciaFil: Aleza, Pablo. Instituto Valenciano de Investigaciones Agrarias. Centro de Citricultura y Producción Vegetal; España

Molecular characterization and stress tolerance evaluation of new allotetraploid somatic hybrids between carrizo citrange and Citrus macrophylla W. rootstocks

Polyploidy is one of the main forces that drives the evolution of plants and provides great advantages for breeding. Somatic hybridization by protoplast fusion is used in citrus breeding programs. This method allows combining the whole parental genomes in a single genotype, adding complementary dominant characters, regardless of parental heterozygosity. It also contributes to surpass limitations imposed by reproductive biology and quickly generates progenies that combine the required traits. Two allotetraploid somatic hybrids recovered from the citrus rootstocks—Citrus macrophylla (CM) and Carrizo citrange (CC)—were characterized for morphology, genome composition using molecular markers (SNP, SSR, and InDel), and their tolerance to iron chlorosis, salinity, and Citrus tristeza virus (CTV). Both hybrids combine the whole parental genomes even though the loss of parental alleles was detected in most linkage groups. Mitochondrial genome was inherited from CM in both the hybrids, whereas recombination was observed for chloroplastic genome. Thus, somatic hybrids differ from each other in their genome composition, indicating that losses and rearrangements occurred during the fusion process. Both inherited the tolerance to stem pitting caused by CTV from CC, are tolerant to iron chlorosis such as CM, and have a higher tolerance to salinity than the sensitive CC. These hybrids have potential as improved rootstocks to grow citrus in areas with calcareous and saline soils where CTV is present, such as the Mediterranean region. The provided knowledge on the effects of somatic hybridization on the genome composition, anatomy, and physiology of citrus rootstocks will be key for breeding programs that aim to address current and future needs of the citrus industry