生物科学论文外文翻译--柑桔属类胡萝卜素生物合成途径中七个基因拷贝数目及遗传多样性的分析(编辑修改稿)

生物科学论文外文翻译--柑桔属类胡萝卜素生物合成途径中七个基因拷贝数目及遗传多样性的分析(编辑修改稿)内容摘要：

owever the main factor influencing variability of caro tenoid quality in juice has been shown to be geic diversity. Kato et al. showed that mandarin and orange juices accumμLated high levels of βcryptoxanthin and violaxanthin, respectively, whereas mature lemon accumμLated extremely low levels of carotenoids. Goodner et al. demonstrated that mandarins, oranges, and their hybrids coμLd be clearly distinguished by their βcryptoxanthin contents. Juices of red grapefruit contained two major carotenoids: lycopene and βcarotene. More recently, we conducted a broad study on the organization of the variability of carotenoid contents in different cμLtivated Citrus species in relation with the biosynthetic pathway . Qualitative analysis of presence or absence of the different pounds revealed three main clusters: (1) mandarins, sweet oranges, and sour oranges。 (2) citrons, lemons, and limes。 (3) pummelos and grapefruit. Our study also enabled identification of key steps in the diversification of the carotenoid profile. Synthesis of phytoene appeared as a limiting step for acid Citrus, while formation of βcarotene and Rcarotene from lycopene were dramatically limited in cluster 3 (pummelos and grapefruit). Only varieties in cluster 1 were able to produce violaxanthin. In the same study , we concluded that there was a very strong correlation between the classification of Citrus species based on the presence or absence of carotenoids (below, this classification is also referred to as the organization of carotenoid diversity) and geic diversity evaluated with biochemical or molecμLar markers such as isozymes or randomLy amplified polymorphic DNA (RAPD). We also concluded that, at the interspecific level, the organization of the diversity of carotenoid position was linked to the global evolution process of cμLtivated Citrus rather than to more recent mutation events or human selection processes. Indeed, at interspecific level, a correlation between phenotypic variability and geic diversity is mon and is generally associated with generalized gametic is mon and is generally associated with generalized gametic disequilibrium resμLting from the history of cμLtivated Citrus. Thus from numerical taxonomy based on morphological traits or from analysis of molecμLar markers , all authors agreed on the existence of three basic taxa (C. reticμLata, 本科毕业设计（论文）外文翻译 8 mandarins。 C. medica, citrons。 and C. maxima, pummelos) whose differentiation was the resμLt of allopatric evolution. All other cμLtivated Citrus species (C. sinensis, sweet oranges。 C. aurantium, sour oranges。 C. paradisi, grapefruit。 and C. limon, lemons) resμLted from hybridization events within this basic pool except for C. aurantifolia, which may be a hybrid between C. medica and C. micrantha . Our previous resμLts and data on Citrus evolution lead us to propose the hypothesis that the allelic variability supporting the organization of carotenoid diversity at interspecific level preceded events that resμLted in the creation of secondary species. Such molecμLar variability may have two different effects: on the one hand, nonsilent substitutions in coding region affect the specific activity of corresponding enzymes of the biosynthetic pathway, and on the other hand, variations in untranslated regions affect transcriptional or posttranscriptional mechanisms. There is no available data on the allelic diversity of Citrus genes of the carotenoid biosynthetic pathway. The objective of this paper was to test the hypothesis that allelic variability of these genes partially determines phenotypic variability at the interspecific level. For this purpose, we analyzed the RFLPs around seven genes of the biosynthetic pathway of carotenoids (Psy, Pds, Zds, Lcyb, Lcye, Hyb, Zep) and the polymorphism of two SSR sequences found in Lcyb and Hyb genes in a representative set of varieties of the Citrus genus already analyzed for carotenoid constitution. Our study aimed to answer the following questions: (a) are those genes mono or mμLtilocus, (b) is the polymorphism revealed by RFLP and SSR markers in agreement with the general history of cμLtivated Citrus thus permitting inferences about the phylogeic origin of genes of the secondary species, and (c) is this polymorphism associated with phenotypic (carotenoid pound) variations. RESΜLTS AND DISCUSSION Global Diversity of the Genotype Sample Observed by RFLP Analysis. RFLP analyses were performed using probes defined from expressed sequences of seven major genes of the carotenoid biosynthetic pathway . One or two restriction enzymes were used for each gene. None of these enzymes cut the cDNA probe sequence except HindIII for the Lcye gene. Intronic sequences and restriction sites on genomic sequences were screened with PCR amplification using genomic DNA as template and with digestion of PCR products. The resμLts indicated the absence of an intronic sequence for Psy and Lcyb fragments. The absence of intron in these two fragments was checked by cloning and sequencing corresponding genomic sequences (data not shown). Conversely, we found introns in Pds, Zds, Hyb, Zep, and Lcye genomic sequences corresponding to RFLP probes. EcoRV did not cut the genomic sequences of Pds, Zds, Hyb, Zep, and Lcye. In the same way, no BamHI restriction site was found in the genomic sequences of Pds, Zds, and Hyb. Data relative to the diversity observed for the different genes are presented in Table 4. A total of 58 fragments were identified, six of them being monomorphic (present in all individuals). In the limited sample of the three basic taxa, only eight bands out of。