An in silico analysis of the key genes involved in flavonoid biosynthesis in Citrus sinensis

Citrus species are known by their high content of phenolic compounds, including a wide range of flavonoids. In plants, these compounds are involved in protection against biotic and abiotic stresses, cell structure, UV protection, attraction of pollinators and seed dispersal. In humans, flavonoid consumption has been related to increasing overall health and fighting some important diseases. The goals of this study were to identify expressed sequence tags (EST) in Citrus sinensis (L.) Osbeck corresponding to genes involved in general phenylpropanoid biosynthesis and the key genes involved in the main flavonoids pathways (flavanones, flavones, flavonols, leucoanthocyanidins, anthocyanins and isoflavonoids). A thorough analysis of all related putative genes from the Citrus EST (CitEST) database revealed several interesting aspects associated to these pathways and brought novel information with promising usefulness for both basic and biotechnological applications.

Development and characterization of polymorphic microsatellite markers for the sweet orange ( Citrus sinensis L. Osbeck )

The aims of this study were to develop simple sequence repeat markers (SSRs or microsatellite markers) in citrus and to evaluate the efficiency of these markers for characterization of sweet orange. We developed SSRs from a genomic library of 'Pêra IAC' sweet orange enriched for AG/TC, GT/CA, TCA/AGT and AAC/TTG sequence repeats. We selected 279 sequences from which 171 primer pairs were designed of which 113 with the best banding patterns were selected. Characterization of sweet orange microsatellite loci revealed that AG/TC was the most abundant (69 percent) microsatellite class isolated, followed by GT/CA (15.9 percent), TCA/AGT (8 percent) and AAC/TTG (6.2 percent). The number of alleles ranged from 1 to 4, with a mean of 2 alleles per locus. Four microsatellite loci developed in this study were found to be useful for sweet orange DNA typing. The data obtained from microsatellites loci considered polymorphic will be useful as tools in the selection of zygotic and nucellar plants, identification of seedlings etc. for the cultivars Pêra IAC, Lanceta, Pêra GS 2000, Lamb Summer, Lima, Lima Tardia, Lima Verde, Mimo do Céu, Valência Folha Murcha, Valência Folha Concha, Natal Murcha, Sangüínea and Baía Gigante.

Skewed RAPD markers in linkage maps of Citrus

The objective of this work was to analyze the effects of RAPD markers with skewed segregation on genetic linkage maps. Segregation data for 123 Citrus sinensis (L.) Osbeck cv. Pêra markers and 53 C. reticulata Blanco cv. Cravo markers in F1 progeny composed of 94 hybrids were used. Genetic linkage maps of the two varieties were constructed with non-skewed markers (p < 0.05 and p < 0.01) using the program MAPMAKER 3.0 and a pseudo-testcross strategy. The maps were compared to those constructed with all markers. Alterations in the genetic distances were observed based on the location of the skewed markers within the linkage groups. Generally, the skewed markers were located at the end of the linkage groups, sometimes forming entire linkage groups, without causing significant distance modifications. However, skewed markers located between non-skewed markers caused significant distance modifications and, in some cases, altered the order of the markers. Most of the skewed markers can be included in linkage maps, but in each case the degree of distance modification caused by each marker needs to be assessed.