Desenvolvimento de marcadores moleculares EST-SSRs e mapeamento funcional em cana-de-açucar (Saccharum spp.) / Development of EST-SSR molecular markers and functional mapping in sugarcane

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Sugarcane (Saccharum spp.) is one of the most important cash crops, highly contributing towards the production of raw sugar and bioethanol produced worldwide. Even though Brazil is the major producer, sugar yield is considered low. Breeding programs for the attainment of new improved sugarcane varieties, which are more productive and more resistant to plagues and illnesses, could be sped up with the development of genetic markers that are PCR-specific and strongly linked to genes that control the desired agronomic traits. The use of genetic markers in genetic mapping and QTL (Quantitative Trait Loci) studies has allowed important progress in the knowledge of the genomic structure and genetics of sugarcane. It is a known fact that the ESTs (Expressed Sequence Tags) have great potential to be used with such purposes. The Sugarcane Expressed Sequence Tag Project (SUCEST) has identified about 43000 clusters that represent the sugarcane genes with a potential to be used in the development of genetic markers. In this context, the objective of the present work was to develop and map EST-SSR markers in a progeny obtained by the cross between two pre-commercial sugarcane varieties, complementing the genetic mapping programs of this population. A search in the SUCEST database resulted on the identification of the microssatellites or SSR (Single sequence repeats) markers in 2005 clusters. Thus, three hundred and seventy two EST-SSR loci had been developed and analyzed and, out of these, 149 were selected for mapping analyses. A total of 2303 polymorphic markers (SSRs, EST-SSRs, RFLPs, EST-RFLPs and AFLPs) were identified among the 100 F1 individuals, of which 1669 (72.5%) were single dose (SD ? segregated 1:1 and 3:1) markers. Map analyses were carried out using JoinMap (version 3.0) and OneMap algorithm, based on a single-dose marker approach. The linkage relationships of simplex markers were determined at a LOD score threshold of 5 and a recombination fraction threshold of 0.35 and map distances were derived from the recombination fraction using the Kosambi function. Out of these 1669 SD markers, 664 (40%) were scattered onto 192 co-segregation groups (CGs) with a total estimated map length of 6261.1 cM. Using both genomic and EST-derived SSR and RFLP, 120 of the 192 CGs were formed into fourteen putative homology groups (HGs). One hundred and thirteen of the 149 EST-SSRs evaluated were mapped and presented homology to previously studied genes of other species. The addition of the EST-derived markers increased the coverage and density of the previous map of this population, which also enabled the construction of the first functional linkage sugarcane map. The EST-SSRs developed have the potential to be used in the detection of QTLs associated to important economic traits for sugarcane culture.

ASSUNTO(S)

polyploidy sugar-cane marcadores est-ssr sucest est-ssr markers poliploide cana-de-açucar sucest functional mapping mapeamento funcional

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