BackgroundExpressed Sequence Tags (ESTs) are a source of simple sequence repeats (SSRs) that can be used to develop molecular markers for genetic studies. The availability of ESTs for Quercus robur and Quercus petraea provided a unique opportunity to develop microsatellite markers to accelerate research aimed at studying adaptation of these long-lived species to their environment. As a first step toward the construction of a SSR-based linkage map of oak for quantitative trait locus (QTL) mapping, we describe the mining and survey of EST-SSRs as well as a fast and cost-effective approach (bin mapping) to assign these markers to an approximate map position. We also compared the level of polymorphism between genomic and EST-derived SSRs and address the transferability of EST-SSRs in Castanea sativa (chestnut).ResultsA catalogue of 103,000 Sanger ESTs was assembled into 28,024 unigenes from which 18.6% presented one or more SSR motifs. More than 42% of these SSRs corresponded to trinucleotides. Primer pairs were designed for 748 putative unigenes. Overall 37.7% (283) were found to amplify a single polymorphic locus in a reference full-sib pedigree of Quercus robur. The usefulness of these loci for establishing a genetic map was assessed using a bin mapping approach. Bin maps were constructed for the male and female parental tree for which framework linkage maps based on AFLP markers were available. The bin set consisting of 14 highly informative offspring selected based on the number and position of crossover sites. The female and male maps comprised 44 and 37 bins, with an average bin length of 16.5 cM and 20.99 cM, respectively. A total of 256 EST-SSRs were assigned to bins and their map position was further validated by linkage mapping. EST-SSRs were found to be less polymorphic than genomic SSRs, but their transferability rate to chestnut, a phylogenetically related species to oak, was higher.ConclusionWe have generated a bin map for oak comprising 256 EST-SSRs. This resource constitutes a first step toward the establishment of a gene-based map for this genus that will facilitate the dissection of QTLs affecting complex traits of ecological importance.

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Sl'MMAKVGynodioecy is a breeding system consisting of male steriles (MS, females) and hermaphrodites (H), Tbere is how ever within such systems a third, often neglected, class of partially male sterile plants (PMS), i,e, plants with an intermediate sex expression. In tiatural populations of Plantaf;o coronopus, partially male sterile individuals were as common as male steriles (frequencies in tbe range 1'7 36-8",,). These PMS plants constitute a continuous series, linking compk-te male sterility and hermaphroditism. We discovered that temperature influenced sex expression and the degree of male sterilit\ of PMS indi\iduals, but not of AIS and H individuals. Thus, at higher temperatures PMS individuals became more male sterile. Difference in c\ toplasmic background ofthe indi\'iduats did not infiuence their response to temperature. IT is argued tbat partial male sterility is a normal feature of eytiodioecious species and not an abnormality,