Differential gene expression in two strains of the endoparasitic wasp Venturia canescens identified by cDNA-amplified fragment length polymorphism analysis

In the endoparasitic wasp Venturia canescens (Hymenoptera: Ichneumonidae) two genetically distinct lines, which differ at the VLP1 gene locus, appear to coexist sympatrically in thelytokous as well as arrhenotokous field and laboratory strains. Both lines display quite distinct morphological, physiological and behavioural variations, such as different oviposition strategies, egg numbers and growth rates during early embryonic development. To examine whether more than one gene is affected in the two lines, we applied cDNA-amplified fragment length polymorphism analysis to examine patterns of gene expression in ovaries of both wasp lines. We show that a number of ovarian transcripts have an altered expression pattern in either line, which was further confirmed by virtual Northern blot analysis. Sequence analysis of the cDNA-amplified fragment length polymorphism fragments revealed that some of the respective genes are expected to be involved in regulation of protein degradation during stress responses and in signal perception/transduction. The full-length sequence of two transcription factors (a homeodomain containing protein and a zinc finger protein) differentially expressed in both lines was obtained by RACE-polymerase chain reaction and their putative role in regulating key developmental processes during embryogenesis is discussed.

Transferable EST-SSR markers for the study of polymorphism and genetic diversity in bread wheat

Nearly 900 SSRs (simple sequence repeats) were identified among 15,000 ESTs (expressed sequence tags) belonging to bread wheat ( Triticum aestivumL.). The SSRs were defined by their minimum length, which ranged from 14 to 21 bp. The maximum length ranged from 24 to 87 bp depending upon the length of the repeat unit itself (1-7 bp). The average density of SSRs was one SSR per 9.2 kb of EST sequence screened. The trinucleotide repeats were the most abundant SSRs detected. As a representative sample, 78 primer pairs were designed, which were also used to screen the dbEST entries for Hordeum vulgare and Triticum tauschii (donor of the D-genome of cultivated wheat) using a cut-off E (expectation) value of 0.01. On the basis of in silico analysis, up to 55.12% of the primer pairs exhibited transferability from Triticum to Hordeum, indicating that the sequences flanking the SSRs are not only conserved within a single genus but also between related genera in Poaceae. Primer pairs for the 78 SSRs were synthesized and used successfully for the study of (1) their transferability to 18 related wild species and five cereal species (barley, oat, rye, rice and maize); and (2) polymorphism between the parents of four mapping populations available with us. A subset of 20 EST-SSR primers was also used to assess genetic diversity in a collection of 52 elite exotic wheat genotypes. This was done with a view to compare their utility relative to other molecular markers (gSSRs, AFLPs, and SAMPL) previously used by us for the same purpose with the same set of 52 bread wheat genotypes. Although only a low level of polymorphism was detected, relative to that observed with genomic SSRs, the study suggested that EST-SSRs can be successfully used for a variety of purposes, and may actually prove superior to SSR markers extracted from genomic libraries for diversity estimation and transferability.