Chromosome constitution of species in the plant genus Chaenomeles

The chromosome number was studied in plants, derived from seeds collected in the wild, of all four species (C. cathayensis, C. japonica, C. speciosa and C. thibetica) presently recognised in the genus Chaenomeles Lindl. (Maloideae, Rosaceae). For the first time the chromosome number of C. thibetica was also determined. Chaenomeles thibetica was diploid and had a chromosome number of 2n = 34. The results of chromosome counting in the three other species were in agreement with the literature. Thus, all species within the genus Chaenomeles were confirmed to be diploid and to have the same chromosome number, 2n = 34

Cassandra retrotransposons carry independently transcribed 5S RNA

We report a group of TRIMs (terminal-repeat retrotransposons in miniature), which are small nonautonomous retrotransposons. These elements, named Cassandra, universally carry conserved 5S RNA sequences and associated RNA polymerase (pol) III promoters and terminators in their long terminal repeats (LTRs). They were found in all vascular plants investigated. Uniquely for LTR retrotransposons, Cassandra produces noncapped, polyadenylated transcripts from the 5S pol III promoter. Capped, read-through transcripts containing Cassandra sequences can also be detected in RNA and in EST databases. The predicted Cassandra RNA 5S secondary structures resemble those for cellular 5S rRNA, with high information content specifically in the pol III promoter region. Genic integration sites are common for Cassandra, an unusual feature for abundant retrotransposons. The 5S in each LTR produces a tandem 5S arrangement with an inter-5S spacing resembling that of cellular 5S. The distribution of 5S genes is very variable in flowering plants and may be partially explained by Cassandra activity. Cassandra thus appears both to have adapted a ubiquitous cellular gene for ribosomal RNA for use as a promoter and to parasitize an as-yet-unidentified group of retrotransposons for the proteins needed in its lifecycle

IRAP and REMAP for retrotransposon-based genotyping and fingerprinting

v2006okBEL/KG