First karyological report in Larnax and Deprea (Solanaceae)

Somatic chromosomes of 12 samples belonging to seven Larnax Miers species and three Deprea Raf. species are studied. Chromosome number and karyotype analysis of both genera are reported for the first time. All taxa have 2n = 24. The most frequent haploid karyotype formula (8 of 12 samples) is 9 metacentric (m) + 3 submetacentric (sm) chromosomes, whereas L. glabra (Standl.) N.W. Sawyer and Larnax sp. display 10 m + 2 sm. Karyotypes of L. nieva S. Leiva & N.W. Sawyer and D. cuyacensis (N.W. Sawyer & S. Leiva) S. Leiva & Lezama are remarkable for the highest number of sm chromosome pairs, with 7 m + 5 sm and 5 m + 7 sm, respectively, presenting the highest intrachromosomal asymmetry index (A1), whereas Larnax sp. and L. glabra show the lowest A1. Most samples (9 of 12) examined have only one pair of chromosomes with nucleolar organiser regions (NOR), whereas L. glabra, Larnax sp., and D. cuyacensis possess two pairs of NOR. Systematic considerations about the monophyly of Larnax and Deprea are provided. The different karyotype parameters obtained, together with morphological characters, are discussed to single out the species.

Isolation, characterization, and analysis of Leymus-specific DNA sequences

Genomic Southern hybridization using labeled total genomic DNA of Leymus mollis as probe showed intense hybridization signals on all restriction enzyme digested DNA from five species of Leymus Hochst., and four species of Psathyrostachys Nevski. Experiments using the same L. mollis probe, but with unlabeled blocking DNA from Psathyrostachys, showed no hybridization at all. These two genera evidently had the same genomic content. Southern hybridization without blocking allowed identification of DNA fragments abundant in Leymus and Psathyrostachys. Fragments potentially specific to Leymus were cloned. Five repetitive DNA clones from L. mollis and L. arenarius were characterized: pLmIs1, pLmIs44, pLmIs51, pLmIs53, and pLaIs56. These clones hybridized to both Leymus and Psathyrostachys on Southern blots — no clone hybridized to only one of these genera. Both Southern blot and fluorescence in situ hybridization (FISH) experiments showed that all the clones contained dispersed repetitive sequences. They painted all and whole chromosomes uniformly except at centromeres, telomeres, and nucleolar organiser regions. Three of these clones, i.e., pLmIs1, pLmIs44, and pLmIs53, were essentially specific to Leymus and Psathyrostachys — little or no hybridization was detected in other genera such as Triticum, Hordeum, Thinopyrum, or Elymus. Sequence analysis further revealed that the clones were part of retroelements. In particular, the clone pLmIs44 produced hybridization profiles suitable for analysis of genetic relatedness among species. The present study shows that Leymus and Psathyrostachys share the same basic genome, Ns, and therefore provides strong evidence for combining these two genera.Key words: Triticeae, Leymus, Psathyrostachys, genome-specific sequences, retrotransposons.