Over the past decade, the free-living flatworm Macrostomum lignano has been successfully used in many areas of biology, including embryology, stem cells, sexual selection, bioadhesion and aging. The increased use of this powerful laboratory model, including the establishment of genomic resources and tools, makes it essential to have a detailed description of the chromosome organization of this species, previously suggested to have a karyotype with 2n = 8 and one pair of large and three pairs of small metacentric chromosomes. We performed cytogenetic analyses for chromosomes of one commonly used inbred line of M. lignano (called DV1) and uncovered unexpected chromosome number variation in the form of aneuploidies of the largest chromosomes. These results prompted us to perform karyotypic studies in individual specimens of this and other lines of M. lignano reared under laboratory conditions, as well as in freshly field-collected specimens from different natural populations. Our analyses revealed a high frequency of aneuploids and in some cases other numerical and structural chromosome abnormalities in laboratory-reared lines of M. lignano, and some cases of aneuploidy were also found in freshly field-collected specimens. Moreover, karyological analyses were performed in specimens of three further species: Macrostomum sp. 8 (a close relative of M. lignano), M. spirale and M. hystrix. Macrostomum sp. 8 showed a karyotype that was similar to that of M. lignano, with tetrasomy for its largest chromosome being the most common karyotype, while the other two species showed a simpler karyotype that is more typical of the genus Macrostomum. These findings suggest that M. lignano and Macrostomum sp. 8 can be used as new models for studying processes of partial genome duplication in genome evolution.

BackgroundVernalization genes VRN1 play a major role in the transition from vegetative to reproductive growth in wheat. In di-, tetra- and hexaploid wheats the presence of a dominant allele of at least one VRN1 gene homologue (Vrn-A1, Vrn-B1, Vrn-G1 or Vrn-D1) determines the spring growth habit. Allelic variation between the Vrn-1 and vrn-1 alleles relies on mutations in the promoter region or the first intron. The origin and variability of the dominant VRN1 alleles, determining the spring growth habit in tetraploid wheat species have been poorly studied.ResultsHere we analyzed the growth habit of 228 tetraploid wheat species accessions and 25 % of them were spring type. We analyzed the promoter and first intron regions of VRN1 genes in 57 spring accessions of tetraploid wheats. The spring growth habit of most studied spring accessions was determined by previously identified dominant alleles of VRN1 genes. Genetic experiments proof the dominant inheritance of Vrn-A1d allele which was widely distributed across the accessions of Triticum dicoccoides. Two novel alleles were discovered and designated as Vrn-A1b.7 and Vrn-B1dic. Vrn-A1b.7 had deletions of 20 bp located 137 bp upstream of the start codon and mutations within the VRN-box when compared to the recessive allele of vrn-A1. So far the Vrn-A1d allele was identified only in spring accessions of the T. dicoccoides and T. turgidum species. Vrn-B1dic was identified in T. dicoccoides IG46225 and had 11 % sequence dissimilarity in comparison to the promoter of vrn-B1. The presence of Vrn-A1b.7 and Vrn-B1dic alleles is a predicted cause of the spring growth habit of studied accessions of tetraploid species. Three spring accessions T. aethiopicum K-19059, T. turanicum K-31693 and T. turgidum cv. Blancal possess recessive alleles of both VRN-A1 and VRN-B1 genes. Further investigations are required to determine the source of spring growth habit of these accessions.ConclusionsNew allelic variants of the VRN-A1 and VRN-B1 genes were identified in spring accessions of tetraploid wheats. The origin and evolution of VRN-A1 alleles in di- and tetraploid wheat species was discussed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0924-z) contains supplementary material, which is available to authorized users.

Contributed by Nikolay P. GoncharovThe review examines the state of knowledge on genes that control the architectonics of wheat plant (spike morphology). It is shown that molecular genetic studies, which have been recently started, allow to find both the orthologous genes from relative species of wheat (barley, rye, etc.) and genes that were not previously used for breeding. Use of these genes for further breeding allows to produce modern wheat commercial cultivars. Key words: spike morphology, plant architecture, gene, wheat species, Triticum. per, we present current knowledge of the agronomically important spike morphology traits in wheat (subtribe Frumentaceae Dum., tribe Triticeae) and explore some of the recent findings in the area of identification of the genes underlying the spike morphology traits. SPIKE MORPHOLOGY TRAITS IN WHEAT SPECIESThe spike is one of the most important parts of a wheat plant. It includes the reproductive organs, produces the seeds, and ensures dispersal of the mature grains. Spike morphology greatly affects breeding, harvest procedures and the yield. Spikes of wheat species differ in several morphological characteristics, including threshability, the presence or absence of awns, spike shape, spike shattering, spike branching and supernumerary spikelets spike (Fig. 1).Threshability. Easy threshing ability is mainly dependent on the tenacity of the glumes covering the grains. The wild species possess hulled grains (syn. non free-threshing), which are covered by a tough glume that remains adhered to the grain after the threshing (Dorofeev and Korovina, 1979). Naked or free-threshing seeds of cultivated wheat species are rounded by soft glumes which release during threshing ( Fig. 1). Wheat varieties with free-threshing seeds appeared during domestication and significantly advanced the efficiency of the threshing process and led to wheat becoming a major crop all over the world (Zhang et al., 2011).The presence or absence of awns. Awns are the threadlike extensions of the lemma. They have photosynthetic function, increase the assimilation of water, and may promote high yield of wheat grown under water-limited conditions (Reynolds and Tuberosa, 2008;Maydup et al., 2010) (Fig. 1). Several comparative studies of the grain yield advantage in awned and awnless lines gave conflicting results. The comprehensive investigation of Rebetzke et al. (2016) showed that awned near-isogenic lines are characterised by slightly greater grain yield due to increased kernel size and reduced screening. It was also demonstrated that awnless wheats with acceptable yield and quality have provide advantage in more favourable environments and future changing climates.In diploid wheat species T. urartu Thum. ex Gandil., T. monococcum, and T. boeoticum Boiss., only awned spikes have been identified to date, but only T. sinskajae A. Filat. et Kurk. has awnless spikes (Dorofeev and Korovina, 1979). Among tetraploid wheat species, all except T. aethiopicum Jakubz. awnless forms were obtained by hybridisation wit...