A Consensus Map in Cultivated Hexaploid Oat Reveals Conserved Grass Synteny with Substantial Subgenome Rearrangement

Hexaploid oat ( L., 2 = 6 = 42) is a member of the Poaceae family and has a large genome (∼12.5 Gb) containing 21 chromosome pairs from three ancestral genomes. Physical rearrangements among parental genomes have hindered the development of linkage maps in this species. The objective of this work was to develop a single high-density consensus linkage map that is representative of the majority of commonly grown oat varieties. Data from a cDNA-derived single-nucleotide polymorphism (SNP) array and genotyping-by-sequencing (GBS) were collected from the progeny of 12 biparental recombinant inbred line populations derived from 19 parents representing oat germplasm cultivated primarily in North America. Linkage groups from all mapping populations were compared to identify 21 clusters of conserved collinearity. Linkage groups within each cluster were then merged into 21 consensus chromosomes, generating a framework consensus map of 7202 markers spanning 2843 cM. An additional 9678 markers were placed on this map with a lower degree of certainty. Assignment to physical chromosomes with high confidence was made for nine chromosomes. Comparison of homeologous regions among oat chromosomes and matches to orthologous regions of rice ( L.) reveal that the hexaploid oat genome has been highly rearranged relative to its ancestral diploid genomes as a result of frequent translocations among chromosomes. Heterogeneous chromosome rearrangements among populations were also evident, probably accounting for the failure of some linkage groups to match the consensus. This work contributes to a further understanding of the organization and evolution of hexaploid grass genomes

Cytomorphological investigations in Oxyria digyna Hill. from the Kashmir Himalaya, India

In the present paper, detailed cytomorphological investigations in Oxyria digyna Hill. from Kashmir Himalaya—India have been reported for the first time. All the 14 investigated populations of O. digyna are diploid based on x = 7. Out of these in two populations 0–2B chromosomes have been recorded for the first time while 6 populations differed significantly in their meiotic characteristics. Meiotic abnormalities during male meiosis observed include inter PMC chromatin transfer (cytomixis). Non-synchronous disjunction of some bivalents, laggards and bridges at anaphases and telophases. Consequent to these meiotic anomalies, microsporogenesis in meiocytes is abnormal resulting in to dyads, triads and polyads with or without micronuclei. The overall effect is seen in reduced pollen fertility. Unreduced pollen grains were observed in some populations, which differed significantly in their size compared to the normal (reduced) pollen grains. It is observed that a smaller frequency of pollen grains differed morphologically in Aharbal and Yosmarg populations. The remaining eight populations showed regular meiotic course, normal microsporogenesis and high percentage of pollen fertility (95.09–99.09 %).Приводятся детальные цитоморфологические ис-следования Oxyria digyna Hill из Кашмира (Гималаи, Индия). Все 14 изученных популяций являются диплоидными, где x = 7. Из них в двух популяциях впервые описаны 0–2B хромосомы, тогда как шесть популяций сильно различались по своим мейотическим характеристикам. Аномалии мейоза при микроспорогенезе включали цитомиксис, несинхронное расхождение некоторых бивалентов, задержки и мосты в анафазах и телофазах. Возникающий в связи с этим аномальный микроспорогенез приводит к формированию диад, триад и полиад как с микроядрами, так и без них. Общим эффектом является снижение фертильности пыльцы. В некоторых популяциях наблюдали нередуцированные пыльцевые зерна, которые по величине значительно отличались от нормальных. В популяциях Aharbal и Yosmarg некоторые пыльцевые зерна отличались морфологи-чески. Оставшиеся восемь популяций проявляли нормальный ход мейоза, нормальный микроспорогенез и высокий процент фертильности пыльцы (95,09–99,09 %).The authors are grateful to the University Grants Commission, New Delhi for providing financial assistance under the DRS SAP III and DST programmes. Thanks are also due to the Head, Department of Botany, Punjabi University, Patiala for necessary laboratory facilities