Selfish supernumerary chromosome reveals its origin
as a mosaic of host genome and organellar sequences
Mihaela Maria Martis, Sonja Klemme, Ali Mohammad Banaei-Moghaddam, Frank R. Blattner, Jií Macas,
Thomas Schmutzer, Uwe Scholz, Heidrun Gundlach, Thomas Wicker, Hana Šimková, Petr Novák, Pavel Neuman,
Marie Kubaláková, Eva Bauer, Grit Haseneyer, Jörg Fuchs, Jaroslav Doležel, Nils Stein, Klaus F. X. Mayera,
and Andreas Houben
Supernumerary B chromosomes are optional additions to the basic set of A chromosomes, and occur in all eukaryotic groups. They differ from the basic complement in morphology, pairing behavior, and inheritance and are not required for normal growth and development. The current view is that B chromosomes are parasitic elements comparable to selfish DNA, like transposons. In contrast to transposons, they are autonomously inherited independent of the host genome and have their own mechanisms of mitotic or meiotic drive. Although B chromosomes were first described a century ago, little is known about their origin and molecular makeup. The widely accepted view is that they are derived from fragments of A
chromosomes and/or generated in response to interspecific hybridization. Through next-generation sequencing of sorted A and B chromosomes, we show that B chromosomes of rye are rich in genederived sequences, allowing us to trace their origin to fragments of A chromosomes, with the largest parts corresponding to rye chromosomes 3R and 7R. Compared with A chromosomes, B chromosomes were also found to accumulate large amounts of specific repeats and insertions of organellar DNA. The origin of rye B chromosomes occurred an estimated ∼1.1–1.3 Mya, overlapping in time with the onset of the genus Secale (1.7 Mya). We propose a comprehensive model of B chromosome evolution, including its origin by recombination of several A chromosomes followed by capturing of additional A-derived and organellar sequences and amplification of B specific repeats.
DEVELOPMENT OF CHROMOSOME-ARM-SPECIFIC MICROSATELLITE MARKERS IN TRITICUM AESTIVUM (POACEAE) USING NGS TECHNOLOGY
XIAOJUN NIE, BIANLI LI, LE WANG, PEIXUN LIU, SIDDANAGOUDA S. BIRADAR, TAO LI, JAROSLAV DOLEŽEL, DAVID EDWARDS, MINGCHENG LUO, AND SONG WEINING
Bread wheat (Triticum aestivum L.) is one of the most important crops worldwide. Availability of its complete genome sequence holds the promise of meeting the challenges of increasing food demand and changing global climate in the 21st century. Wheat is an allohexaploid species (2n = 6x = 42), comprising three homoeologous genomes A, B, and D. It has an estimated genome size of 17 × 109 bp/1C, consisting of more than 90% repetitive sequences. These biological features make genome analysis a huge challenge. To reduce wheat genome complexity, one approach is to dissect the wheat genome into chromosome or chromosome arms using flow cytometric sorting and perform studies at the chromosome-arm level (Doležel et al., 2004). This chromosome-based strategy can simplify wheat genomic analysis to a manageable size and avoid the complexity of working with three homoeologous subgenomes. Furthermore, high-throughput sequencing of isolated single-chromosome-arm DNA was made possible with the advent of next-generation sequencing (NGS) technology, which provides a method to survey the sequence structure, genome
content, and organization of individual chromosomes (Berkman et al., 2012).
