Tetsuya Endo

Chromosomal breaks occurred in the progeny of a common wheat (Triticum aestivum L. em Thell; 2n = 6x = 42, genome formula AABBDD) cultivar Chinese Spring with a monosomic addition of an alien chromosome from Aegilops cylindrica Host (2n = 4x = 28, CCDD) or A. triuncialls L. (2n = 4x = 28, UUCC) or a chromosomal segment from A. speltoides Tausch (2n = 2x = 14, SS). We identified 436 deletions by C-banding. The deletion chromosomes were transmitted stably to the offspring. We selected deletion homozygotes in the progeny of the deletion heterozygotes and established homozygous lines for about 80% of the deletions. We falled to establish homozygous lines for most of the deletions in the short arm of chromosome 2A and for all deletions in the short arm of chromosome 4B, because plants homozygous for these deletions were sterile. We could not obtain any homozygotes for larger deletions in the long arms of chromosomes 4A, 5A, 5B, and 5D. The deletion stocks showed variations in morphological, physiological, and bichemical traits, depending on the size of their chromosomal deficiency, and are powerful tools for physical mapping of wheat chromosomes.

A standard karyotype based on N-banding, C-banding, and modified C-banding has been constructed for Triticum aestivum L. 'Chinese Spring'. An idiogram and a nomenclature system have been developed for the description of individual bands. Nomenclatural rules have been proposed for the description of chromosomal structural aberrations and polymorphic bands in other wheat cultivars. As a rule each short arm (S) and a long arm (L) consists of a series of dark bands (C-bands) and light bands (mainly euchromatic) and by definition there are no interbands. In some cases, each arm has been subdivided into two or more regions. The description of a band requires designation of a chromosome number, arm (S or L), region, and band. The region number is separated from the band number by a decimal point. Except for arms 1AS, 3AL, 4AS, and 6AS, all wheat chromosome arms have one or more intercalary C-bands and are divisible into three or more bands. It is hoped that the proposed karyotype and nomenclature system will be widely adopted and lay the foundation of definitive chromosome analysis in wheat.Key words: C-banding, N-banding, common wheat, heterochromatin, idiogram.

The satellite sequences (AGGGAG)(n) and Ty3/gypsy-like retrotransposons are known to localize at the barley centromeres. Using a gametocidal system, which induces chromosomal mutations in barley chromosomes added to common wheat, we obtained an isochromosome for the short arm of barley chromosome 7H (7HS) that lacked the barley-specific satellite sequence (AGGGAG)(n). Two telocentric derivatives of the isochromosome arose in the progeny: 7HS* with and 7HS** without the pericentromeric C-band. FISH analysis demonstrated that both telosomes lacked not only the barley-specific centromeric (AGGGAG)(n) repeats and retroelements but also any of the known wheat centromeric tandem repeats, including the 192-bp, 250-bp, and TaiI sequences. Although they lacked these centromeric repeats, 7HS* and 7HS** both showed normal mitotic and meiotic transmission. Translocation of barley centromeric repeats to a wheat chromosome 4A did not generate a dicentric chromosome. Indirect immunostaining revealed that all tested centromere-specific proteins (rice CENH3, maize CENP-C, and putative barley homologues of the yeast kinetochore proteins CBF5 and SKP1) and histone H3 phosphorylated at serines 10 and 28 localized at the centromeric region of 7HS*. We conclude that the barley centromeric repeats are neither sufficient nor obligatory to assemble kinetochores, and we discuss the possible formation of a novel centromere in a barley chromosome.