Key messageUnreduced gametes.AbstractThe absence of a strict pachytene checkpoint in plants presents an opportunity to study meiosis in polyhaploid organisms. In the present study, we demonstrate that meiosis is coordinated in hybrids between disomic wheat–rye substitution lines 1Rv(1A), 2R(2D), 5R(5D), 6R(6A) and rye (Triticum aestivum L. × Secale cereale L., 4x = 28, ABDR). By using in situ hybridization with a centromere pAet6-09 probe and immunostaining with H3Ser10ph-, CENH3-, and α-tubulin-specific antibodies, we distinguished four chromosome behaviour types. The first one is a mitotic-like division that is characterized by mitotic centromere architecture, robust bipolar spindle, one-step loss of arm and centromere cohesion, and sister chromatid separation in the first and only meiotic division. The second type involves a monopolar spindle formation, which appears as a hat-shaped group of chromosomes moving in one direction, wherein MT bundles are co-oriented polewards. It prevents chromosome segregation in meiosis I, with a bipolar spindle distributing sister chromatids to the poles in meiosis II. These events subsequently result in the formation of unreduced microspores. The other two meiotic-like chromosome segregation patterns known as reductional and equational plus reductional represent stand-alone types of cell division rather than intermediate steps of meiosis I. Only sterile pollen is produced as a result of such meiotic-like chromosome behaviours. Slightly variable meiotic phenotypes are reproducibly observed in hybrids under different growth conditions. The 2R(2D)xR genotype tends to promote reductional division. In contrast, the genotypes 1Rv(1A)xR, 5R(5D)xR, and 6R(6A)xR promote equational chromosome segregation and monopolar spindle formation in addition to reductional and equational plus reductional division types.Electronic supplementary materialThe online version of this article (doi:10.1007/s00497-016-0279-5) contains supplementary material, which is available to authorized users.
The development of bread wheat introgressions with alien genetic material from cultural and wild Triticeae species is an effective method for expanding the wheat gene pool necessary for breeding. To date, numerous collections of introgressions as substitutions and chromosome modifications have been obtained; however, the creation and study of wheat with new valuable traits still remain an important line of research. Rye Secale cereale L., whose chromosomes carry genes that control valuable economic and biological characteristics and properties, is widely used to produce new wheat forms. In this study, a wheat-rye translocation obtained by backcrossing the wheat-rye disomic-substitution line 2R(2D)1 with the variety Novosibirskaya 67 was characterized. The chromosomal composition of karyotypes was studied using fluorescent in situ hybridization and C-banding. Two centric translocations, derived from two long arms of chromosomes 2D and 2R, T2DL.2RL, were identified, the remaining 40 wheat chromosomes did not undergo modifications. Meiosis in the lines was stable. Chromosomes T2DL.2RL formed bivalents in all meiocytes, which confirmed their homology. The morphological characteristics of the spike in the T2DL.2RL line and Novosibirskaya 67 did not differ. A comparative analysis of productivity between the T2DL.2RL translocation line and the parental forms, Novosibirskaya 67 and the 2R(2D)1 line, was carried out. The T2DL.2RL line is inferior to Novosibirskaya 67 in all characters with different confidence levels. The productivity characters of the 2R(2D)1 line exceeded or did not differ from those of T2DL.2RL, however, the mass of 1000 grains was significantly lower. The results showed the effect of the T2DL.2RL translocation on the trait “plant height”. This character was significantly lower than that of Novosibirskaya 67 in two vegetation periods. Consequently, the T2DL.2RL translocation reduces plant height and productivity.
To date, few data have been accumulated on the contribution of meiotic restitution to the formation of Triticum aestivum hybrid karyotypes. In this study, based on FISH and C-banding, karyotype reorganization was observed in three groups of F5 wheat–rye hybrids 1R(1A) × R. Aberrations, including aneuploidy, telocentrics, and Robertsonian translocations, were detected in all groups. Some of the Group 1 plants and all of the Group 2 plants only had a 4R4R pair (in addition to 1R1R), which was either added or substituted for its homeolog in ABD subgenomes. In about 82% of meiocytes, 4R4R formed bivalents, which indicates its competitiveness. The rest of the Group 1 plants had 2R and 7R chromosomes in addition to 1R1R. Group 3 retained all their rye chromosomes, with a small aneuploidy on the wheat chromosomes. A feature of the meiosis in the Group 3 plants was asynchronous cell division and omission of the second division. Diploid gametes did not form because of the significant disturbances during gametogenesis. As a result, the frequency of occurrence of the formed dyads was negatively correlated (r = −0.73) with the seed sets. Thus, meiotic restitution in the 8n triticale does not contribute to fertility or increased ploidy in subsequent generations.
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