Spontaneous meiotic mutations of winter rye Secale cereale L. (2n = 14) were revealed in inbred F2 progenies, which were obtained by self-pollination of F1 hybrids resulting from crosses of individual plants of cultivar Vyatka or weedy rye with plants of self-fertile inbred lines. The mutations cause partial or complete sterility, and are maintained in heterozygote condition. Six types of mutations were distinguished as the result of cytological analysis of meiosis and genetic analysis. (1) Plants with nonallelic asynaptic mutations sy1 and sy9 lacked bivalents in 96.8 and 67.0% metaphase I cells, respectively, formed only axial elements but not the mature synaptonemal complex (SC), and had defects in telomere clustering in early prophase I. (2) Weak asynaptic mutant sy3 showed incomplete synapsis at the start of SC degradation at diplotene and lower chiasma number; yet only 2% meiocytes lacked bivalents in MI. (3) Mutations sy2, sy6, sy7, sy8, sy10, and sy19 caused nonhomologous synapsis; i.e., a varying number of univalents and occasional multivalents were observed in MI, which was preceded by switches of pairing partners and fold-back synapsis at mid-prophase I. (4) Mutation mei6 led to the formation of protrusions and minor branched structures of the SC lateral elements. (5) Allelic mutations mei8 and mei8-10 caused irregular chromatin condensation along the chromosome length in prophase I, which was accompanied by chromosome sticking and fragmentation in MI. (6) Allelic mutations mei5 and mei10 determined chromosome supercondensation, caused the disturbance of meiotic spindle assembly, arrested meiosis at various stages but did not affect formation of the pollen wall, thus arrested meiocytes got covered with the pollen wall. Analysis of double mutants revealed recessive epistatic interactions for some mutations; the epistatic group was sy9 > sy1 > sy3 > sy19. This reflects the sequence of meiotic events controlled by the corresponding genes. The expression of sy2 and sy19 proved to be modified by additional genes. Most meiotic mutations found in rye have analogs in other plants.
A novel type of aberration in synaptonemal complex (SC) assembly was found in electron micrographs of surface spread midprophase I nuclei from pollen mother cell preparations of rye. The plants with the mutant phenotype were selected from the fifth- to seventh-generation progenies of an inbred line (Ms6) characterised by partially reduced fertility and known to segregate for the desynaptic mutation sy6. The SC abnormality designated mei6 was at first detected in three sibling plants of the fifth generation of the inbred line. The most striking features were (i) the thorn-like protrusions of the lateral elements (LEs), which were often folded over towards the opposite LE, and (ii) peculiar bars inside the central region of the SC, which were either obliquely or perpendicularly positioned between the LEs. The bars and thorns often coincide with discontinuities in the adjacent LEs, giving rise, in a few cases, to minor branched structures. We analysed 424 surface spread pachytene nuclei obtained from 26 plants selected from the three inbred generations. Bars represented 92% of all abnormalities: their number per cell increased significantly with the progress of meiotic prophase, varying from an average of 1.96 ± 0.39 at midzygotene to 5.16 ± 0.52 at late pachytene and 5.14 ± 0.91 at early diplotene. Our observations suggest that bars are caused by modification and (or) erroneous self-assembly of meiosis-specific proteins intercalating with LE proteins at or near the sites of crossover events. It is also probable that the gene(s) involved is inherited independently from the gene for desynapsis.Key words: Secale cereale, synaptic mutant, meiosis, synaptonemal complex.
A method of in silico search for specific repetitive DNA sequences related to the synaptonemal complex (meiDNA) in mammalian genomes was developed. A study of the distribution of these repeats over chromosomes revealed their scarcity on the Y chromosome and a decrease in recombination frequency in regions enriched in meiDNA. The results are discussed in context of the model of the looplike meiotic chromosome organization during the formation of the synaptonemal complex.
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