Desynaptic Mutant Research Articles

EMS Induced Desynaptic Male Sterile Lines in Buckwheat (Fagopyrum esculentum Moench)

Cytological analysis of EMS (Ethyl methane sulphonate) treated population of Fagopyrum esculentum revealed an abnormal behaviour of microsporogenesis that affected the meiotic events resulting in the formation of abnormal meiotic products that prevent the gamete formation and impair pollen fertility. The two desynaptic mutants were recorded, showing distinctive variations in the morphology as compared to the control plants. The seeds of Fagopyrum esculentum were treated with EMS solution in different concentrations such as 0.1, 0.3 and 0.5% using potassium phosphate buffer (pH 7) for 5 h. During cytological investigation, 0.5% concentration of EMS enhanced the univalent frequency per cell at diakinesis/Metaphase I, respectively along with unequal segregation at anaphase I which is pronounced to be higher in contrast to bivalents. Because of higher frequency of univalents desynapsis has been categorized as medium-strong type. EMS induced desynaptic plants showed abnormal meiotic behaviour leading to pollen sterility and no seed setting was recorded. The chemical mutagen has acted on recombination genes system which is accountable for synapsis and chiasma formation and further disrupted the complete chiasma assembly. The desynaptic mutant is a potential tool that provides genetic information on the maintenance of chiasma and the study offers the possibility for formation of aneuploids production which may be exploited successfully through chemical mutagenesis in breeding programmes.

Corrigendum

New PhytologistVolume 220, Issue 1 p. 348-348 CorrigendumFree Access Corrigendum This article corrects the following: A spontaneous mutation in MutL-Homolog 3 (HvMLH3) affects synapsis and crossover resolution in the barley desynaptic mutant des10 Isabelle Colas, Malcolm Macaulay, James D. Higgins, Dylan Phillips, Abdellah Barakate, Markus Posch, Susan J. Armstrong, F. Chris H. Franklin, Claire Halpin, Robbie Waugh, Luke Ramsay, Volume 212Issue 3New Phytologist pages: 693-707 First Published online: July 8, 2016 First published: 29 August 2018 https://doi.org/10.1111/nph.15402 Authors for correspondence: Luke Ramsay Tel: +44 844 928 5428 Email: Luke.Ramsay@hutton.ac.uk Robbie Waugh Tel: +44 844 928 5428 Email: Robbie.Waugh@hutton.ac.uk AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat New Phytologist 212 (2016), 693–707, doi: 10.1111/nph.14061 Since its publication, the authors of Colas et al. (2016) have brought to our attention an error in the Acknowledgements section of their article. The correct Acknowledgements is shown below. We apologize to our readers for this mistake. Reference Colas I, Macaulay M, Higgins JD, Phillips D, Barakate A, Posch M, Armstrong SJ, Franklin FCH, Halpin C, Waugh R et al. 2016. A spontaneous mutation in MutL-Homolog 3 (HvMLH3) affects synapsis and crossover resolution in the barley desynaptic mutant des10. New Phytologist 212: 693– 707. Acknowledgements We would like to thank Sybille Mittmann, Amritpal Sandhu and Ruth Perry for technical help. The research leading to these results has received funding from the European Community's Seventh Framework Programme FP7/2007-2013 under grant agreement no. 222883 to R.W., S.J.A. and F.C.H.F. and the ERC project 669182 ‘SHUFFLE’ awarded to R.W. Use of the OMX microscope was supported by the Euro-BioImaging PCS and through the MRC Next Generation Optical Microscopy Award (ref: MR/K015869/1) to I.C., L.R., M.M. and R.W. were funded from the Scottish Government's Rural and Environment Science and Analytical Services Division Work Program 5.2. A.B. and C.H. were funded by the Biotechnology and Biological Science Research Council Grant BB/F020872/1. The authors declare no conflict of interest. Volume220, Issue1October 2018Pages 348-348 ReferencesRelatedInformation

Cytogenetical Study of Induced Desynaptic Variants in <i>Phaseolus vulgaris</i> L.

The cytological screening of gamma ray treated plants revealed few desynaptic plants where an enhanced frequency of univalents were found at metaphase I along with few bivalents. The desynaptic plants were obtained at 200 Gy dose of gamma rays and were characterised as weak and medium strong type. The univalents remained unpaired till later meiotic stages and resulted in the unequal separation of chromosomes at anaphase I. The unequal separation of chromosomes as a consequence of desynapsis lead to the formation of micronuclei and gametes with imbalanced chromosomes, thus affecting the post-meiotic stages also. The desynaptic plants possess very few pods and acquire high pollen inviability. The study suggests the ability of gamma rays in the creation of male sterile lines in Phaseolus vulgaris L. The gamma rays either act on the genes responsible for synapsis and chiasma formation or disrupt the synaptonemal complex affecting chiasmate dissociation. The desynaptic mutants could be used as a potential source for gathering information on chiasma maintenance mechanism as well as to study the genetic mechanism and consequences of male sterility in plants. Further, the male sterile lines could also be profitably utilized in hybridization breeding programmes to produce hybrid seeds.

A spontaneous mutation in MutL-Homolog 3 (HvMLH3) affects synapsis and crossover resolution in the barley desynaptic mutant des10.

Although meiosis is evolutionarily conserved, many of the underlying mechanisms show species-specific differences. These are poorly understood in large genome plant species such as barley (Hordeum vulgare) where meiotic recombination is very heavily skewed to the ends of chromosomes. The characterization of mutant lines can help elucidate how recombination is controlled. We used a combination of genetic segregation analysis, cytogenetics, immunocytology and 3D imaging to genetically map and characterize the barley meiotic mutant DESYNAPTIC 10 (des10). We identified a spontaneous exonic deletion in the orthologue of MutL-Homolog 3 (HvMlh3) as the causal lesion. Compared with wild-type, des10 mutants exhibit reduced recombination and fewer chiasmata, resulting in the loss of obligate crossovers and leading to chromosome mis-segregation. Using 3D structured illumination microscopy (3D-SIM), we observed that normal synapsis progression was also disrupted in des10, a phenotype that was not evident with standard confocal microscopy and that has not been reported with Mlh3 knockout mutants in Arabidopsis. Our data provide new insights on the interplay between synapsis and recombination in barley and highlight the need for detailed studies of meiosis in nonmodel species. This study also confirms the importance of early stages of prophase I for the control of recombination in large genome cereals.

Molecular mapping of five soybean genes involved in male-sterility, female-sterility.

In soybean, asynaptic and desynaptic mutants lead to abnormal meiosis and fertility reduction. Several male-sterile, female-sterile mutants have been identified and studied in soybean, however, some of these mutants have not been mapped to locations on soybean chromosomes. The objectives of this study were to molecularly map five male-sterile, female-sterile genes (st2, st4, st5, st6, and st7) in soybean and compare the map locations of these genes with already mapped sterility genes. Microsatellite markers were used in bulked segregant analyses to locate all five male-sterile, female-sterile genes to soybean chromosomes, and markers from the corresponding chromosomes were used on F2 populations to generate genetic linkage maps. The st2, st4, st5, st6, and st7 genes were located on molecular linkage group (MLG) B1 (chromosome 11), MLG D1a (chromosome 01), MLG F (chromosome 13), MLG B2 (chromosome 14), and D1b (chromosome 02), respectively. The st2, st4, st5, st6, and st7 genes were flanked to 10.3 (∼ 399 kb), 6.3 (∼ 164 kb), 3.9 (∼ 11.8 Mb), 11.0 (∼ 409 kb), and 5.3 cM (∼ 224 kb), and the flanked regions contained 57, 17, 362, 52, and 17 predicted genes, respectively. Future characterization of candidate genes should facilitate identification of the male- and female-fertility genes, which may provide vital insights on structure and function of genes involved in the reproductive pathway in soybean.

Methyl methane sulphonate induced desynaptic mutants in Capsicum annuum L.

Methyl methane sulphonate induced desynaptic mutants in Capsicum annuum L.

The maize (Zea mays) desynaptic (dy) mutation defines a pathway for meiotic chromosome segregation, linking nuclear morphology, telomere distribution and synapsis

Meiosis involves a dramatic reorganization of the genetic material, along with changes in the architecture of the nucleoplasm and cytoplasm. In the opisthokonts, nuclear envelope and meiotic chromosome behavior are coordinated by forces generated in the cytoplasm and transferred to the nucleus by the nuclear-envelope protein linkers SUN and KASH. During meiotic prophase I, the telomere bouquet arrangement has roles in interhomolog recognition, pairing, synapsis, interlock resolution and homologous chromosome recombination. The maize desynaptic (dy) mutant is defective in homologous chromosome synapsis, recombination, telomere-nuclear envelope interactions and chromosome segregation. A detailed three-dimensional cytological analysis of dy revealed telomere misplacement during the bouquet stage, synaptic irregularities, nuclear envelope distortion and chromosome bridges at anaphase I. Using linkage and B-A translocation mapping, we placed dy on the long arm of chromosome 3, genetic bin 3.06. SSR marker analysis narrowed the mapping interval to 9 cM. Candidate genes in this region include a PM3-type SUN domain protein, ZmSUN3. No obvious genetic lesions were found in the ZmSUN3 allele of dy, but a conspicuous splice variant, ZmSUN3-sv1, was observed in mRNA from dy. The variant message is predicted to result in the synthesis of a truncated ZmSUN3 protein lacking two C-terminal transmembrane domains. Other potential candidate genes relevant to the documented phenotypes were also considered. In summary, this study reveals that dy causes disruption of a central meiotic pathway connecting nuclear envelope integrity to telomere localization and synapsis during meiotic prophase.

Spontaneous desynapsis in Corchorus fascicularis Lamk. (Family: Tiliaceae)

A desynaptic mutant of Corchorus fascicularis Lamk. (Family: Tiliaceae) showing distinctive morphological variations than normal was identified from the natural population (1 out of 27 plants scored) of jute species following male meiotic analysis. Self segregation of the desynaptic plant suggested that desynapsis (mutant trait) was monogenic recessive to normal. Compared to normal plants, the spontaneous desynaptic mutant (medium strong type) demonstrated enhanced univalent frequency per cell (4.05, normal-0.31), reduced number of chiasma (6.67, normal- 7.28) and bivalent (5.12, normal- 6.99) per nucleus, few meiocytes (13.64%, normal-5.36%) with unequal separation at AI, cytologically near normal AII (94.83%, normal- 100.00%) cells and high male fertility (81.77%, normal- 92.06%). Cytomixis (prophase I/ metaphase I) was evident in both normal and mutant plants forming aneuploid (mutant: 2n 14-2.80%; normal: 2n14 - 10.22%) PMCs predominantly at MI (mutant: 4.20%, normal: 24.42%) and rarely in AI (mutant: 1.52%, normal: 1.79%) cells.

Induced Desynaptic Male Sterile Lines in Soybean

In a study on soybean using gamma rays, we came across with some sterile mutants. Cytological studies of these mutants clearly revealed desynapsis in them. In these sterile plants only few bivalents and a high frequency of univalents have been recorded and they displayed a very high percentage of pollen sterility. Later meiotic stages were also found to be highly disturbed. The plants were identified as male sterile ones as few pods were formed. It might be possible that gamma rays have acted on some genes responsible for synapsis and chiasma formation and resulted in early chiasmate dissociation suggesting that gamma rays can act as a potential tool in the development of male sterile lines. Study of desynaptic mutants is a potentially important source of information on the chiasma maintenance mechanism. These mutants furthermore can provide useful cytological and genetical informations on the male sterility occured in higher plants.

Strategies for the study of meiosis in rye

We describe how we are furthering our understanding of meiosis in rye (Secale cereale L.) using a combination of cytogenetic and molecular biological approaches. Fluorescent in situ hybridisation, electron microscopy of synaptonemal complexes, sequencing of meiosis-specific genes, and the immunolocalisation of recombinogenic proteins are being combined to build up phenotypic “identikits” of wild type, asynaptic mutants sy1 and sy9, and desynaptic mutant sy10. From this information, we review the status of our current understanding of the genetic control of meiosis in rye, and consider strategies for determining more precisely the interrelationships between meiosis-specific genes and their products.

A new and distinctive male-sterile, female-fertile desynaptic mutant in soybean (Glycine max).

A spontaneous desynaptic mutation, affecting only microsporogenesis and causing pollen sterility, has been detected in BR97-12986H, a line of the official Brazilian soybean breeding program. In this male-sterile, female-fertile mutant, up to metaphase II, the meiotic behavior was similar to that described for the st series of synaptic mutants previously reported in soybean. Besides many univalents, few or total absence of bivalents were recorded in diakinesis. Bivalents presented one or two terminal chiasmata, while univalents retained the sister chromatid cohesion. Bivalents and most univalents congregated at the equatorial metaphase plate, although univalents frequently migrated to the poles prematurely. Laggards resulting from delay in chiasmata terminalization were also recorded. Distinctly different in their behavior from st series soybean mutants, telophase I-originated micronuclei of different sizes organized their own spindle in the second division. This behavior contributed towards an increase in genome fractionation. Several microspores and microcytes of different sizes were recorded at the end of meiosis. Pollen sterility was estimated at 91.2%. Segregation ratio for sterility in this line and its progenies reached 3:1. Allelism tests with st series of synaptic mutants are in progress. The importance of male-sterile, female-fertile mutations for soybean breeding programs is discussed.

Chromosome‐specific desynapsis in the n = 2 race of Haplopappus gracilis (Compositae)

During cytological screening for pollen sterility in a wild population of Haplopappus gracilis (n = 2), several partially sterile plants were found that had good pachytene pairing but varying numbers of univalents. Some plants had chromosome A bivalents or A univalents, while in the same cells chromosome B had only bivalents. In other plants the reverse condition occurred; the B chromosome had B bivalents or B univalents and only A bivalents. This demonstrates a chromosome-specific effect for the desynapsis genes. Hybridization between the two homozygous mutant genotypes produced only normal bivalents; this indicates the two mutants are not alleles and each is recessive. An F2 generation showed independent assortment of the desynaptic mutations. The chromosome A bivalent is the larger of the two and normally has one or two chiasmata; the B bivalent normally has a single chiasma. Chiasmata distribution was tested in the desynaptic mutant A bivalents and showed an acceptable fit to a binomial distribution. This occurs also in heterozygous, asynaptic pairing control gene mutations. Analysis of the NOR bivalent in two hologenomic desynaptic mutations in tomato also showed a good fit to a binomial distribution of chiasmata. This indicates the same methods are applicable to diverse species.

Cytogenetic Studies of Induced Desynaptic Mutants in Barley(Hordeum vulgare L.).

Three induced barley desynaptic mutants DM63, DM92 and DM105 showed varying frequency of univalents and bivalents at MI. The range of univalents per cell was 2-8, 8-14, and 4-8 in these mutants. They exhibited unequal separations and lagging of chromosomes at AI. Multipolar separations and presence of micronuclei in spores were also observed. The mutants were monogenic recessive. ds63 (DM63) was found linked with marker genes V and e in chromosome 2. The recombination values of this gene with marker genes V and e were 40.68±3.74 and 20.71±4.82 respectively. It was mapped in chromosomes 2 in short arm left to marker gene e. Gene ds92 (DM92) was found linked with marker gene trd and B in chromosomes 5 and its recombination values with trd and B were 36.62±3.75 and 24.47±4.17 respectively. This gene was located proximal to B with respect to centromere in long arm of chromosome 1. Gene ds105 (DM105) was found linked with lk2 and n in chromosome 1. The recombination values of this gene with lk2 and n were 36.73±5.41 and 26.78±5.00 respectively. This gene was located in long arm of chromosome 1 in between centromere and marker gene n.

The dsy10 Mutation of Arabidopsis results in desynapsis and a general breakdown in meiosis

The proper pairing and recombination of chromosomes during prophase is essential for the formation of gametes during meiosis. As part of studies to identify genes required for homologous chromosome pairing and recombination during meiosis in plants, we characterized a number of T-DNA-tagged, male-sterile mutants of Arabidopsis. Preliminary cytological studies on one line, 7219 which is male and female sterile, suggested that the mutation may disrupt meiosis and result in the formation of aberrant microsporocytes and microspores. In this report we present the results of a detailed analysis of meiosis in microsporocytes of sterile plants to elucidate the nature of the 7219 mutation. Analysis indicates that the mutation usually results in a desynaptic phenotype, with ten sister chromatids observed prior to metaphase I in most cells. Based on this, we named the mutation dsy10. The presence of several other meiotic defects suggests that dsy10 may not be a typical desynaptic mutant.

Primary Trisomics in Soybean: Origin, Identification, Breeding Behavior, and Use in Linkage Mapping

A primary trisomic is an excellent cytogenetic tool for locating Mendelian genes on a particular chromosome and for associating a conventional genetic linkage group with a specific chromosome. The objectives of this study were to produce and identify 20 primary trisomics of soybean [Glycine max (L.) Merr.] and use them for associating linkage groups with specific chromosomes. Primary trisomics isolated from the progenies of asynaptic and desynaptic mutants, male sterile lines, neutron‐irradiated plants, and tissue culture‐induced sterile mutants were backcrossed (BC4) with soybean cv. Clark 63. They were identified at pachytene on the basis of the diagnostic landmarks such as association of the extra chromosome with its normal homologues in a trivalent configuration, distribution of euchromatin and heterochromatin, total chromosome length, arm ratios, and by examining chromosome pairing at metaphase I in F1 plants with 2n = 42 chromosomes isolated from crosses among primary trisomics. The F1 plants from similar primary trisomics exclusively showed 21 II and those from dissimilar primary trisomics exhibited microsporocytes with 20 II + 2 I, 1 III + 19 II + 1 I, and 2 III + 18 II configurations. Thus, 20 primary trisomics were tentatively identified and were designated as triplo 1 through triplo 20. Female transmission of the extra chromosome in 20 primary trisomics ranged from 27.3% (triplo 20) to 58.5% (triplo 9). On the basis of the modification ratio (17:1) of a gene located on the extra chromosome in primary trisomic analysis, three marker genes Eul (seed urease), Lx1 (lipoxygenase‐1), and P2 (puberulent) were located on chromosomes 5, 13, and 20, respectively. The ultimate aim of this project is to develop by means of primary trisomics a universal cytogenetic map of soybean by associating existing classical and several molecular maps with the specific chromosomes.

Cytology of Induced Desynaptic Mutants in Rice.

Cytology of Induced Desynaptic Mutants in Rice.

Comparative analysis of female and male meiosis in three meiotic mutants of tomato

Female meiosis was analysed in squash preparations of ovules from three meiotic mutants and wild-type plants of tomato. In the completely asynaptic mutant as6, chromosome pairing and chiasma formation were virtually absent in both sexes. In the partially asynaptic mutant asb, with intermediate levels of chromosome pairing at pachytene, there were a higher number of chiasmate chromosome arms in female meiosis than in male meiosis, whereas in the desynaptic mutant as5 there were normal levels of chromosome pairing at pachytene and a similar reduction in chiasma frequency in the two sexes. In wild-type tomato, we found slightly higher numbers of chiasmate chromosome arms in female meiosis than in male meiosis. We propose that the higher female chiasma frequencies in mutant asb and wild-type tomato result from a longer duration of female meiotic prophase. This would allow chromosomes more time to pair and recombine. It is possible that a longer duration of prophase I does not affect mutants as5 and as6, either because the meiotic defect acts before the pairing process begins (in as6) or because it acts at a later stage and involves chiasma maintenance (in as5).

A stably transmitted pair of translocated supernumerary chromosomes in maize

A pair of stably transmitted supernumerary chromosomes of unknown source has been found in a maize stock carrying a desynaptic mutant. The presence of the supernumerary chromosome appears to be unrelated to the meiotic mutant, but is believed to have been derived from a translocated B chromosome contaminant. The supernumerary chromosomes carry a segment of a A chromosome in this stock where there appear to be two normal copies of each of the 10 A chromosomes. Thus, this A chromosome segment is present in quadruplicate. Surprisingly, a quadrivalent configuration is formed in most microsporocytes, which involves not only synapsis but also chiasma formation in the A chromosome segments involved in the quadrivalent. This represents a strong preferential pairing of supernumeraries with the normal A chromosome segments. Such nonrandom association and crossing over might provide information on the nature of early homologue alignment at meiosis.

Evidence from a maize desynaptic mutant points to a probable role of synaptonemal complex central region components in provision for subsequent chiasma maintenance.

Homozygotes for the dsy1 desynaptic mutant of maize show massive failure of chiasma maintenance during diplotene and diakinesis. Although some chiasmata persist until anaphase I in most microsporocytes expressing this mutant, homozygotes are completely or nearly completely sterile, owing apparently to disjunctive irregularities. Pachytene synaptic errors and some synaptic failure also are found, but recombination nodules are common in homologously synapsed regions, and equational separation of a heterozygous knob into univalents or open arms at diakinesis clearly demonstrates that chiasma failure occurs following crossing-over. A wider than normal synaptonemal complex central region and uniform apparent weakness of central region cross connections to spreading procedures strongly suggest the presence of a genetic lesion in a synaptonemal complex central region component. The dsy1 mutant may provide an especially important source of material for molecular studies on the nature of chiasma maintenance mechanism.

Microsporogenesis in three tetraploid somatic hybrids of potato and their di(ha)ploid fusion partners

The microsporogenesis of three somatic hybrids of potato, i.e. one tetraploid Solanum tuberosum (+) S. phureja, one tetraploid and one hypertetraploid S. tuberosum (+) desynaptic mutant, has been examined and compared with the microsporogenesis of the di(ha) ploid fusion partners. The somatic hybrids had a first meiotic division with uni-, bi-, and multivalents like that of tetraploid potatoes, illustrating introgression and dominance over desynapsis. Abnormal spindle orientations at second meiotic division, sporad types with reduced and unreduced cells and viable pollen occurred at various frequencies. Pollen fertility could not be predicted on the basis of pollen fertility of the fusion partners. Pollen sterility was partially due to abnormal chromosome numbers. Only the tetraploid S. tuberosum (+) desynaptic mutant produced normal amounts of viable seeds.