Source: CORNELL UNIVERSITY submitted to
MEIOSIS AND MEIOTIC RECOMBINATION IN PLANTS
Sponsoring Institution
State Agricultural Experiment Station
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0202508
Grant No.
(N/A)
Project No.
NYC-149306
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Nov 1, 2004
Project End Date
Oct 31, 2009
Grant Year
(N/A)
Project Director
Pawlowski, W. P.
Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853
Performing Department
PLANT BREEDING
Non Technical Summary
The objective of this project is to understand the mechanisms of meiosis, a specialized type of cell division leading to the production of gametes. Each plant cell contains two copies of each chromosome, one from the mother and the other from the father. During early stages of meiosis, these two chromosome copies find each other, pair, and exchange parts. These processes are of major importance as meiosis is the basis of genetics and plant breeding. Results from studying meiosis in plants are also transferable to other organisms, including humans, where meiosis failures have profound consequences, leading to aneuploidy, spontaneous abortions, birth defects, and infertility. The mechanisms by which chromosomes identify their appropriate partners and efficiently exchange their parts during meiosis are not well understood. We aim to identify and study these mechanisms by identifying genes that play key roles in these processes and understanding their function.
Animal Health Component
5%
Research Effort Categories
Basic
95%
Applied
5%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2012499108025%
2062499103025%
2062499104025%
2062499108025%
Goals / Objectives
The objective of this project is to understand the mechanisms regulating meiosis. Meiosis is a specialized type of cell division that leads to the production of gametes. It is essential for accurate transmission of genetic material from parents to the progeny and for genetic recombination, which is pivotal for generating genetic variation and is the basis of plant breeding. During early stages of meiosis, chromatin in the nucleus undergoes a dramatic reorganization. At the same time, double-strand breaks are generated on chromosomes, initiating meiotic recombination. Subsequently, the double-strand breaks are repaired, leading to crossing over. Concurrently with recombination, homologous chromosomes recognize each other, pair, and synapse. We are interested in understanding all aspects of meiosis and finding ways with which this knowledge can be utilized for crop improvement. Of our particular interest is understanding the mechanisms of homologous chromosome pairing and recombination. The project combines genomic, proteomic, and classical genetic approaches to identify meiotic genes that affect chromosome pairing and recombination with cutting-edge microscopy to study functions of these genes. We use several plant model systems, including maize and rice, two of the world's most important crops, as well as Arabidopsis thaliana. Our long-term goals are to elucidate: (1) what is the mechanism of homologous chromosome pairing, (2) what is the relationship between pairing and the chromosome homology search and recombination, and (3) how are paring, recombination, and synapsis coordinated. The springboard to studying meiotic chromosome pairing is the cloning and characterization of the poor homologous synapsis 1 (phs1) gene in maize. This gene is required for proper pairing of homologous chromosomes in early stages of meiosis. In the absence of the phs1 products, chromosomes cannot identify their proper homologs and associate with non-homologous partners. phs1 mutants in maize also exhibit recombination defects. Our detailed analysis of the phs1 gene function indicates that this gene is involved in the coordination between meiotic chromosome pairing and recombination. In the short term we plan to: 1. Study the mechanism by which PHS1 promotes homologous pairing in meiosis. 2. Study and clone other maize genes with mutant phenotypes similar to phs1. 3. Identify more genes and pathways that are involved in chromosome pairing and the homology search in maize, rice, and Arabidopsis. 4. Identify genes in plants that play key roles in the process of meiotic recombination. We will use a reverse genetic approach by studying plant homologs of known recombination genes from other species. We will also take a forward genetic approach by QTL mapping genes responsible for variations in the recombination level in plants. 5. We will study whether the frequency of meiotic recombination in plants may be improved by enhancing meiotic pathways that lead to crossing-over events at the expense of crossovers.
Project Methods
To study meiosis, we will combine a variety of experimental approaches, including classical genetics, genomics, and proteomics, combined with cell biology methods, including state-of-the-art microscopy. We will: 1. Use forward genetics to identify new meiotic genes. We will generate mutant populations and perform mutant screens in maize, rice, and Arabidopsis, as well as screen existing mutant populations for meiotic mutants. 2. Use reverse genetics to study functions of meiotic genes. We will generate and identify knock-outs in meiotic genes using RNAi approaches and transposon tagging. We will also produce specific point mutations using TILLING. 3. Study meiotic mutants using three-dimensional deconvolution microscopy. 4. Study genetic networks regulating meiosis with proteomic and genomic methods.

Progress 11/01/04 to 10/31/09

Outputs
OUTPUTS: Meiosis is a specialized cell division, essential for accurate transmission of genetic material from parents to the progeny. Consequently, it is one of the most fundamental processes in all sexually reproducing organisms. Our research on the mechanisms regulating chromosome behavior in meiosis will lead to identification and characterization of gene networks that regulate these processes. Studying meiosis in plants has profound practical application because meiosis is one of the main sources of genetic diversity in plants, which is the basis of plant breeding. Meiosis research in plants will also contribute to the development of methods for homologous gene replacement and improved genetic transformation, allowing manipulation of meiotic recombination levels, and acquiring apomixis (embryo development without fertilization). 1. Understanding mechanism of homologous chromosome pairing in plants. The goal of this project is to understand the mechanisms of homology recognition and homologous chromosome pairing in meiosis in plants. Homologous pairing is critical for correct segregation of chromosomes into gametes. However, pairing is one of the most poorly understood meiotic processes. We identified a unique class of meiotic mutants in maize, containing the previously characterized poor homologous synapsis1 (phs1) and two new mutants desynapticCS (dsyCS), and segregationII (segII), in which homologous pairing is replaced by associations between non-homologous chromosomes. The progression of recombination is also disrupted and meiotic DNA double-strand breaks (DSBs) are not properly repaired. To understand how these genes regulate the events of meiotic prophase, we are conducting detailed analyses of the effect of the phs1, dsyCS, and segII mutations on the progression of pairing, synapsis, and recombination at the molecular level. We hypothesize that genes defined by these mutants control a novel step in meiotic prophase, which involves coordination between chromosome pairing and recombination. 2. Live imaging of meiotic prophase in maize and the role of the Pam1 gene. Early stages of meiotic prophase I are a period of dramatic reorganization of chromosomes in the nucleus, which includes their spatial repositioning. Until now, this process in plants could only be studied in fixed cells because isolated plant prophase I meiocytes cannot be cultured in vitro. We developed a system to observe meiosis in intact live anthers, which, in contrast to isolated meiocytes, can be cultured over a period of several days. Meiocytes are imaged using multiphoton excitation microscopy, which allows observing cells located several tissue layers deep from the surface. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
discovered that the PHS1 protein acts in the cytoplasm and regulates the progression of both recombination and chromosome pairing by controlling the import into the nucleus of two key recombination proteins, RAD50 and MRE11. RAD50 and MRE11 are components of the MRN protein complex that processes meiotic double-stand breaks to produce single-stranded DNA ends, which act in the homology search and recombination. We found that PHS1 plays the same role in homologous pairing in both Arabidopsis and maize, whose genomes differ dramatically in size and repetitive element content. This suggests that PHS1 affects pairing of the gene-rich fraction of the genome rather than preventing pairing between repetitive DNA elements. We propose that PHS1 is part of a novel system that regulates the progression of meiotic prophase by controlling entry of meiotic proteins into the nucleus. 2. Chromosome dynamics in meiotic prophase in maize and the role of the Pam1 gene. Using live imagine, we discovered that maize chromosomes show very dynamic and complex patterns of motility in zygotene in pachytene, which include rapid movements of individual chromosome segments as well as rotations of the entire chromatin in the nucleus. We found that chromosome motility was coincident with dynamic deformations of the nuclear envelope. The complexity of the nuclear movements implies that several different mechanisms affect chromosome motility in early meiotic prophase in maize. We propose that the vigorous nuclear motility provides a mechanism for homologous loci to find each other during zygotene.

Publications

  • Sheehan M.J., Pawlowski W.P. 2009. Live imaging of rapid chromosome movements in meiotic prophase I in maize. PNAS 106: 20989-94.
  • Pawlowski W.P., Cande W.Z. 2005. Coordinating the events of the meiotic prophase. Trends in Cell Biology 15: 674-681.
  • Ronceret R., Doutriaux M.P., Golubovskaya I.N., Pawlowski W.P. 2009. PHS1 regulates meiotic recombination and homologous chromosome pairing by controlling the transport of RAD50 to the nucleus. PNAS 106: 20121-6.
  • Pawlowski W.P., Wang C.-J.R., Golubovskaya I.N., Szymaniak J.M., Shi L., Hamant O., Zhu, T., Harper, L., Sheridan W.F., Cande W.Z.. 2009. Maize AMEIOTIC1 is essential for multiple early meiotic processes and likely required for the initiation of meiosis. PNAS 106: 3603-8.
  • Pawlowski W.P., Sheehan M.J., Ronceret R. 2007. In the beginning: the initiation of meiosis. BioEssays 29:511-514. Ronceret A., Bozza C.G., Pawlowski W.P. 2007. Naughty behavior of maize minichromosomes in meiosis. Plant Cell 19: 3835-3837.


Progress 10/01/07 to 09/30/08

Outputs
OUTPUTS: 1. Understanding mechanism of homologous chromosome pairing in plants. The goal of this project is to understand the mechanisms of homology recognition and homologous chromosome pairing in meiosis in plants. Homologous pairing is critical for correct segregation of chromosomes into gametes. However, pairing is one of the most poorly understood meiotic processes. We identified a unique class of meiotic mutants in maize, containing the previously characterized poor homologous synapsis1 (phs1) and two new mutants desynapticCS (dsyCS), and segregationII (segII) in which homologous pairing is replaced by associations between non-homologous chromosomes. The progression of recombination is also disrupted and meiotic DNA double-strand breaks (DSBs) are not properly repaired. To understand how these genes regulate the events of meiotic prophase, we are conducting detailed analyses of the effect of the phs1, dsyCS, and segII mutations on the progression of pairing, synapsis, and recombination at the molecular level. We hypothesize that genes defined by these mutants control a novel step in meiotic prophase, which involves coordination between chromosome pairing and recombination. 2. Live imaging of meiotic prophase in maize and the role of the Pam1 gene. Early stages of meiotic prophase I are a period of dramatic reorganization of chromosomes in the nucleus, which includes their spatial repositioning. Until now, this process in plants could only be studied in fixed cells because isolated plant prophase I meiocytes cannot be cultured in vitro. We have developed a system to observe meiosis in intact live anthers, which, in contrast to isolated meiocytes, can be cultured over a period of several days. Meiocytes are imaged using multiphoton excitation microscopy, which allows observing cells located several tissue layers deep from the surface. In a second part of this project, we aim to elucidate the role of the maize Pam1 gene in chromosome dynamics during prophase I. Pam1 has been implicated in the process of formation of the telomere bouquet, a cytological structure comprised of telomeres of all chromosomes clustering on a single site of the nuclear envelope. The bouquet forms in late leptotene and persists until early pachytene. It is hypothesized that the role of the bouquet is to facilitate chromosome pairing by pre-aligning chromosomes and confining them to a smaller volume inside the nucleus. In collaboration with Syngenta, we are positionally cloning the Pam1 gene. To our knowledge, this will be the first bouquet gene cloned de novo in any higher eukaryote. PARTICIPANTS: Arnaud Ronceret Moira Sheehan Christopher Bozza Gagan Sidhu Brandon Lemesh Patricia Eliasinski Emily Pinto Peter Mattingly TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
1. Understanding mechanism of homologous chromosome pairing in plants. We discovered that the PHS1 protein acts in the cytoplasm and controls import into the nucleus of a recombination protein RAD50. RAD50 is a nuclease that functions in processing of meiotic DSBs before they are repaired. We also found that the dsyCS, segII, and phs1 mutants show different chromosome pairing dynamics even though all three mutations lead to non-homologous chromosome associations. 2. Live imaging of meiotic prophase in maize and the role of the Pam1 gene. Using the live imaging technique, we discovered that maize chromosomes show very dynamic and complex patterns of motility mostly in zygotene but also in pachytene, which include (i) rapid movements of small chromosome segments, (ii) extensive motility of entire chromosomes, and (iii) oscillations of entire nuclei. Thanks to the superb cytology of maize, we can trace chromosome landmarks such as telomeres and centromeres to measure their speed and the distance they travel. Using this approach, we discovered that the rapid chromosome motility in zygotene and pachytene is driven by the movements of the telomeres. We also found that chromosome movements in the pam1 mutant are much slower than in wild-type meiocytes, suggesting that the Pam1 gene and the bouquet are both involved in the dynamic chromosomes movements in prophase I.

Publications

  • Pawlowski* W.P., Wang C.-J.R., Golubovskaya I.N., Szymaniak J.M., Shi L., Hamant O., Zhu, T., Harper, L., Sheridan W.F., Cande* W.Z. (* corresponding authors). Initiation of meiosis in maize by AM1. PNAS. 2009
  • Bozza C.G., Pawlowski W.P. 2008. The cytogenetics of homologous chromosome pairing in meiosis in plants. Cytogenetic and Genome Research 120: 313-319. Ronceret R., Sheehan M.J., Pawlowski W.P. 2008. Chromosome dynamics in meiosis. In: Cell Division Control in Plants (D.P.S. Verma and Z. Hong, eds.). Springer-Verlag, Heidelberg. pp. 103-124.
  • Esch*, E., Szymaniak, J.M., Yates, H., Pawlowski*, W.P., Buckler*, E.S. (* corresponding authors). 2007. Using crossover breakpoints in recombinant inbred lines to identify quantitative trait loci controlling the global recombination frequency. Genetics 177: 1851-1858.
  • Ronceret A., Bozza C.G., Pawlowski W.P. 2007. Naughty behavior of maize minichromosomes in meiosis. Plant Cell 19: 3835-3837.


Progress 10/01/06 to 09/30/07

Outputs
OUTPUTS: The first goal of this project is to understand the mechanisms of homology recognition in homologous chromosome pairing in meiosis in plants. Homologous pairing is critical for correct segregation of chromosomes into gametes. However, pairing one of the most poorly understood meiotic processes. We recently identified a unique class of meiotic genes in maize, containing Poor homologous synapsis1 (Phs1), DesynapticCS (DsyCS), and SegregationII (SegII). We hypothesize that these genes control a novel step in chromosome pairing. In mutants of these genes, homologous pairing is replaced by associations between non-homologous chromosomes. The progression of recombination is also disrupted, as meiotic DNA double-strand breaks (DSBs) are not properly repaired, indicating that these three genes also control the coordination between chromosome pairing and recombination. The phenotypes of these mutants are unique among meiotic mutants in any model organism to date. We propose to use this novel mutant class to unravel the mechanism of chromosome pairing in meiosis. Detailed analyses of the effect of the phs1, dsyCS, and segII mutations on the progression of pairing, synapsis, and recombination at the molecular level are conducted to understand how these genes regulate the events of meiotic prophase. Additional tests will determine if the three genes act in the same meiotic pathway. We are also in the process of cloning DsyCS and SegII to facilitate further understanding of their roles in meiosis. In addition, we are conducting experiments to better understand the role of the PHS1 protein in meiosis by identifying when and where the protein functions in the meiotic prophase as well as identifying proteins that interact with PHS1. The second part of the project is to elucidate the role of telomere clustering (the bouquet) in chromosome pairing in maize. It is hypothesized that the bouquet facilitates chromosome pairing by pre-aligning chromosomes prior to pairing. However, its exact role in meiosis remains unknown. Most research on the bouquet is conducted in yeast but none of the yeast proteins involved in bouquet formation have homologs in plants or any other higher eukaryotes. Maize is an excellent system to study the bouquet and the maize pam1 mutant is the only known bouquet mutant outside of yeast. We are using pam1 to study the function of the bouquet. This research combines three-dimensional microscopy, fluorescent in situ hybridization (FISH), with immunolocalization of key meiotic proteins to study the behavior of chromosomes in the absence of the bouquet in pam1 mutants. In collaboration with Syngenta, we are positionally cloning the pam1 gene. To our knowledge, this will be the first bouquet gene cloned de novo in any higher eukaryote. We will also use maize-Tripsacum hybrids to test the hypothesis that incompatibilities in bouquet formation are responsible for some cases of sterility defects observed in inter-specific crosses. PARTICIPANTS: Postdoctoral associates: Arnaud Ronceret, Moira Sheehan. Ph.D. students: Christopher Bozza, Gagan Sidhu.

Impacts
(i) We identified that DsyCS and SegII, together with the previously characterized Phs1, form a new class of meiotic genes. We hypothesize that these three genes together control a novel step in homologous chromosome pairing. At the same time, we discovered that DsyCS, SegII, and Phs1 affect the meiotic recombination pathway in different ways, suggesting that each gene has a different mode of action. While in the phs1 mutant, meiotic recombination is arrested in its early stages, in the dsyCS and segII mutants some recombination intermediates continue on to form crossovers and chiasmata. In dsyCS, some of these crossover events take place between non-homologous chromosomes, while in segII only homologous chromosomes recombine. Our efforts now focus on studying interactions of these three genes. (ii) We generated segregating maize populations to clone the DsyCS and SegII genes. Cloning these two genes in underway. (iii) We generated and characterized transgenic maize plants expressing a tagged version of the PHS1 protein, which are now being used to identify PHS1-interacting proteins with a proteomics approach. (iv) We developed and tested a set of fluorescent in situ hybridization (FISH) probes that will be used to monitor chromosome dynamics using three-dimensional microscopy. This will be a helpful tool to investigate chromosome behavior with regards to the formation of the telomere bouquet. (v) We mapped the pam1 gene to the center of bin 5 on maize chromosome 1. In summer 2007, we generated and screened a large population to fine-map the gene. Positional cloning of pam1 is in progress.

Publications

  • Ronceret, R., Sheehan, M.J., Pawlowski, W.P. 2007. Chromosome segregation during mitosis and meiosis. In: Cell Division Control in Plants. (D.P.S. Verma and Z. Hong, eds.). Springer-Verlag, Heidelberg. (Invited book chapter, in press).
  • Pawlowski, W.P., Sheehan, M.J., Ronceret, R. 2007. In the beginning: the initiation of meiosis. BioEssays 29:511-514. (Invited review).
  • Bozza C.G., Pawlowski W.P. 2007. dsyCS and segII define a novel class of homologous pairing mutants. Maize Genetics Conference. Chicago, IL.
  • Ronceret A., Pawlowski W.P. 2007. Analysis of the molecular role of PHS1 in meiotic chromosome pairing. Maize Genetics Conference. Chicago, IL.
  • Sheehan M.J., Golubovskaya I.N., Pawlowski W.P. 2007. Using the maize plural abnormalities of meiosis1 (pam1) mutant to dissect the role of the telomere bouquet in pairing and recombination. Maize Genetics Conference. Chicago, IL.


Progress 01/01/06 to 12/31/06

Outputs
Goals: The goal of this project is to understand the basis of inheritance in plants by studying the mechanisms of meiosis, particularly pairing of homologous chromosomes and meiotic recombination. 1. Understanding the mechanism of homologous chromosome pairing. The springboard to this research is the Poor homologous synapsis 1 (Phs1) gene in maize. Phs1 is required for proper pairing of homologous chromosomes in meiosis. We are conducting experiments to better understand the role of the PHS1 protein in meiosis by identifying when and where the protein functions in the meiotic prophase as well as identifying proteins that interact with PHS1. In 2006, we generated and characterized transgenic maize lines expressing a tagged version of the PHS1 protein. We are now utilizing these lines to purify the putative PHS1-containing protein complex. In addition, we are studying two other maize meiotic genes DesynapticCS (DsyCS) and SegregationII (SegII), which are also involved in regulating homologous chromosome pairing. Based on analyses of recombination and chromosome pairing defects in the dsyCS and segII mutants in maize, we identified that DsyCS and SegII form, together with Phs1, a novel class of meiotic genes that play key roles in homologous pairing. Our efforts will now focus on studying interactions of these genes. In 2006 we also generated segregating maize populations to clone the DsyCS and SegII genes. Cloning of the two genes is now underway. 2. The telomere bouquet in maize and its role in meiotic chromosome pairing and genome stabilization in hybrids. This part of the project aims to elucidate the role of telomere clustering (the bouquet) in chromosome pairing in maize. It is hypothesized that the bouquet facilitates chromosome pairing by pre-aligning chromosomes prior to pairing. However, its exact role in meiosis remains unknown. Most research on the bouquet is conducted in yeast but none of the yeast proteins involved in bouquet formation have homologs in plants or any other higher eukaryotes. Maize is an excellent system to study the bouquet and the maize pam1 mutant is the only known bouquet mutant outside of yeast. We are using pam1 to study the function of the bouquet. We will also use maize - Tripsacum hybrids to test the hypothesis that incompatibilities in bouquet formation are responsible for some cases of sterility defects observed in inter-specific crosses. 3. Natural variation in meiotic recombination in maize. The goal of this objective is to survey diversity in the rates of meiotic recombination and sequence of key recombination proteins. Evidence exists that substantial genetically controlled within-species variation in meiotic recombination rates exists in maize as well as in other species. We want to survey this variation and identify its sources. In 2006, we focused our efforts in this part of the project on developing molecular tools to efficiently measure meiotic recombination rates.

Impacts
Meiosis is essential for accurate transmission of genetic material from parents to the progeny. In plants, meiosis is a major source of new genetic variation, on which plant breeders apply selection. Our research will lead to identification of genes and genetic mechanisms that regulate key processes of meiosis, homology recognition and homologous chromosome pairing, and meiotic recombination. Studying meiosis in plants has many important implications for plant breeding and agriculture, such as development of methods for homologous gene replacement and improved genetic transformation, and acquiring apomixis (embryo development without fertilization). Plant breeders could use strains with increased recombination lines to reduce linkage drag during introgression of traits form unimproved genetic backgrounds, to obtain recombinants representing new desirable combinations of genes, use smaller breeding populations, and accelerate the breeding cycle. Understanding the mechanisms of meiosis is also a central problem of medical genetics because meiotic errors in humans result in infertility and formation of aneuploid gametes. Aneuploidy is the primary genetic cause of pregnancy loss and the most common cause of mental retardation if the fetus survives to term. A number of genetic diseases, such as Bloom's syndrome, are caused by uncontrolled levels of recombination.

Publications

  • No publications reported this period


Progress 01/01/05 to 12/31/05

Outputs
Goals: We study meiosis in plants, particularly pairing of homologous chromosomes and meiotic recombination. Our main goal is to understand the mechanisms regulating these processes at the molecular level. The springboard to this research is the poor homologous synapsis 1 (phs1) gene in maize that the PI has recently cloned. phs1 is required for proper pairing of homologous chromosomes in meiosis. In is absence, chromosomes associaste with non-hopmologous partners in meiotic prophase I, instead of their proper homologs. To better understand the role of the PHS1 protein, we are: (1) characterizing the protein itself (behavior during meiosis, functions of conserved domains, and role in regulating the progression of meiotic recombination), and (2) identifying other meiotic proteins that interact with PHS1. In a separate study, we identified two meiotic mutants in maize, desynapticCS (dsyCS) and segregationII (segII), which may represent genes involved in the same step of chromosome pairing as phs1. We will characterize these mutants and clone the corresponding genes. Accomplishments: 1. Understanding the role of the PHS1 protein in homologous chromosome pairing in meiosis. In the past year, we initiated experiments to identify proteins that interact with PHS1. We generated recombinant E. coli stains expressing a PHS1 fusion protein and produced the protein in bacteria. The E. coli-expressed PHS1 is now used to produce anti-PHS1 antibodies in rats. We also generated a construct to expressed the PHS1 protein tagged with the TAP tag in transgenic maize plants. These resources will be used in a proteomic approach to identify proteins that interact with PHS1. 2. Characterizing dsyCS and segII maize meiotic mutants. Our preliminary description of the dsyCS and segII mutant phenotypes indicated that they both show severe defects in meiotic metaphase I, manifested by the presence of a large number of univalents. In 2005, we used fluorescent in situ hybridization (FISH) to demonstrate that these two mutants show high percentage of non-homologous chromosome associations that replace normal homologous pairing. In segII, we found that 75 percent of bivalents were formed between non-homologous chromosomes, while in dsyCS all chromosome associations were non-homologous. These phenotypes are very similar to the phenotype of the phs1 mutant and indicate that dsyCS and segII, together with phs1, define a novel class of genes controlling homologous chromosome pairing. We are pursuing cloning the dsyCS and segII genes. In 2005, we generated cloning populations for both genes and collected tissue samples for DNA extractions.

Impacts
Meiosis is essential for accurate transmission of genetic material from parents to the progeny. While much has been learned during the past two decades about the mechanisms of meiotic recombination and chromosome synapsis, homologous chromosome pairing remains the least understood process in meiosis. Our research will lead to the identification of genes and genetic mechanisms that regulate homology recognition and chromosome pairing. Studying meiosis in plants has many important implications for plant breeding and agriculture, such as development of methods for homologous gene replacement and improved genetic transformation, allowing manipulation of meiotic recombination levels, and acquiring apomixis (embryo development without fertilization). Understanding the mechanisms of meiosis is also a central problem of medical genetics because meiotic errors in humans result in infertility and formation of aneuploid gametes. Aneuploidy is the primary genetic cause of pregnancy loss and the most common cause of mental retardation if the fetus survives to term.

Publications

  • Pawlowski W.P. and Cande W.Z. 2005. Coordinating the events of the meiotic prophase. Trends in Cell Biology. 15:674-681.