Meiosis and recombination in plants

Date: 

2013 to 2014

Summary: 

The overall goal of the research in my lab is to understand the basis of inheritance in plants by studying the mechanisms of meiosis, particularly pairing of homologous chromosomes and meiotic recombination. Both pairing and recombination are critical for correct segregation of chromosomes into gametes. We want to understand these processes at the molecular level. This basic research will provide a platform for investigations on how meiotic processes can be modified to improve plant breeding methods.

Issue: 

Meiosis is 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 that regulate homologous chromosome pairing and meiotic recombination will lead to identification and characterization of gene networks that regulate these processes. Many proteins are predicted to act in meiosis. Some are unique to meiosis, whereas others are also involved in other cellular processes, such as DNA damage repair and genome maintenance. Consequently, studying meiosis provides insights into the molecular control of many basic cellular processes. Studying meiosis in plants has profound practical application because meiosis and meiotic recombination are 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). Understanding the mechanisms of meiosis is 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.

Response: 

1. Chromosome dynamics in 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. Using this approach, we discovered that maize chromosomes show very dynamic and complex patterns of motility during the prophase of meiosis.
We are now using a genetic approach to examine the role of chromosome motility in meiosis progression. Using live microscopy, we have recently discovered that the pam1 mutant in maize shows dramatically slower chromosome movements compared to wild-type meiocytes. The Pam1 gene has been implicated in the process of formation of the telomere bouquet. Our data suggest that Pam1 and the telomere bouquet are both involved in the dynamic chromosomes movements in prophase I. We are examining defects in the pam1 mutant to understand the effect of chromosome motility on specific meiotic processes, in particular on chromosome homology recognition and pairing.

2. A high-resolution map of meiotic recombination in maize
This is a new project that we are currently developing. The goal of this project is to generate the first sequence-level map of recombination in maize. In maize, as in all other eukaryotes, the position and frequency of recombination events is determined by a two-step process. In the first step, the number and position of sites of meiotic DSBs are selected. In the second step, a subset of the DSBs are selected to be repaired into crossovers. Within the scope of this project, we plan to identify sites where recombination is initiated by formation of meiotic DSBs in chromosomal DNA as well as sites where recombination events are resolved into crossovers. High-resolution genome-wide studies of the distribution of meiotic DSBs, which initiate recombination, and COs have only been conducted so far in budding yeast. In this project, we have adapted techniques successfully used in yeast to examine recombination patterns in maize. Our high-resolution maps will allow understanding of how the distribution of recombination events is related to local genome features, such as the presence of expressed genes, specific DNA sequence motifs, histone modifications, etc. We plan to address several fundamental questions about the pattern of recombination in maize, including:
(i) What is the overall distribution of DSBs along chromosomes?
(ii) Do DSB hotspots overlap with CO hotspots?
(iii) Are DSBs formed in repetitive DNA regions?
(iv) How are DSB and CO frequencies affected by local genome composition, the presence of expressed genes and chromatin modification patterns?
(v) What effects do the internal genome duplications have on recombination frequencies?
(vi) How does non-colinearity of sequences between different maize inbreds affect recombination?
(vii) What is the extent of natural variation in DSB and CO hotspot distribution among maize inbreds?

Impact: 

This is a basic research project. We expect that in the long run this research will contribute to development of new methods for plant breeding and biotechnology. As research on meiosis in model systems is and will continue to be transferable to humans, we also foresee that our findings may contribute to development of new methods to diagnose and treat reproductive disorders in humans, such as infertility.

Submitted by: 

International focus: 

  • United States of America

United States focus: 

  • New York