FUNCTIONAL ANALYSIS OF GENES REQUIRED FOR MEIOSIS IN ARABIDOPSIS

Open Access
Author:
Li, Wuxing
Graduate Program:
Plant Physiology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
September 14, 2005
Committee Members:
  • Timothy W Mcnellis, Committee Member
  • Richard Cyr, Committee Member
  • Teh Hui Kao, Committee Member
  • Hong Ma, Committee Chair
Keywords:
  • recombination
  • meiosis
  • Arabidopsis
  • synapsis
  • pairing
  • solo dancers
  • atrad51
  • atrad51c
Abstract:
Meiotic prophase I is a long and complex phase. Interactions between homologs during meiotic prophase I, such as recombination and synapsis, are required for proper chromosome segregation. Although mutant studies have revealed a number of genes required for recombination and synapsis, few genes have been identified in Arabidopsis. Here I describe the mutant analysis of three Arabidopsis genes that are essential for recombination and synapsis in Arabidopsis: SOLO DANCERS; AtRAD51; and AtRAD51C. The solo dancers (sds) mutant was obtained from a collection of Ds-transposon insertional mutants and mutant plants exhibit severe defects in homolog synapsis, recombination and bivalent formation during meiotic prophase I, subsequently resulting in seemingly random chromosome distribution and formation of abnormal meiotic products. Sequence and protein interaction analyses indicate that SDS encodes a novel cyclin (Azumi et al., EMBO J, 2002), arguing strongly that homolog interaction during meiotic prophase I requires a novel meiosis-specific cyclin in Arabidopsis. Because mutation in AtSPO11-1 causes similar abnormal meiosis, we hypothesized that AtSPO11-1 might be one of the downstream or interacting components of the SDS protein. To test this hypothesis, expression of AtSPO11-1 in sds was characterized and meiosis in the sds atspo11-1 double mutant was analyzed. The results indicate that AtSPO11-1 expression is not blocked in sds, and double mutant analysis of sds syn1, sds ask1, and sds atrad51-1 suggests that AtSPO11-1 retains its function in Double stranded DNA breaks (DSB) formation in the sds mutant. In addition to the mutant characterization of sds, I analyzed the T-DNA insertional mutants for the other two genes, AtRAD51 and AtRAD51C. AtRAD51 is an Arabidopsis homolog of yeast and mammalian RAD51, and AtRAD51C is a RAD51 paralog in Arabidopsis. Reverse genetics was applied to analyze the in vivo function of these two genes. Both mutants exhibit normal vegetative and flower development and have no detectable abnormality in mitosis, suggesting these two genes are not necessary for genome integrity under normal conditions. However, both mutants are completely sterile and are defective in both male and female meiosis. During meiotic prophase I, meiotic chromosomes in these two mutants fail to synapse and become extensively fragmented. The severe fragmentation of meiotic chromosomes in these two mutants can be suppressed or partially suppressed by an atspo11-1 mutation, suggesting that the fragmentation phenotype largely represents a defect in processing DSBs generated by AtSPO11-1. Analysis using electron microscopy of meiosis in these two mutants indicates that atrad51-1 exhibits a more severe abnormality in the formation of synaptonemal complexes (SCs), arguing that although both genes are required for processing of DSBs. Furthermore, major aspects of meiotic recombination seem to be conserved between yeast and plants, especially the fact that chromosome pairing and synapsis depend on the function of SPO11 and RAD51 related genes.