FUNCTIONAL AND EVOLUTIONARY ANALYSES OF KINESIN AND MEIOTIC GENES IN PLANTS

Open Access
Author:
Quan, Li
Graduate Program:
Biology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 15, 2008
Committee Members:
  • Hong Ma, Committee Chair
  • Teh Hui Kao, Committee Member
  • Richard Cyr, Committee Member
  • Zhi Chun Lai, Committee Member
Keywords:
  • kinesin
  • meiosis
  • spindle
  • gene duplication
  • homologous recombination
  • functional divergence
Abstract:
Meiosis is an essential step in sexual reproduction but only a small number of genes are known to be needed for plant meiosis. In addition, although several kinesin genes are known to function in intracellular transport and microtubule organization in animal and fungal organisms, relatively little is known about kinesin function in plants. My thesis research focuses on functional studies of kinesin genes in meiosis and other reproductive development, the evolutionary of kinesin genes in plants, and characterization of new meiotic mutants. In the 2nd chapter, two kinesin genes, AtKIN14a and AtKIN14b, which were possibly generated by a recent Arabidopsis genome-wide duplication event, are shown to function redundantly in female meiosis and gametophytic development. Although these two kinesin genes both seem to be under purifying selection, there is evidence for sequence divergence. This might explain the functional difference between these two genes in male meiosis where AtKIN14a plays a more critical role than AtKIN14b since the atkin14b mutant has normal male fertility. This study suggests that these two kinesins might function in microtubule organization during both meiosis and gametophytic mitosis. In the 3rd chapter of this thesis, to understand how plant species are able to have given birth to and retained many copies of kinesin genes through evolution, a genome-wide evolutionary analysis is performed. This analysis indicates that segmental duplication could possibly play a major role in increasing plant kinesin number. Additionally, this analysis suggests that at least in Arabidopsis, these duplicate kinesin pairs have been under purifying selection and exhibit varying ratios of nonsynonymous/synonymous frequencies (dN/dS) across the entire gene length. Moreover, expression analysis of Arabidopsis kinesin genes indicates that most of these pairs show very similar expression profiles during plant development with subtle expression divergence at some stages. This divergence becomes more obvious when plant encounters stressful growth conditions, suggesting potential functional divergence between close paralogs. In the 4th chapter, a forward genetic approach is used to identify genes possibly involved in Arabidopsis meiosis. Two mutants were identified to carry mutational alleles of a known meiotic gene by molecular and genetic analyses. In addition to exhibiting similar homologous recombination defects at late prophase I to the mutant, chromosomal univalents in these two mutant lines are able to be aligned at the equatorial plane. Also, these univalents show stretched chromosomal morphology, suggesting that these chromosomes are under mechanical forces from microtubules. These novel phenotypes suggest that this gene could possibly participate in sister-chromatid recombination, thereby affecting the cohesion and kinetochore orientation.