Molecular genetic analysis of plant Mei2-like genes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at Massey University, Palmerston North, New Zealand
Molecular and genetic methods were used to analyse how a novel class of genes, plant Mei2-like genes may be involved in the regulation of morphogenesis in plants. The study specifically aimed to 1) further characterise maize te1 (the first plant Mei2-like gene to be genetically analysed) and understand the morphological basis of the te1 mutant phenotype and 2) analyse the function of Arabidopsis Terminal Ear Like (TEL) genes using expression analyses and reverse genetics strategy. te1 maize mutants are initially characterised by abnormal phytomer formation and development. A more detailed morphological analysis shows that mutant plants 1) have smaller vegetative shoot apices than the wild type, 2) initiate leaves at a higher, more distal position on the apical dome and 3) have higher plastochron ratio. Molecular analyses of kn1 expression pattern, a marker of leaf founder identity, show that dowregulation of kn1 transcripts occur higher up the dome. Clonal analyses show that fewer number of leaf founder cells are recruited to form the leaf. TEL1 and TEL2 are expressed in distinct overlapping domains in the undifferentiated region of the shoot apical meristems during the embryo, vegetative and reproductive stages of Arabidopsis development suggesting involvement of these genes in regulating meristem development and subsequent maintenance. The distinct expression of TEL1 in both the embryonic SAM and RAM raises the possibility of a unifying regulatory mechanism in the formation of the root and the shoot. The absence of TEL single knockout phenotypes supports the idea of functional redundancy. When the TEL genes were both knocked out, double mutant phenotypes show apical-basal pattern defects, ectopic production of numerous secondary shoots, production of numerous leaves and basic embryonic pattern defects such as deletions of apical and/or basal region of the seedling. Results of this study support the hypothesis that plant Mei2-like genes are important in regulating morphogenesis in plants and that they are required in the early patterning of the basic plant body.