University of Western Ontario - Electronic Thesis and Dissertation Repository


Master of Science




Dr. Krzysztof Szczyglowski


Here, I characterize a root-branching hypermorph of Lotus japonicus, called cluster root-like1 (crl1), which originated from a har1-1 suppressor screen. I have shown that the crl1 root phenotype is determined by two independently segregating recessive mutations, har1-1 and Ljamp1-1, with corresponding HAR1 and LjAMP1 encoding an LRR‑receptor-like kinase and a predicted homologue of the Arabidopsis ALTERED MERISTEM PROGRAM 1 protein, respectively. Unlike har1-1, the Ljamp1 mutation does not affect the symbiotic properties of L. japonicus Gifu but exerts a pleiotropic effect on shoot development. Root architecture, however, is regulated by a synergistic action of HAR1 and LjAMP1, as the simultaneous impairment of these two genes results in the determinate root growth phenotype. The steady state levels of several L. japonicus CLE transcripts are shown to be dramatically altered in har1-1 and Ljamp1-1 roots. The corresponding CLE peptides in conjugation with HAR1 and LjAMP1 may be crucial in specifying root architecture.