Analysis of leaf development and KNOTTED1-like homeobox (KNOX) function in Arabidopsis and maize

The aim of this work has been to investigate the function of KNOTTED1-like homeobox (KNOX) genes in both Arabidopsis and maize. The analysis of KNOX genes in a misexpression context has allowed investigation of both the function of the KNOX pathway and its effects on leaf development. The regulation of KNOX gene expression is central to the transition from meristem to leaf identity in many plant species. Loss of function mutations in the KNOX genes KNOTTED1 (KN1) and SHOOTMERISTEMLESS (STM), in maize and Arabidopsis respectively, result in a failure to maintain a shoot apical meristem (SAM). This suggests that the expression of KNOX genes in the SAM is required for the maintenance of a functional meristem. Ectopic expression of KNOX genes in the leaves of both maize and Arabidopsis affects the elaboration of normal leaf morphology by conferring less determinate characters to the leaf.; During the time of my thesis, an approach taken by a number of investigators to isolate upstream regulators of the KNOX pathway was to identify recessive mutations that phenocopy KNOX misexpression phenotypes. This led to the identification of ROUGH SHEATH2 and ASYMMETRIC LEAVES1 that encode MYB proteins that negatively regulate KNOX gene expression in the leaves of maize and Arabidopsis, respectively. In this work I have identified a novel mutation in maize that phenocopies aspects of KNOX misexpression but acts independently of the KNOX pathway. I have also utilized KNOX misexpression phenotypes to identify downstream components that mediate KNOX function in Arabidopsis.; The dominant mutant Wab1 appears to phenocopy the effects of dominant Knox mutations on proximo-distal patterning of the maize leaf. Characterization of early leaf development, however, shows that Wab1 affects specification of pattern in both the proximo-distal and medio-lateral axes of the leaf in a manner independent of knox function. Genetic analysis suggests that Wab1 affects specification of a lateral domain that lies immediately internal to the margin domain defined by narrowsheath1 (ns1) and ns2. liguless1 is misexpressed early in Wab1 leaf development and compensates for the effect of Wab1 outside of this domain.; Evidence suggests that the gibberellin (GA) pathway acts downstream of KNOX gene function in Arabidopsis. A reduction in GA signaling or biosynthesis promotes KNOX-dependent ectopic meristematic activity in Arabidopsis leaves. (Abstract shortened by UMI.)...