Arabidopsis mutants revealing novel aspects of leaf morphogenesis

The establishment of dorsoventrality along the adaxial-abaxial axis is considered an early and crucial step of leaf development and proposed as a requirement for subsequent leaf blade expansion. Because photosynthesis mainly takes place in leaves, several key determinants are required to ensure the proper formation of mature leaves. Several efforts have been dedicated to elucidate the regulatory networks controlling leaf morphogenesis. In this thesis, characterization of novel regulators for both leaf polarity establishment and leaf blade expansion is described. Several Arabidopsis leaf polarity mutants have been identified. However, none of the single, recessive mutants display polarity defects similar to phantastica (phan), the first leaf polarity mutant in Antirrhinum majus. Characterization of filliforme (flr) indicates that flr may be the missing counterpart of phan. flr exhibited the abaxial features in the radialized organs as well as disturbed shoot apical meristem organization. Gene expression analysis revealed the alteration of expression levels of several key regulatory genes. Remarkably, FLR encodes a plastid membrane protein, underlining the roles of plastids in Arabidopsis growth and development. sensitive to red light reduced (srr) 1-2 mutants displayed a narrow-leaf phenotype in addition to defects in light perception and circadian clock regulation. This suggests a connection between leaf blade expansion and the circadian clock. Due to the lack of recognizable functional domains, molecular functions of SRR1 remain unknown. However, genetic interactions between srr1-2 and translational machinery mutants indicate the involvement of SRR1 in the translational regulation of leaf morphogenesis. Previous studies have demonstrated the importance of a translational regulation during leaf morphogenesis in Arabidopsis. Mutations in several ribosomal protein genes similarly result in a pointed-leaf phenotype. Characterization of pointed-first-leaves (pfl) 2-2 mutants, in which the ribosomal protein gene RPS13 is disrupted, revealed perturbation in both adaxial and abaxial mesophyll layers. This mutation in pfl2-2 also significantly enhanced polarity defects in several leaf polarity mutants. These results suggest that RPS13 contributes along with other regulatory genes in establishing or maintaining leaf polarity. Together, genetic approaches present in this dissertation expose unexpected contribution of plastids, the circadian clock and translational machineries on leaf morphogenesis.Ph.D.Includes bibliographical referencesIncludes vitaby Chokchai Kittiwongwattan