UBC Theses and Dissertations
Regulation of stomatal morphogenesis and lateral root development in Arabidopsis thaliana by the leucine-rich repeat receptor-like kinase MUSTACHES Keerthisinghe, Sandra Roshini
Shoot and root systems have evolved numerous specialized structures, including stomata and lateral roots. Stomata, which are essential for mediating gas exchange across the shoot epidermis during photosynthesis, consist of two bilaterally symmetrical guard cells arranged around an epidermal pore. The symmetry displayed by mature stomata is essential for stomatal function. Stomata develop via a dedicated pathway defined by two key divisions, an asymmetric division, and a symmetric division which initiates stomatal bilateral symmetry. The symmetric division is followed by pore and guard cell morphogenesis, which maintains the previously established bilateral symmetry. Lateral roots increase the ability of root systems to acquire nutrients and water from the surrounding environment and lateral root development is also dependent on stage specific divisions. Interestingly, several genes regulating symmetric divisions have also been shown to function in lateral root development. The Leucine-Rich Repeat Receptor-Like Kinase, MUSTACHES (MUS), which belongs to a family of four closely related MUS-LIKE kinases (MUSLs), is required to enforce bilateral symmetry post-symmetric division. Mutants in mus display pore and guard cell morphogenesis defects, as well as defects in microtubule array organization and the polarity of microtubule movement. MUS is expressed in both stomatal lineage and root epidermal cells, suggesting that MUS also functions outside stomatal development. Thus, MUS represents an ideal candidate through which mechanisms influencing pore and guard cell morphogenesis, as well as the impact of post-symmetric division stomatal genes on lateral root development, may be explored. Mutant analysis and time-lapse studies demonstrated that MUS enforces bilateral symmetry by ensuring symmetrical positioning of microtubule organizing centres post-symmetric division. Time lapse studies indicated that microtubule organizing centre delocalization occurred before, and is likely responsible for, the subsequently occurring alterations in microtubule polarity and guard cell morphogenesis defects observed in mus. As well, this work revealed that MUS, the cytoplasmic kinase NIMA-RELATED KINASE 6 and the microtubule associated protein CLIP-170 ASSOCIATED PROTEIN are required for stomatal microtubule organizing centre formation. Additionally, a model where pore placement is regulated by opposing MUS and MUSL1 signaling pathways was developed. Finally, a redundant role for MUS and MUSL1 in lateral root development was confirmed.
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