| Summary: | Seed oil, seed coat mucilage and cuticular wax are plant-specific metabolites important for plant development and growth. Therefore, understanding biosynthesis, deposition, transport and regulation of these metabolites will benefit our daily life and the environment. The original objectives of my thesis research were to investigate the regulation of seed oil accumulation by a transcription factor GLABRA2 (GL2; chapter 2) and to explore the secretory process involved in the transport of cuticular waxes from the endoplasmic reticulum to the plasma membrane (chapter 3) in Arabidopsis thaliana. However, my research revealed two unexpected connections between seed oil and seed coat mucilage deposition and between cuticular wax export and cell wall formation.
At the beginning of chapter 2, I hypothesized that GL2 may regulate seed oil biosynthesis by controlling PHOSPHOLIPASE D ZETA (PLDZ) genes in the embryo. However, my data demonstrated that GL2, and all of the transcription factors known to be required for GL2 expression, influence seed oil accumulation in the embryo by regulating transcription of a seed coat mucilage biosynthetic gene, MUCILAGE MODIFIED 4 (MUM4) in the seed coat. Based on this evidence, I propose that mucilage biosynthesis in the seed coat competes with oil biosynthesis in the embryo for available photosynthate during seed development. This information suggests a promising way to engineer high oil yields in seeds by blocking seed coat mucilage production.
In chapter 3, I characterized deposition of stem cuticular wax, seed coat mucilage and secondary cell wall columella, and secretion in the cer11-1 mutant. The pleiotropic cer11-1 phenotype suggests that CER11 plays a role in secretory trafficking involved in the deposition of apoplastic matrix components, including cuticular wax, seed coat mucilage and cell wall constituents. Cloning of the CER11 gene revealed that it encodes C-TERMINAL DOMAIN PHOSPHATASE LIKE 2 (CPL2) that interacts with a vacuolar type H⁺-ATPase (V-ATPase) subunit C (VHA-C) in yeast and plants. I hypothesize that the role of the CER11/CPL2 in secretory trafficking is to determine phosphorylation levels of VHA-C involved in regulation of V-ATPase activity. === Science, Faculty of === Botany, Department of === Graduate
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