Integrative approaches for understanding metabolism in plant specialized cell types

Abstract

Plants contain specialized tissues/cell types that play important roles in the synthesis of many natural products. Investigation at cell-specific resolution is necessary for understanding the functional specialization of these specific tissues/cells. In this thesis, I applied integrative approaches to investigate the functions of two cell types: (1) the paraveinal mesophyll (PVM) cells in soybean leaves and (2) the epithelial cells (EC) in grapefruit peel. The PVM layer contains cells with unique ultrastructural properties, and several hypotheses have been developed regarding its functions. We describe a cell type-specific transcriptome effort to evaluate the hypothesized role of PVM cells in accumulating vegetative storage proteins (Vsp) and photoassimilate translocation (Chapter 2). Transcripts related to Vsp and certain vegetative lipoxygenase (Vlx) isoforms were significantly enriched in PVM. Potential roles of Vsp and Vlx in phosphate mobilization and defense responses, respectively, are discussed. Another class of genes enriched in PVM cells was related to the facilitated diffusion of sucrose and various other transporter-related processes. In addition, effects of sink removal experiment (repeated clipping of shoot tips) were investigated in soybean (Chapter 3). At transcriptional level we found an induction of hundreds of transcripts with putative roles in the responses to biotic and abiotic stresses. Our transcriptome data sets also indicated potential changes in amino acid and phenylpropanoid metabolism as a response to sink removal, which was confirmed by metabolic profiling. Taken together, we demonstrate that sink removal leads to an up-regulation of stress responses in distant leaves. Epithelial cells lining the secretory cavities of