Heterogeneity in the phloem of minor veins

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The phloem transports nutrients, developmental signals and defense compounds throughout the plant body. It is often assumed that the phloem is a homogeneous tissue. However, on the basis of preliminary data the investigators suggest that, in the small veins of leaves where transported materials are loaded into the phloem, the network is heterogeneous in its structure and biochemistry, with specific functions assigned to distinct subsets of phloem cells. This hypothesis will be tested in several species by a number of techniques. Both light and electron microscopy will be used to quantify cell-specific features involved in transport, including the channels (plasmodesmata) that connect the phloem to surrounding cells. Cell-specific promoters (the DNA elements that control gene expression) will be used to identify cell types within veins and this information will be used in conjunction with microscopy to profile gene expression patterns in the different cell types. In a third project, specific phloem cells will be selectively killed with a toxin synthesized under the control of cell-specific promoters and these plants will be used to obtain and characterize phloem sap to identify nutrients, macromolecules and defense compounds transported in individual cell types. In terms of broader impacts, specific cells involved in the synthesis and transport of compounds required for the proper development and health of crop plants will be identified. Educational broader impacts include the incorporation of experimental hypotheses and results in undergraduate course material, employment of undergraduate students in phloem sap studies, and continued participation in the Cornell Prison Education Program. RNA sequence data will be deposited at the National Center for Biotechnology Information and processed data files will be uploaded to iPlant.