Crop yield, responses to high CO2 in the atmosphere, and other aspects of plant growth are partially limited and regulated by the transport of nutrients from leaves to distant plants parts, such as roots and grain. The first step in this process, and an important control point, involves loading sugar and other nutrients into the long-distance transport tissue, the phloem. To date, two phloem-loading mechanisms are known, both of which require metabolic energy. In this project the investigators suggest that there is a third mechanism that does not require energy, one that may be used by as many as half of all flowering plants, especially trees. This could explain why some trees are able to use additional atmospheric CO2 without feedback inhibition, which limits growth of herbaceous crop plants under these conditions. The hypothesis will be tested by genetically engineering poplar trees to inhibit active phloem loading. The prediction is that, although such inhibitory treatments severely retard the growth of plants that load actively, they will have little, if any, effect on poplar. Methods of altering transport through the fine pores that connect plant cells, and serve as conducting channels for virus movement, will also be explored. Broader impacts include, 1) testing and potentially restructuring a key tenet of plant nutrient transport, namely that energy is required to load the phloem in preparation for export; 2) determining how some plants use additional CO2 more effectively than others; and 3) potentially developing a transgenic method of restricting virus movement across specific cellular interfaces. Educational broader impacts include training exceptional undergraduates for careers in science, leading a prison education program, teaching a large introductory biology course for non-biology majors, and writing scientific articles for the general public.
