Integrated Studies on the Phloem as a Long-Distance Communication System in Plants

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Biological systems utilize sophisticated control networks to orchestrate complex processes underlying their cellular, developmental and physiological programs. In the plant kingdom, unique systems evolved for inter-organ communication. Signaling around the body of the plant occurs by delivery of information molecules via the xylem tracheary cells, which are dead at maturity, and the phloem sieve tube system. The evolution of this vascular network reflects, among other things, the need to communicate environmental inputs (abiotic and biotic), sensed by mature organs, to meristematic regions of the plant. An important consequence of this long-distance signaling system is that newly forming organs can develop properties optimized for the environment into which they will emerge, mature and function. This proposal describes experiments aimed at further characterizing the role of the phloem in long-distance signaling. To this end, pumpkin will be used as a model plant to collect phloem sap that will be analyzed by mass spectrometry and bioinformatics methods to identify the population of proteins that are present in the higher plant translocation stream. Analysis of the phloem proteome, comprising the proteins present in the translocation stream, will yield novel insights into the spectrum of metabolic and signaling pathways that operate within the unique enucleate sieve tube system of the angiosperms. Long term goals are to identify the pathways that (a) maintain the enucleate sieve tube system and (b) integrate developmental and physiological processes between distantly located organs of the plant. The results from these studies should provide new perspectives on the path taken by the plant kingdom during its evolution from single cells to complex, supracellular, organisms. Finally, the long-term impact of this phloem proteome will be through the development of new controls over plant processes, including the way nutrients are shared between the various plant organs. Such applications could well have major ramifications in terms of agriculture and animal/human nutrition/health.