Molecular Investigation into the Role Played by Tobacco and Arabidopsis NCAPP1 Genes in Plasmodesmal Function

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During the process of evolution, biological systems developed ever-increasingly sophisticated control systems to regulate the complex processes underlying cellular, developmental and physiological programs. The functioning of complex animal and plant tissues and organs required the development of a network of signaling pathways. Present day signaling systems can be divided into two categories. The first involves signaling molecules that act within the cell in which they are expressed; i.e., these molecules are said to be cell-autonomous in behavior. The second group involves signals that act beyond their sites of production; i.e., these signaling molecules act in a non-cell-autonomous manner and can involve hormones, chemical compounds, proteins and RNA molecules. Such signals can move to neighboring cells by secretion, followed by diffusion through the extra-cellular space; this pathway is common to all organisms. Alternatively, in the plant kingdom, these signals can move between cells through specialized structures termed plasmodesmata. The architecture of the plasmodesmata creates cytoplasmic channels through which these signals can move without exiting the cell. Here, it is important to note that the structure of plasmodesmata allows for the movement of proteins and RNA molecules. Signaling around the body of the organism occurs by passage through the plant vascular system. Here again, the movement of proteins and RNA is facilitated by the special properties of the plasmodesmata. The importance of these signaling pathways and signaling molecules is well-supported by published works; however, few studies have provided explicit information on the nature of the essential components. In addition, little is known about the manner in which trafficking of non-cell-autonomous signals is regulated.Solutions to these open questions are now possible through work that developed biochemical methods for the identification of plasmodesmata proteins that regulate the cell-to-cell trafficking of non-cell-autonomously functioning signaling molecules. The first gene identified using this approach was NON-CELL-AUTONOMOUS PATHWAY PROTEIN-1 (NCAPP-1). The present proposal describes experiments aimed at further characterizing the NCAPP-1 gene family. This work will involve three objectives: (a) establishing the role played by the NCAPP-1 gene family in the cell-to-cell signaling pathway; (b) isolating and characterizing proteins that interact with NCAPP1; and (c) employing an inactive form of NCAPP-1 to test whether transport of proteins through plasmodesmata plays a role in the integration of physiological and developmental processes at the whole-plant level. These studies should provide important insights into the way these proteins can influence protein delivery to neighboring cells. This knowledge would allow scientists to more fully understand the signaling networks operating at the cellular, tissue and whole-plant levels. Such progress would have direct bearing on the areas of integrative and developmental plant biology, by establishing an experimental basis for future studies on whole-plant signaling. Finally, these studies should provide new perspectives on the path taken by the plant kingdom during its evolution from single cells to complex, supracellular, organisms. Broader Impacts: This research project would be used to train junior scientists within the area of integrative plant biology. The importance of these scientists to our society would be two-fold. First they would serve as trained teachers who can educate society in the areas of the biological sciences and biotechnology. Secondly, and of equal importance, these scientists could apply this knowledge to 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.