Nodulin-26 Intrinsic Proteins: Multifunctional Transporters of Water and Metabolites in Plant Symbioses and Stress Responses

University Of Tennessee Knoxville, Knoxville TN

Investigators

Abstract

Major Intrinsic Proteins (MIPs) are an ancient family of membrane channels that mediate the selective transport of water and uncharged metabolites. These transporters play a myriad of roles in membrane physiology ranging from renal function and fluid secretion in mammals to osmoregulation, stress adaptation and nutrient uptake and transport in plants and microbes. The MIP family is particularly diverse in plants, reflecting their importance in regulating water relations in plant growth and development and adaptive responses to environmental osmotic challenge. However, recent evidence suggests a broader role for a subclass of plant MIPs known as Nodulin-26 intrinsic proteins or ""NIPs"". These proteins, named for the archetype channel of the family, soybean nodulin 26, have an overall structure similar to other MIPs, but show unique pore structural features that result in multifunctional transport behavior of water as well as critical plant metabolites including ammonia, boron and carbon polyols. The overarching goal of this project is to investigate the structure and function of NIPs as well as mechanisms of regulation and their metabolic roles in planta. The specific goals are three-fold. First, the structure and transport function of two distinct ""pore familes"" of NIPs (NIP I and II proteins) that differ in key pore selectivity regions and show different transport specificity will be investigated. Second, the functional significance of the interaction of soybean nodulin 26 with regulatory proteins (protein kinases and 14-3-3 proteins) and the nitrogen assimilatory enzyme glutamine synthetase, will be investigated. The finding that glutamine synthetase interacts with nodulin 26, which forms an ammonia channel in legume-rhizobia root nodules, is of potential significance to the nitrogen fixation/assimilation process of this plant-microbe symbiosis. Additionally, the ability to bind and recruit cytosolic proteins and metabolic enzymes represents a new emerging interest in MIP research and regulation in general. Third, to examine a new function of NIPs in metabolic adaptation to low oxygen and flooding stress in plant roots using the Arabidopsis protein AtNIP2;1 as a model. The ability of AtNIP2;1 to participate in lactic acid efflux will be investigated as a potential mechanism for pH regulation and prevention of cytosolic acidosis during metabolic adaptation to flooding and low oxygen stress. From the perspective of infrastructure, this project will contribute to the understanding of the molecular basis of nitrogen fixation and assimilation between microbes and plants, as well as stress regulation and metabolic adaptation of plant systems. The work will also contribute to the basic understanding of structure/function relationships of plant MIPs. Broader Impact and Educational Outreach This project will continue to serve in the training of graduate students and postdoctoral fellows in the larger area of Plant Membrane Biochemistry and Physiology, as well as to introduce multiple young undergraduate scholars at the University of Tennessee to modern plant molecular biology and biochemistry research. In addition, this project will also serve as a foundation for the P.I.''s involvement in summer programs and mentoring of Tennessee High School students from diverse backgrounds, including participation in the Governor''s School for Sciences at the University of Tennessee, as well as in minority recruitment activities at the University such as JUMP (Join the University Minority Project). Finally, the project will also support the P.I.''s involvement in a new summer initiative sponsored by the College of Arts and Sciences providing summer educational and laboratory experiences for Tennessee Middle School Teachers.