Dan Roberts, Ph. D.
Department of Biochemistry and Cellular
and Molecular Biology
Phone: (865) 974-4070
Office: 133 Hesler Biology
The Major Intrinsic Protein (MIP) family represents an ancient family of membrane channels that mediate the selective transport of water and uncharged solutes. The aquaporins represent the most well-characterized transporters in this family, and these proteins play myriad physiological roles by the bulk movement of water driven by osmotic and pressure gradients. Compared to other kingdoms, plants have evolved a greater number of MIP channels, and recent evidence suggests this has been accompanied with a greater diversity of transport selectivity and biological functions that transcend the traditional “aquaporin” designation. One such subfamily of plant specific MIP channels, the Nodulin-like Instrinsic Proteins (NIPs) which are a diverse family of transporters found in all land plants. A major focus of our laboratory is the analysis of the structure, function and regulation of NIP transport channels, and the evaluation of their multiple biological roles in metabolism, symbiosis and stress physiology. Specific project areas include:
- Role of the nodulin protein Nod26 in metabolism and osmoregulation in nitrogen fixing root nodules The archetype of the family is nodulin 26 which was originally discovered as a major component of the symbiosome, an organelle that is formed during the nodulation of legume roots with soil bacteria of the Rhizobaceae family. Recent evidence suggests that nod26 is involved in a dual transport role, serving as: 1. an aquaporin involved in osmoregulation and gas diffusion during nodule responses to environmental stress and 2. An ammonia gas transporter that physically acts with nitrogen assimilatory enzymes aiding in rapid assimilation of fixed ammonia. The role of each of these activities in nodule physiology and their regulation by posttranslational phosphorylation is being pursued by biochemical, cell biological and molecular genetic approaches.
- Evaluation of the roles of Arabidopsis NIPs in metalloid nutrition and adaptation to hypoxia stress All plant species, even nonlegumes, have multiple NIP genes. Even though NIPs have the same conserved structural fold (the “hourglass fold”) as the aquaporins, they have diversified and evolved into two broad pore families (NIP I and NIP II) that have distinct biological functions. As a result, NIPs are multifunctional channels that mediate the transport of a wide variety of biological substrates including metalloid nutrients and metabolites (e.g., boric and silicic acid), ammonia, glycerol and lactic acid. Research in this area is focused on using a two prong approach. First, biochemical and biophysical analyses are used to investigate transport pore structure, and transport selectivity and regulation. Second, molecular biological and genetic tools are used to investigate the biological functions of these transporters in nutrition and metabolic stress responses.
P. Masalkar, I.S. Wallace, J.H. Hwang, and D.M. Roberts (2010) Interaction of cytosolic glutamine synthetase with the nodulin 26 channel on the soybean symbiosome membrane. J. Biol. Chem. 285, 23880-23888. (selected for as a featured “paper of the week”) [Article]
J.H. Hwang, S.R. Ellingson, and D.M. Roberts (2010) Ammonia permeability of the soybean nodulin 26 channel. FEBS Lett. 484, 4339-4343. [Article]
D.M. Roberts, J.H. Hwang, and W.G. Choi (2010) Strategies for Adaptation to Waterlogging and Hypoxia in Nitrogen Fixing Nodules of Legumes. in Waterlogging Signalling and Tolerance in Plants. (S. Mancuso and S. Shabala, eds.). Springer-Verlag Berlin Heidelberg, pp. 37-59.
A.J. Shakesby, I.S. Wallace, H.V. Issacs, J. Pritchard, D.M. Roberts, and A.E. Douglas (2009) A Water-Specific Aquaporin Involved in Aphid Osmoregulation. Insect Biochemistry and Molecular Biology 39, 1-10. [Article]
M. Tanaka, I.S. Wallace, J. Takano, D.M. Roberts, and T. Fugiwara (2008) NIP6;1 Is a Boric Acid Channel for Preferential Transport of Boron to Growing Shoot Tissues in Arabidopsis thaliana. Plant Cell, 20, 2860-2875. [Article]
W.G. Choi and D.M. Roberts (2007) Arabidopsis NIP2;1: a major intrinsic protein transporter of lactic acid induced by anoxic stress. J. Biol. Chem. 282, 24209-24218. [Article]
I.S. Wallace, W.G. Choi, and D.M. Roberts (2006) The Structure, Function and Regulation of the Nodulin 26-like Intrinsic Protein Family of Plant Aquaglyceroporins, Biochim. Biophy. Acta Biomembranes, 1758, 1165-75. [Article]
J.F. Guenther, S. Seki, F.W. Kleinhans, K. Edashige, D.M. Roberts and P. Mazur (2006) Extra- and intracellular ice formation in stage I and II Xenopus laevis oocytes. Cryobiology 52, 401-16. [Article]
E.D. Vincill, K. Szczyglowski, and D.M. Roberts (2005) GmN70 and LjN70: Anion transporters of the symbiosome membrane of nodules with a transport preference for nitrate. Plant Physiol. 137, 1435-44. [Article]
I.S. Wallace and D.M. Roberts (2005) Distinct transport selectivity of two structural subclasses of the Nodulin-like Intrinsic Protein family of plant aquaglyceroporin channels. Biochemistry 44, 16826-34. [Article]