Martin H. Spalding

Ph.D., University of Wisconsin, 1979

Mail:

• Dept. of Botany
• 353 Bessey Hall
• Iowa State University
• Ames, IA 50011-1020

Research Interests

Research in the Spalding lab focuses on the regulation of carbon metabolism and carbon partitioning in plants and other photosynthetic organisms. A primary interest is how photosynthetic cells monitor their carbon status and regulate genes involved in carbon assimilation in response to carbon availability. This is an example of metabolic regulation of gene expression, where products of metabolism act as signals in the regulation of gene expression. The lab is involved with projects in this area using Chlamydomonas, Synechocystis and higher plants.

Acclimation of the unicellular green alga Chlamydomonas and the cyanobacterium Synechocystis to changes in CO2 is being used as model systems for exploring metabolic regulation of gene expression in a photosynthetic eukaryote and a photosynthetic prokaryote, respectively. Each of these photosynthetic organisms exhibits a syndrome of adaptive responses to limiting CO2, including induction of an active CO2-concentrating mechanism (CCM). In Chlamydomonas we are dissecting both the signal transduction pathway for adaptation to changes in CO2 and the microalgal CCM using insertional mutagenesis to generate tagged mutants, which are being used to clone the key genes in the pathway. Identification of a key gene in the Chlamydomonas signal transduction pathway, Cia5, has provided the opportunity to identify genes/proteins that interact with it using both suppressor analysis and the yeast two-hybrid system. In Synechocystis, for which we have a completely sequenced genome available, several mutants deficient in acclimation to limiting CO2 concentrations have been identified by transposon mutagenesis and the defective genes identified. Interacting components are being identified using suppressor analysis.

In photosynthetic eukaryotes, the best characterized example of metabolic regulation of gene expression is the regulation of photosynthesis-related genes by carbohydrates. In collaboration with Steven Rodermel, metabolic regulation of gene expression in higher plants by sugars is being investigated using transgenic tobacco and Arabidopsis. This project includes investigation of carbohydrate accumulation as a signal regulating expression of photosynthesis-related genes and regulating the onset of leaf senescence.

In collaboration with Dr. Jaylin Jane (Food Science & Human Nutrition) we are trying to understand the mechanism of starch granule development using the cyanobacterium Synechocystis as a simple model system to investigate factors necessary for the formation of starch granules. Our hypothesis is that the branching structure of starch, along with an environment rich in lipids, are requisites for starch granule development, suggesting that it should be possible to generate granular starch in a cyanobacterium, which normally makes glycogen (a soluble glucan) rather than starch, by duplicating the branching characteristics of starch within intermembrane regions where glycogen normally is synthesized.

Another new research area involves two major collaborative projects investigating the factors controlling partitioning of carbon metabolites in developing soybean embryos. These projects utilize isogenic soybean lines that differ markedly in their oil and protein contents, and represent part of a larger, campus-wide effort to investigate the factors controlling carbon and nitrogen partitioning into oil versus protein in these isogenic lines. Involvement of the Spalding lab includes analysis, in collaboration with Mark Westgate (Agronomy), of changes in the proteome early in the development of soybean embryos in the isogenic lines, and application, in collaboration with Jackie Shanks (Chemical Engineering) and Mark Westgate, of a novel metabolic flux mapping technique, Metabolic Flux Ratio Analysis (METAFoR), to provide information about how the carbon flux through key steps in intermediary metabolism changes in developing soybean embryos across time, space or genotype. Metabolic Flux Ratio Analysis (METAFoR) combines NMR analysis of fractional 13C labeling of proteinogenic amino acids and metabolite balance models to estimate fluxes through the pathways of intermediary metabolism.

The Spalding lab also is working on another, somewhat unrelated project involving development of a mechanism for coordinated expression of multiple secreted proteins in transgenic plants. Preliminary results have shown promise that this mechanism may prove useful in the plant biotechnology industry.

Recent Publications

• Dillard, S, K Van, MH Spalding (in preparation) Response of the Chlamydomonas reinhardtii cell division cycle to changes in carbon availability.
• Nakamura, Y, S Kanakagiri, K Van, MH Spalding (in preparation) Disruption of a glycolate dehydrogenase gene in a high-CO2-requiring mutant of Chlamydomonas reinhardtii.
• Yoo, S-H, L Li, SDN. Pieris, Y Moon, MH Spalding, J Jane (in preparation) Insertional Mutagenesis of Glycogen Synthase Genes in Cyanobacterium Synechocystis sp. PCC6803.
• Yoo, S-H, C Keppel, MH Spalding, J Jane (in preparation) Effects of growth conditions on the yield and structure of glycogen in the cyanobacterium Synechocystis sp. PCC6803.
• Yoo, S-H, MH Spalding, J Jane 2002 Characterization of cyanobacterial glycogen isolated from the wild type and from a mutant lacking of branching enzyme. Carbohydrate Research 337:2195-2203.
• Spalding, MH, K Van, Y Wang, Y Nakamura 2002 Acclimation of Chlamydomonas to changing carbon availability. Functional Plant Biology 29:221-230.
• Stessman, D, A Miller, MH Spalding, S Rodermel 2002 Regulation of photosynthesis during Arabidopsis leaf development in continuous light. Photosynthesis Research 72:27-37.
• Van, K, Y Wang, Y Nakamura, MH Spalding 2001 Insertional mutants of Chlamydomonas reinhardtii that require elevated CO2 for survival. Plant Physiology 127: 607-614.
• Rodermel, S, A Miller, M Spalding 2001 Influence of source strength on leaf developmental programming. In (M Pessarakli, ed) Handbook of Plant and Crop Physiology. Marcel Dekker, Inc., New York, NY, USA, pp. 117-126.
• Badger, MR, MH Spalding 2000 CO2 acquisition, concentration and fixation in cyanobacteria and algae. In (RC Leegood, TD Sharkey, S von Caemmerer, eds) Photosynthesis: Physiology and Metabolism. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 369-397.
• Miller, A, C Schlagnhaufer, MH Spalding, S Rodermel 2000 Carbohydrate regulation of leaf development: prolongation of leaf senescence in Rubisco antisense mutants of tobacco. Photosynthesis Research 63:1-8.
• Nichols, DJ, PL Keeling, MH Spalding, H Guan 2000 Involvement of conserved aspartate and glutamate residues in the catalysis and substrate binding of maize starch synthase IIb-2. Biochemistry 39:7820-7825.
• Van, K, MH Spalding 1999 Periplasmic carbonic anhydrase (Cah1) structural gene mutant in Chlamydomonas reinhardtii. Plant Physiology 120:757-764.
• Miller, AM, MH Spalding, S Rodermel 1999 Leaf development and acclimation to elevated CO2. In (M Pessarakli, ed.) Handbook of Plant and Crop Stress. Marcel Dekker, New York. Pp. 1129-1135.
• Kimber, A, WG Crumpton, T Parkins, MH Spalding 1999 Sediment is a carbon source for the submersed macrophyte Vallisneria. Plant Cell and Environment 22:1595-1600.
• Spalding, MH 1998 CO2 acquisition: Acclimation to changing carbon availability. In J-D Rochaix, M Goldschmidt-Clermont, S Merchant, eds., The Molecular Biology of Chloroplasts and Mitochondria in Chlamydomonas. Kluwer Academic Publishers, Dordrecht, The Netherlands. Pp. 529-547.
• Miller, A, C-H Tsai, D Hemphill, M Endres, S Rodermel, MH Spalding 1997 Elevated CO2 effects during tobacco leaf ontogeny: A new perspective on acclimation. Plant Physiology 115:1195-1200.
• Tsai, C-H, A Miller, MH Spalding, S Rodermel 1997 Source strength regulates the transition to the adult phase of tobacco shoot development. Plant Physiology 115:907-914.

updated January 2003

I.S.U. Botany   Faculty  Graduate Programs   Class links