DR. JULIA FRUGOLI
CLEMSON UNIVERSITY

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Gene Nomenclature in
Medicago Truncatula

Medicago.org

Clemson Home Page

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Although nitrogen makes up 70% of the atmosphere, atmospheric nitrogen is unavailable to living organisms until it is reduced ("fixed") by certain prokaryotes. Legumes set up a symbiosis with some of these prokaryotes, supplying carbon for the bacteria while the bacteria fix nitrogen from the air for the plant inside special plant structures called nodules. Since legumes provide 33% of human nutrition in the world, a more detailed understanding of nodule development and the plant control of nodulation would benefit agricultural production. Many of the numerous genes involved plant control of nodulation are probably genes involved in general plant growth and development. My lab applies molecular genetics in the legume model system Medicago truncatula in order to identify genes involved in plant signaling pathways that regulate nodule number and nodule development.

The power of molecular genetics in Medicago truncatula allows us to clone and analyze genes involved in the regulation of nodule number, in order to construct a genetic signal transduction pathway. One nodule number mutant, sunn makes 7-10-fold more nodules than wild type plants. Yet sunn mutants have the same number of infection events, and nodules develop predominantly in the same spatial orientation as in normal plants. Grafting experiments with sunn mutants have shown that the signal regulating nodule number occurs in the shoot [1]. We mapped the SUNN gene [2] and upon cloning it, discovered it encodes a leucine-rich repeat receptor-like kinase, with homology to Arabidopsis CLAVATA1 [3]. Isolation of other supernodulation mutants in collaboration with Sharon Long's lab at Stanford University has allowed us to focus on characterization of other genes that interact with SUNN through biochemical and genetic analysis. These mutants include lss, a shoot controlled supernodulator whose phenotype is essentially identical to sunn, and rdn, a mutant with the same supernodulation phenotype, but root control of the phenotype. We also have a suppressor of the sunn mutation, called rae. We are cloning these genes and have begun to order the genes into a pathway regulating nodule development based on grafting experiments, auxin measurements, expression and epistasis analysis.

One of the components of our model is the plant hormone auxin: we are also interested in the role of auxin in nodulation. The sunn mutant has an increase in auxin flux between the shoot and root, which may account for the supernodulation phenotype [4]. A small project in the lab works with M. truncatula sequence homologs of Arabidopsis auxin efflux carriers (EIR1/PIN homologs) and Arabidopsis auxin permeases (AUX1 homologs) [5] , and auxin reporter genes (DR5::GUS). By disrupting auxin transporters, we have reduced nodule number, suggesting that auxin is part of the nodule regulatory signal [6].

I have a professional interest in research ethics, specifically the encouragement and transmission of ethical research practices (often called "best practices") to graduate students, and the definition of these practices. To that end I interact frequently with Clemson's Rutland Center for Ethics Across the Curriculum.

References:

1. Penmetsa, R.V., J. Frugoli, L. Smith, S.R. Long, and D. Cook, Genetic evidence for dual pathway control of nodule
	number in Medicago truncatula. Plant Physiology, 2003. 131: p. 998-1008.
	
2. Schnabel, E., O. Kulikova, T. Bisseling, V. Penmetsa, D. Cook, and J. Frugoli, An integrated physical, genetic and
	cytogenetic map around the sunn locus of M. truncatula. Genome, 2003. 46: p. 665-72.
	
3. Schnabel, E., E.P. Journet, F. Carvalho-Niebel, G. Duc, and J. Frugoli, The Medicago truncatula SUNN gene encoding
	a CLV1-like leucine-rich repeat receptor kinase regulates both nodule number and root length. Plant Molecular
	Biology, 2005. 58: p. 809-822.
	
4. van Noorden, G.E., J.J. Ross, J.B. Reid, B.J. Rolfe, and U. Mathesius, Defective Long-Distance Auxin Transport
	Regulation in the Medicago truncatula super numeric nodules Mutant. Plant Physiology, 2006. 140: p.1494-1506.
	
5. Schnabel, E. and J. Frugoli, The PIN and LAX families of auxin transport genes in Medicago truncatula. Molecular
	Genetics and Genomics, 2004. 272: p. 420-432.
	
6. Huo, X., E. Schnabel, K. Hughes, and J. Frugoli, RNAi phenotypes and the localization of a protein::GUS fusion imply
	a role for Medicago truncatula PIN genes in nodulation. Journal of Plant Growth Regulation, 2006. 25:p.156-165.

Support:

This research has been supported by the US Department of Agriculture, Clemson University, the National Science Foundation, and awards to undergraduates from Pfizer, the American Society for Plant Biology, and the Howard Hughes Medical Institute (through the SC LIFE program).

Research in My Lab | Selected Publications | My Background
Teaching | Research Ethics | Professional Societies | Lab Members | My Home Page
Gene Nomenclature in Medicago Truncatula | Medicago.org | Clemson Home Page | Department Home Page

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© 2003 Dr. Julia Frugoli