15th International Conference on Arabidopsis Research - TAIR

T12-025
Dissecting symbiotic nitrogen fixation in legumes
Cook, Douglas(1), Ané, Jean-Michel(1), Penmesta, R. Varma(1), Riely, Brendan(1)
1-Department of Plant Pathology, University of California, Davis, CA, USA
Legumes and a few close relatives are unique among plants because they
establish a symbiotic relationship with soil bacteria termed "rhizobia". The
product of this cross-kingdom collaboration is the conversion of atmospheric
di-nitrogen to ammonia. Symbiosis is carried out within a novel plant organ,
the "nodule", where an environment of low oxygen tension and energy from
photosynthate provide conditions for operation of the bacterial nitrogenase
enzyme.
Symbiotic development can be divided into two broad processes: infection
of the plant by the bacterium and development of the nodule organ. Both
infection and development are controlled by the perception of chitin-based
lipooligosaccharide signals (called "Nod factors") of bacterial origin. Remarkably,
components of this signaling pathway are also essential for mycorrhizal
symbiosis in legumes. Pharmacological and cell biological assays implicate
a calcium-sensitive pathway in early Nod factor signaling, while moleculargenetic
characterization reveals a system of receptor-like kinases, a putative
cation channel, and a putative calcium-responsive kinase, each of which are
required for symbiotic development and infection. In all cases, orthologous
proteins are either absent from Arabidopsis or present in Arabidopsis but
not yet characterized. By contrast, other aspects of symbiotic establishment
are derived from pathways where the antecedents are well characterized in
Arabidopsis. Thus, the ortholog of AtEin2 negatively regulates Nod factor
signaling and alters both infection and developmental phenotypes, while a
paralog of clavata 1 regulates the initiation of nodule meristems.
Symbiosis research has been aided by the parallel development of data and
tools related to the structure and function of legume genomes. Medicago
truncatula and Lotus japonicus are the subjects of international genomics
initiatives, with ongoing projects at the whole genome, transcriptome, proteome
and metabolome levels. Hundreds of genes are candidate for nodulation
based on inferences from gene structure and expression studies. Renewed
effort, employing a combination of traditional forward genetics, reverse genetics,
cell biology and biochemistry, will be required to unravel the network of
interacting elements that comprise symbiotic nitrogen fixation.
This presentation will provide an overview of recent progress and current
challenges of nodulation research.
Ané, Science 2004 303:1364
Endre, Nature 2002 417:962
Lévy, Science 2004 303:1361
Limpens, Science 2003 302:630
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T12-026
What plant research will be like 10 years from now.
Steve Briggs(1)
Scientific originality arises from access to technology (the first to be able to
do an experiment) and conception (the first to combine existing ideas in a
particular way). Mainstream plant research has evolved from physiology, “the
effect of this treatment upon that response”, to the integration of physiology
with molecular biology and genetics, “this gene causes that trait”. This trend
of integration will continue to add new technologies from other disciplines
for measuring effects of genes and the environment on plant molecules
and behavior. We will soon be able to identify and quantify all non-polymeric
molecules in a plant sample and this will enable the circuitry of plants to
be described. I will illustrate using our efforts to map genetic networks by
integrating quantitative genetics with genomic mRNA profiling. Application
breakthroughs over the next 10 years will come from emerging concepts at
the interfaces between plant research and the disciplines of microbiology,
ecology, nutrition, and medicine. I will illustrate using microbial genes for
crop processing and improvement. Plant research in 10 years will be led
by scientists with early access to technology and ideas from outside plant
biology focused on solving problems in health and the environment.
T12 Non-Arabidopsis (Limitations of the Arabidopsis Model)