| Original Project Abstract
Genes encoding NBS-LRR containing proteins
are one of the most prevalent classes in plant genomes, with
~165 of these genes in the recently completed Arabidopsis
genome, and probably many more in rice. However, little is known
of their function. Sequence motifs indicate that they act at
the beginning of signaling pathways. The only demonstrated function
for these genes is in disease or pest resistance, but they may
also be involved in other aspects of plant biology including
development and response to the environment.
The objectives of this project are to complete
a detailed functional analysis of NBS-LRR genes in Arabidopsis
and a comparative analysis of representatives in maize and rice.
Broad functional classes of NBS-LRR encoding genes will be established
and the specific functions of a subset of these classes will
be characterized. Genes induced by the action of NBS-LRR gene
products will be identified. NBS-LRR encoding genes identified
in the Arabidopsis genome sequencing project will be characterized
in a high-throughput format using ligand-independent approaches
involving either over-expression or gain-of-phenotype variants.
Microarrays will be used to determine changes in global expression
patterns caused by expression of NBS-LRR genes and will also
look for gross developmental and physiological changes. The expression
array data will provide an 'induced expression signature' for
each gene that will indicate its function as well as allow them
to be assigned into functional classes. The expression signature
of known resistance genes, such as RPS4, RPS2, RPM1
and RPP8, will be characterized and compared to the expression
signatures of the unknown genes.
Homologs representing each functional class
identified in Arabidopsis will be studied in an analogous
fashion in rice and maize. Homologs will be obtained from databases
or amplified de novo using conserved oligonucleotide primers.
Using parallel approaches to those employed for Arabidopsis,
induced expression signatures for each homolog will be determined
using diagnostic microarrays for rice and maize. These diagnostic
arrays will be developed by selecting clones of cereal sequences
available in the database using expression data from Arabidopsis
plus other putative defense genes from each of these species.
Each NBS-LRR homolog will be mapped onto the consensus genetic
map for each species relative to a variety of phenotypes.
This global approach will efficiently provide
functional information on approximately 165 genes in the model
plant, Arabidopsis, and will extend this information to
two important crop species. The work will define the different
classes of resistance genes and identify those with other functions;
this will establish how many act as resistance genes and how
many control processes unrelated to defense. It will also identify
sets of downstream genes regulated by each class. This will provide
the basis for detailed studies into the action of specific NBS-LRR
and downstream genes. It will provide tools to facilitate the
practical manipulation of plant disease resistance and may ultimately
provide the ability to manipulate diverse aspects of plant development
This project is funded under the National
Science Foundation, Program #1329, Award # 9975971.