The molecular mechanisms that regulate water-deficit
tolerance are of major economic importance impacting crop production.
Equally important, these mechanisms are fundamental to the processes
that enable plants to survive on dry land. Studies comparing molecular
responses of a plant species to water deficit with control conditions
have netted a catalog of genes that are induced by water deficit.
However, we have not gained an understanding of the responses that
permit tolerance of, or preserve productivity under, water deficits.
Combining a molecular and evolutionary approach, the "Plants
Without Water" Genomics Project will address these questions:
- What are the cellular-level
processes of plant adaptation to water deficits in vegetative
and reproductive structures?
- What homologies can be found
among the genes that control these processes?
- What, if any, is the functional
and evolutionary relationship between water-deficit responses
- To what extent is seed desiccation-tolerance
related to vegetative desiccation-tolerance found in primitive
land plants and in some derived seed plants?
- To the extent that non-tolerant
seed plants retain at least some of the array of genes responsible
for desiccation-tolerance in their ancestors, how might this enhance
the possibility of genetically engineering dehydration-tolerance
"Plants Without Water"
will combine phylogenetic, gene expression and function studies
to generate a molecular picture of mechanisms that control adaptation
to dehydration and the evolutionary link between desiccation tolerance
and water-deficit tolerance in modern crops. We will generate, sequence,
and annotate deep EST samples from a set of ten plants that differ
in tolerance to water deficits, from sensitive to mild stress to
tolerant to desiccation (including selective seed ESTs). Phylogenetic
comparisons of EST data sets will be used to infer evolutionary
relationships and identify potential genes central to the development
of stress tolerance in all species or novel to tolerant species.
Unigene sets for each species will serve as the basis for microarray
expression studies to provide a dynamic picture of each stress response.
Using this information, we will identify a
set of target genes that will be functionally dissected using transgenic
technology in our model crop, tomato. Since the plant hormone ABA
has had a fundamental role in the development of desiccation tolerance,
we will transgenically manipulate ABA biosynthesis and signal-transduction
pathways to evaluate the role of ABA in the adaptation process.
Over-expression and knockout lines will be rigorously tested at
the physiological level for water-deficit tolerance in whole plants
and seeds. This project will generate large EST and expression pattern
data sets across diverse genera for comparative study of dehydration
tolerance in crops. Libraries and microarrays will be archived as
a public resource. Informatics efforts will be co-ordinated with
ongoing plant genome projects providing a large phylogenetic centered
database for comparisons between vegetative and developmental gene
expression. The EST database will provide annotated links to established
genomic and functional information for Arabidopsis, maize, and rice.
"Plants Without Water" will generate new hypotheses
for the functions of genes involved in water-deficit responses and
provide novel strategies for improving water-deficit tolerance in