There is a wealth of evidence that the metabolic cost of defense is large in comparison to resources available for growth in plants. The abundant phenolic glycosides (PG) of Populus tree species are derived from salicylic acid, a metabolite that is central to the defense of herbaceous and woody plant species, but whose accumulation is extremely costly to herbaceous plant growth. By investigating the functional genomics of PG regulation in a range of hybrid and transgenic Populus, we expect to learn how these plants accommodate such costly outlays, and to identify genes of potential agricultural importance. Cottonwood hybrids varying widely in leaf PG content and growth will be used to obtain differentially expressed PG-regulating and PG-sensitive genes. PG inductive treatments including nitrogen limitation and methyl-jasmonate application will be used to perturb PG homeostasis in the hybrids as well as in transgenically modified aspen, and to verify gene function and assess PG-growth interactions. EST sequences and microarray gene expression profiles derived from this work will be deposited in GenBank and accessible at www.aspenDB.mtu.edu. cDNA microarrays will also be made available to the research community. Information about the release schedule and fee structure of ESTs, arrays, and other biological resources will be posted on the project website at aspenDB.mtu.edu. Project findings will bear particular relevance to the NPGI goal of understanding efficiency of photosynthate utilization in a renewable resource.
There are several anticipated broader impacts. A deeper understanding of the molecular basis of tree carbon budgeting should be of value to ongoing investigation of Populus as keystone ecological species whose productivity and phytochemisty is particularly sensitive to global changes in atmospheric pollutants and greenhouse gases. There are also agricultural crop implications due to possible interplay between PG and condensed tannin (CT) regulation, and the effects of CT on forage digestibility/quality. The value of Populus as a model organism for linking functional genomics to ecological research will be disseminated via a professional microarray workshop targeting tree physiologists and ecophysiologists in year 4. Because aspen is important to the regional economy its use in the planned K-12 educational activities is particularly relevant. Planned outreach activities will emphasize the significance and value of basic research to participating students and their families.
