Differentially Expressed Genes Associated with Post-Harvest Processing in Lolium temulentum L.

Authors: Baldwin, James; Dombrowski, James; Martin, Ruth; Banowetz, Gary

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2007
Publication Date: 4/8/2007
Citation: Baldwin, J.C., Dombrowski, J.E., Martin, R.C., Banowetz, G.M. 2007. Differentially Expressed Genes Associated with Post-Harvest Processing in Lolium temulentum L. Plant Science.173:73-83.

Interpretive Summary: Forage and turf grasses provide the basis for pasture-based livestock production, as well as residential, commercial and recreational turf. In many locations their presence provides high quality buffering to enhance water quality and prevent erosion. Some traits of these grasses that are desirable in seed-producing areas, are undesirable in end-use areas. For instance, after grasses initiate the sequence of events that will lead to seed production, forage quality diminishes. If the final use for the grass is bioenergy feedstock rather than forage, the changes associated with seed production make it more difficult to extract sugars for liquid fuel production. We reasoned that given sufficient information about genes that are turned on after these grasses are cut, it should be able to utilize genetic approaches that would initiate physiological changes within the cut grass that improves its chemical composition for forage or biofuel production. The first in this approach is learning which genes are turned on after grass is cut. Accordingly, we utilized the model grass Lolium temulentum, a ryegrass to characterize post-harvest gene expression. We found 598 unique gene sequences whose apparent expression was enhanced after harvest. Many of these sequences corresponded to previously identified genes.We evaluated whether the expression of these genes was restricted to post-harvest and found that the expression of at least two of these genes increases dramatically after harvest. This first step enables us to proceed with development of a genetic approach to improve the quality of the cut grass as forage and biofuel feedstock.

Technical Abstract: Forage and turf grasses provide the basis for pasture-based livestock production, as well as residential, commercial and recreational turf. In many locations their presence provides high quality buffering to enhance water quality and prevent erosion. Optimal production of seed that enables establishment of forage and turf areas involves harvest of grass plants while they are still green and physiologically active. The cut grass is allowed to cure in the fields for 1-2 weeks prior to harvesting the seed. After seed harvest, a large portion of the generated biomass is left as unused or low value straw. In many of the seed-producing areas of the U.S., there is little market for this biomass as animal feed and biochemical composition of this lignocellullsic feedstock limits its utility in biofuel conversion efforts. One potential approach to improve the utility of grass residues as feed or biofuels is the modification of biochemical or molecular processes within the plant during the period after swathing and seed harvesting. Unfortunately, little knowledge exists regarding post-harvest gene expression that occurs after these grasses are cut. To this end, we utilized the model grass Lolium temulentum, a diploid self-fertile species with a short life cycle (2-3 months), to characterize post-harvest gene expression. This approach represented the first step in identifying promoters with potential utility as regulators of post harvest gene expression. A PCR based subtractive suppression hybridization library of a simulated grass straw harvest was prepared and 598 unique sequences whose apparent expression was enhanced after harvest were identified. Many of these sequences corresponded to orthologs of previously identified genes. The expression patterns of seven genes were evaluated by Northern blot analysis in post-harvest leaf and stem tissues. Expression of a dehydrin sequence and a senescence-related protein showed apparent increases through 48 h post-harvest. These preliminary studies support the concept of utilizing L. temulentum as a model forage grass for molecular genetic analyses of post harvest gene expression.