"FUEL-PATH aims at providing new knowledge on plant cell wall and innovative biotechnological solutions for biomass utilization. A key process for biomass utilization is the initial degradation of cell walls into fermentable sugars (saccharification); this is hindered by the wall recalcitrance to hydrolysis. We propose to improve the plant saccharification characteristics by mimicking a strategy successfully used by phytopathogenic microorganisms. These produce pectic enzymes before other cell wall-degrading enzymes (CWDEs) to weaken the linkages between the wall components and favour the maceration of the plant tissue. Homogalacturonan (HGA), a major component of pectin, is synthesized in a methylated form and is de-esterified in the wall by methylesterases (PMEs). De-esterified HGA interacts with calcium to form ""egg-box"" structures, which are critical for maintaining the integrity of the entire wall. We propose to improve saccharification by expression in plants of microbial polygalacturonases (PGs) hydrolizing HGA. Plants expressing a fungal PG have reduced levels of HGA and enhanced saccharification (unpublished preliminary data). Since PG activity in pianta affects normal growth, a technology of enzyme control through the use of specific protein inhibitors will be developed. A second strategy to be adopted for weakening the ""egg-box"" is the overexpression of PME inhibitors. This may cause not only an increased degradability but also an enhanced biomass production. FUEL-PATH will provide detailed information on the structure, function and construction of tailor-made enzymes and inhibitors suitable for the saccharification process. FUEL-PATH will also address the relationship between pectin composition and developmental responses mediated by hormones in PG-expressing plants. A genetic screen will be performed to isolate genes involved growth defects and increased cell wall degradability and these will be characterized for a possible biotechnological use."