Technical Abstract: Previous research has shown that xylem vessel obstruction (tyloses, plant cell wall component-derived gels and bacterial extracellular polysaccharides) are early consequences of infection with Xylella fastidiosa (Xf), before bacterial populations are substantial and have spread far from the inoculation point. Also, ethylene treatment of vines also triggers vessel obstruction development and reduced water movement. This new project will study the role of GWSS cell wall-degrading salivary enzymes in cell wall breakdown, especially of pit cell membranes. Objectives are to obtain polygalacturonase (PG) and other enzymes from both GWSS and Xf and determine the extent to which PG inhibitor proteins (PGIP) inhibits the PGs from the insect as well as bacteria. Preliminary work to date has shown PG to be present in low but variable amounts in GWSS salivary gland extracts. In contrast, beta-1,4-glucanase (BGase) activity has been substantial in all extracts and is being purified.