Poster: Plant insect-nematode interactions

Abs # 490: Polygalacturonase role in plant damage caused by lygus bug and polygalacturonase inhibiting protein role in plant defense

Presenter:	Celorio-Mancera, Maria de la Paz , mpcelorio@ucdavis.edu
Authors	Celorio-Mancera, Maria de la Paz  (A)   Ahmadi, Hamid  (A)   Greve, L. Carl  (A)   Teuber, Larry R (B)   Shackel, Ken A (A)   Labavitch, John  (A)
Affiliations:	(A): University of California, Pomology Department (B): University of California, Agronomy and Range Science Department

Lygus bug (Heteroptera: Miridae, Lygus bug (Heteroptera: Miridae, Lygus hesperus Knight) feeding causes significant economic losses to many important cultivated plants, including alfalfa and cotton. Plant damage caused by L. hesperus was suggested to be principally due to the activity of the insect’s polygalacturonase (PG) secreted during feeding. Fungal PG has been considered important in the development of plant diseases, degrading the pectin component of the cell wall. A plant’s pathogen defenses may include a role for the interaction of the plant’s polygalacturonase inhibiting proteins (PGIPs) with pathogen PGs. We have found PGIP activity in extracts of cotton and alfalfa. Therefore, our study examines how lygus PG contributes to the cosmopolitan feeding habit of the insect and whether PGIPs contribute to the plant’s defenses against the pest. We have identified PG and other digestive enzymes (amylase, protease and endo-1,4-β-glucanase) in extracts of lygus heads, salivary glands and plant tissue and diet solutions that the insects have fed upon. A partially purified PG has been isolated from a lygus head extract and injected into alfalfa and cotton flower buds using a micro pressure probe, which mimics the insect stylet; this treatment caused tissue damage resembling that originated by lygus bug feeding. Cotton and alfalfa tissue extracts contain PGIP that inhibits lygus PG and the germplasm of these crops has been screened to identify lines with high PGIP content. Transgenic lines with expression of pear fruit PGIP are also being screened. These materials will be tested for damage level following PG injection or lygus exposure to test whether PGIP ameliorates feeding damage. Future work will describe the interaction of purified lygus PG with PGIPs in vitro.