ARS | Publication request: EXAMINING THE POTENTIAL UTILITY OF POLYGALACTURONASE-POLYGALALACTURONASE INHIBITING PROTEIN INTERACTIONS FOR PROTECTING CROP PLANTS AGAINST LYGUS BUG

Submitted to: American Society of Plant Biologists Annual Meeting - Western Section
Publication Type: Abstract Only
Publication Acceptance Date: January 22, 2007
Publication Date: February 3, 2007
Citation: Celorio-Mancera, M., Greve, L., Allen, M.L., Teuber, L.R., Labavitch, J.M. 2007. Examining the potential utility of polygalacturonase-polygalalacturonase inhibiting protein interactions for protecting crop plants against lygus bug. http://www.ias.unu.edu/Proceedings/ICIBS/IC-MFA/.

Technical Abstract: Lygus bug (Lygus hesperus) feeding causes significant economic losses to many important cultivated plants, including alfalfa and cotton. Strong (1970) suggested that crop damage caused by L. hesperus was principally due to the activity of the insect’s polygalacturonase (PG) secreted during feeding. PG is an enzyme that catalyzes the hydrolytic cleavage of simple cell wall pectin polymers. PG is produced by plants, fungi, bacteria, and several insects and nematodes. Fungal PG has been considered an important virulence factor in the development of plant diseases, degrading the pectin component of the cell wall and facilitating pathogen ingress and colonization of host tissues. A plant’s pathogen defenses include a role for the interaction of the plant’s PG- inhibiting proteins (PGIPs) with pathogen PGs. We have identified PG and other digestive enzymes (amylase, protease and endo-1,4-beta-glucanase) in extracts of Lygus heads, salivary glands and plant tissue and diet solutions that the insects have fed upon. Furthermore, we have found PGIP that inhibits Lygus PG in cotton and alfalfa protein extracts. 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. Therefore, our immediate goal is the purification of the interacting proteins. Protein separation techniques yielded the partial purification of a number of Lygus PG isozymes based on their biochemical characteristics such as glycosylation and charge. The PG isozymes were isolated from salivary glands of wild insects collected at alfalfa field sites. Products of the enzymatic reaction catalyzed by the different isozymes isolated were analyzed by high performance liquid chromatography (HPLC). Although further biochemical characterization of the isolated PGs is needed, the HPLC data suggest the presence of at least one endo-acting PG and one exo-PG. The amino terminus of a protein showing PG activity based on a SDS-PAGE activity gel has been sequenced. The amino acid sequence shares almost complete homology with the putative PG amino acid sequence generated from a Lygus lineolaris EST database. In addition, five PG isoforms produced by the fungus Botrytis cinerea were tested against cotton PGIP. This test was conducted aiming to use these recombinant fungal PGs for affinity chromatographic purification of the cotton PGIP. Three out of the five isoforms were inhibited by the cotton protein leaf extract. Cotton germplasm generated by three years of conventional breeding effort to increase the content of endogenous PGIP is being used as source for cotton PGIP isolation.