ARS | Publication request: Lygus hesperus polygalacturonase Characterization and Role in Plant Damage

Submitted to: Journal of Insect Science
Publication Type: Proceedings
Publication Acceptance Date: June 14, 2007
Publication Date: September 17, 2008
Citation: Celorio-Mancera, M., Greve, C.L., Ahmadi, H., Teuber, L., Shackel, K.A., Allen, M.L., Labavitch, J.M. Lygus hesperus polygalacturonase Characterization and Role in Plant Damage. In P. B. Goodell and P.C. Ellsworth, Second International Lygus Symposium Asilomar. J. Insect Sci. 8 article 49:7. 2008.

Technical Abstract: The amino terminus, of a Lygus hesperus salivary gland protein revealing polygalacturonase (PG) activity in an SDS-PAGE activity gel assay, has been sequenced via Edman degradation. The N-terminal amino acid sequence shares homology with the predicted amino acid sequence for putative L. lineolaris PGs identified in an EST database. The molecular weight of the L. hesperus PG is about 35.5 KDa, similar to molecular weights predicted for the L. lineolaris PG sequences in the database. In addition, the in silico digestion of the putative L. lineolaris PGs yielded peptide sequences similar to those identified by liquid chromatography-mass spectrometry-mass spectrometry peptide fingerprinting of the L. hesperus PG. L. hesperus peptides represent 51% coverage of peptides predicted for L. lineolaris PG 1, 48% coverage of L. lineolaris PG 2, and 26% of L. lineolaris PG 3. Insects of the species L. hesperus, reared on artificial diet, were moved to a “collection diet” for recovery of saliva. Extracts of the fed-on collection diet showed PG activity in a semi-quantitative enzyme activity assay while the control (not fed-on collection diet) yielded no activity. Proteins from the fed-on and control collection diets were subjected to peptide fingerprinting and compared with the peptides predicted by the putative L. lineolaris PG sequences. PG peptides shared by L. hesperus and L. lineolaris were detected in the protein sample from fed-on collection diet. Our previous research has indicated that the micro-injection of a partially purified PG protein, from a crude L. hesperus head-pronotum protein extract, into developing alfalfa florets, resulted in plant injuries similar to those caused by Lygus feeding. Moreover, while microinjection of an enzymatically active Aspergillus niger PG II recombinant protein produced damage symptoms (67% of the florets injected stopped in their development, were discolored, and/or abscised), the microinjection of an inactive, mutant A. niger PGII caused no damage (0% of the florets injected were symptomatic). This demonstrated that PG activity was required to cause floret damage.