Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2007
Publication Date: 4/1/2008
Citation: Allen, M.L., Mertens, J.A. 2008. Molecular cloning and expression of three polygalacturonase cDNAs from the tarnished plant bug, Lygus lineolaris. J. Insect Sci. 8 Article 27:1-14. 2008.
Interpretive Summary: The tarnished plant bug, Lygus lineolaris, damages plants by injecting them with enzymes that dissolve pectin, an important plant structural compound. Before now, the genes for this type of enzyme have been identified only in beetles and fungi. Sequence analysis from an actively feeding stage of this bug identified three unique genes. The genes are active in all developmental stages that feed, from hatching through adult, but not in the eggs. The genes are turned on and off in different combinations throughout the life of the insect, regardless of age or sex. Understanding how these bugs mix enzymes in their saliva to attack plants will help plant breeders develop bug-resistant crops.
Technical Abstract: Three unique cDNAs encoding putative polygalacturonase enzymes were isolated from the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae). The three nucleotide sequences were dissimilar to one another, but the deduced amino acid sequences were similar to each other and to other polygalacturonases from insects, fungi, plants, and bacteria. Four conserved segments characteristic of polygalacturonases were present, but with some notable semiconservative substitutions. Two of four expected disulfide bridge-forming cysteine pairs were present. All three inferred protein translations included predicted signal sequences of 17 to 20 amino acids. Amplification of genomic DNA identified an intron in one of the genes, L1pg1, in the 5' untranslated region. Semiquantitative RT-PCR revealed expression in all stages of the insect except the eggs. Expression in adults, male and female, was highly variable, indicating a family of highly inducible and diverse enzymes adapted to the generalist polyphagous nature of this important pest.