Identification of genes potentially responsible for extra-oral digestion and overcoming plant defense from salivary glands of the tarnished plant bug (Lygus lineolaris) using cDNA sequencing

Authors: Zhu, Yu Cheng; Yao, Jianxiu; Luttrell, Randall

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2016
Publication Date: 6/20/2016
Citation: Zhu, Y., Yao, J., Luttrell, R.G. 2016. Identification of genes potentially responsible for extra-oral digestion and overcoming plant defense from salivary glands of the tarnished plant bug (Lygus lineolaris) using cDNA sequencing. Journal of Insect Science. 16(1):60;1-11.

Interpretive Summary: The tarnished plant bug has become the most destructive insect on southern row crops, especially on cotton. Currently, management of this serious pest relies almost exclusively on chemical insecticides. Considering the adverse impact of pesticides on environment and non-target organisms, alternative control strategies against TPB are urgently needed. Biotechnologies, such as RNAi, have already showed some successes in insect pest management (Price and Gatehouse 2008; Pitino et al. 2011; Abdellatef et al. 2015). In an attempt to characterize TPB feeding damage and the interaction with host plants, we demonstrated that cotton bolls were seriously stunned and lint was tainted by TPB feeding. The damage might be caused by digestive enzymes and other adverse effectors from salivary gland secretion by TPBs. This study aimed at identification of gene profiles and revealing of damaging enzymes/effectors in the saliva of TPB. More than 60 enzymes were identified in this study, including several detoxification (overcome host plant defense)-, cell wall degradation-, and extra-oral (proteins, lipids, and carbohydrates) digestion-related enzymes. The data from this study provided useful information necessary for future development of novel techniques (such as novel enzyme inhibitors and RNAi) to control TPBs.

Technical Abstract: Saliva is known to play a crucial role in tarnished plant bug (TPB, Lygus lineolaris) feeding. TPBs secrete saliva during feeding to facilitate the piercing into plant tissues. More importantly, the enzyme-rich saliva may be used for extra-oral digestion and for overcoming plant defense before the plant juice is sucked up by TPBs. To identify salivary gland genes for potential development of novel control strategies, mRNA was extracted from TPB salivary glands and cDNA library clones were sequenced. A de novo-assembling of 7,000 Sanger sequences revealed 666 high quality unique cDNAs with an average size of 624 bp, in which the identities of 347 cDNAs (52%) were determined using Blast2GO. KEGG analysis indicated that these genes participate in eighteen metabolic pathways. Identifications of large number of enzyme genes in TPB salivary glands evidenced functions for extra-oral digestion and feeding damage mechanism, including 45 polygalacturonase, two a-amylase, one glucosidase, one glycan enzyme, one aminopeptidase, four lipase, and many serine protease cDNAs. The presence of multiple transcripts, multigene members, and high abundance of cell wall degradation enzymes (polygalacturonases) indicated that the enzyme-rich saliva may cause damages to plants by breaking down plant cell walls to make nutrients available for feeding. This may also facilitate microbial colonization of the plant. We also identified genes potentially involved in insect adaptation and detoxifying xenobiotics that may allow insects to overcome plant defense responses, including four glutathione S-transferases, three esterases, one cytochrome P450, and several serine proteases. The gene profiles of tarnished plant bug salivary glands revealed in this study provides a foundation for further understanding and potential development of novel enzymatic inhibitors, or other RNAi approaches that may interrupt or minimize TPB feeding damage.