Expression Profiles of Digestive Genes in the Gut and Salivary Glands of Tarnished Plant Bug (Hemiptera: Miridae)

Abstract

Host plant preference of agricultural pests may shift throughout the growing season, allowing the pests to persist on wild hosts when crops are not available. Lygus Hahn (Hemiptera: Miridae) bugs are severe pests of cotton during flowering and fruiting stages, but can persist on alternative crops, or on weed species. Diversity of digestive enzymes produced by salivary glands and gut tissues play a pivotal role in an organism's ability to utilize various food sources. Polyphagous insects produce an array of enzymes that can process carbohydrates, lipids, and proteins. In this study, the digestive enzyme repertoire of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), was identified by high-throughput sequencing followed by cDNA cloning and sequencing. This study identified 87 digestive genes, including 30 polygalacturonases (PG), one β-galactosidase, three α-glucosidases, six β-glucosidases, 28 trypsin-like proteases, three serine proteases, one apyrase-like protease, one cysteine protease, 12 lipases, and two transcripts with low similarity to a xylanase A-like genes. RNA-Seq expression profiles of these digestive genes in adult tarnished plant bugs revealed that 57 and 12 genes were differentially expressed in the salivary gland and gut (≥5-fold, P ≤ 0.01), respectively. All polygalacturonase genes, most proteases, and two xylanase-like genes were differentially expressed in salivary glands, while most of the carbohydrate and lipid processing enzymes were differentially expressed in the gut. Seven of the proteases (KF208689, KF208697, KF208698, KF208699, KF208700, KF208701, and KF208702) were not detected in either the gut or salivary glands.

Keywords: RNA-Seq; digestive enzyme; expression profile; salivary gland; tarnished plant bug.

Fig. 1.

Evolutionary relationships between putative polygalacturonase (PG) peptide sequences of Lygus lineolaris and those from other mirid species. Neighbor-joining evolutionary tree generated using Mega 10.0.05 program included PG polypeptide sequences of Lygus hesperus and Apolygus lucorum along with the PG genes from fungal species Aspergillus nomus, Neofusicoccum parvum, and Diplodia seriata as the outgroup. A PG sequence from Brassica napa was used to root the evolutionary tree. PG transcripts identified in this study are marked with a blue dot. Branch colors indicate the PGs grouped together due to high sequence similarity.

Fig. 2.

Evolutionary relationships between putative glucosidase peptide sequences of Lygus lineolaris and those from other insect species available in public databases. Neighbor-joining tree generated using Mega 10.0.05 program included various carbohydrate processing gene sequences from Acyrthosyphon pisum, Apis mellifera, Bemisia tabaci, Cimex lectularius, Creontiades dilutes, Chrysomela lapponica, Neotermis koshunensis, Nilaparvata lugens, Pristhesancus plagipennis, Periplenata americana, Riptorus pedestris, Solenopsis invicta, Tribolium castaneum, and Zootermis nevadensis. Carbohydrate processing gene transcripts identified in this study are marked with a blue open circle.

Fig. 3.

Evolutionary relationships between putative protease peptide sequences of Lygus lineolaris and those from other hemipteran species. Neighbor-joining tree generated using Mega 10.0.05 program included various protease gene sequences available in public databases from the following species: Cimex lectularius, Creontiades dilutes, Halyomorpha halys, Lygus lineolaris, Lygus hesperus, Pristhesancus plagipennis. A trypsin sequence from Heliothis virescens was used as the out group. Protease gene transcripts identified in this study are marked with a blue dot.

Fig. 4.

Evolutionary relationships between putative lipase peptide sequences of Lygus lineolaris and those from other mirid species and those from other insect species. Neighbor-joining tree generated using Mega 10.0.05 program included various lipase gene sequences available in public databases from the following species: Acromyrmex echinatior, Acyrthosyphon pisum, Aedes aegypti, Athalia rosae, Bombyx mori, Camponotus floridanus, Habropoda laboriosa, Halyomorpha halys, Harpegnathos saltator, Lygus hesperus, Monomorium pharaonis, Nasonia vitripennis, and Ooceraea biroi. A Lipase sequence from Daphnia pulex was used as the out group. Processing gene transcripts identified in this study are marked with a blue open circle.

Fig. 5.

Log base 2 expression levels of polygalacturonase gene transcripts in the gut and salivary glands of Lygus lineolaris generated from RNA-Seq reads mapped to the transcripts. Standard deviation for each expression level is shown.

Fig. 6.

Log base 2 expression levels of carbohydrate processing gene transcripts in the gut and salivary glands of Lygus lineolaris generated from RNA-Seq reads mapped to the transcripts. Standard deviation for each expression level is shown.

Fig. 7.

Log base 2 expression levels of xylanase-like gene transcripts in the gut and salivary glands of Lygus lineolaris generated from RNA-Seq reads mapped to the transcripts. Standard deviation for each expression level is shown.

Fig. 8.

Log base 2 expression levels of protease gene transcripts in the gut and salivary glands of Lygus lineolaris generated from RNA-Seq reads mapped to the transcripts. Standard deviation for each expression level is shown.

Fig. 9.

Log base 2 expression levels of lipid processing gene transcripts in the gut and salivary glands of Lygus lineolaris generated from RNA-Seq reads mapped to the transcripts. Standard deviation for each expression level is shown.