Abstract
Polygalacturonase (PG) is an enzyme in the salivary glands of piercing-sucking mirid bugs (Hemiptera: Miridae) that plays a key role in plant feeding and injury. By constructing a full-length cDNA library, we cloned and characterized 14 PG genes from the salivary glands of Apolygus lucorum, a pestiferous mirid bug in cotton, fruit trees and other crops in China. BLAST search analysis showed that the amino acid sequences deduced from transcripts of the PG genes were closely related to PGs from other mirid bugs. Phylogenetic analysis showed that the PGs of mirid bugs had six main branches, PG1-PG6 (Genbank accession numbers: KF881899~KF881912). We investigated the mRNA expression patterns of the A. lucorum PG genes using real-time PCR. All 14 PGs were expressed significantly higher in the salivary glands than in other tissues (head, thorax, abdomen, leg and wing). For eggs and nymphs, the expression levels of these PGs were much higher in the 5th instar stage than in the egg, and 1st and 3rd instar stages. The PG expression levels in 1-day-old adults were very low, and increased in 5, 20 and 30-day-old adults. Additionally, PG expression levels were generally similar between males and females. The possible physiological functions of PGs in A. lucorum were discussed.
Highlights
The mirid bug Apolygus lucorum (Meyer-Dür) (Hemiptera: Miridae) is a polyphagous insect pest with more than 150 described host plants [1,2]
A normalized salivary gland cDNA library was constructed for A. lucorum via the DSN normalization method combined with the SMART technique according to the manufacturer’s instructions
The function of PG proteins in mirid bugs has been widely studied, and to date, the complete cDNA sequences of several PGs have been cloned from Lygus lineolaris using Expressed Sequenced Tags [14]
Summary
The mirid bug Apolygus lucorum (Meyer-Dür) (Hemiptera: Miridae) is a polyphagous insect pest with more than 150 described host plants [1,2]. As its stylet penetrates (probes), saliva containing several digestive enzymes is introduced into the target tissues in a "lacerate and flush" action [2,5,6]. This type of feeding damages plants and is responsible for the stunting, abscission of squares and bolls (in cotton), and fruit malformation of plants [2,7]. The mechanisms of the formation of plant injury elicited by A. lucorum feeding, especially the role of its salivary enzymes in this physiological process, have not yet been determined
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