Biomarker genes highlight intraspecific and interspecific variations in the responses of Pinus taeda L. and Pinus radiata D. Don to Sirex noctilio F. acid gland secretions

J M Bordeaux,J F D Dean,W W Lorenz

doi:10.1093/treephys/tps091

Abstract

Sirex noctilio F., a Eurasian horntail woodwasp recently introduced into North America, oviposits in pines and other conifers and in the process spreads a phytopathogenic fungus that serves as a food source for its larvae. During oviposition the woodwasp also deposits mucus produced in its acid (venom) gland that alters pine defense responses and facilitates infection by the fungus. A 26,496-feature loblolly pine cDNA microarray was used to survey gene expression of pine tissue responding to S. noctilio venom. Six genes were selected for further assessment by quantitative real-time polymerase chain reaction (qRT-PCR), including one that encoded an apparent PR-4 protein and another that encoded a thaumatin-like protein. Expression of both was strongly induced in response to venom, while expression of an apparent actin gene (ACT1) was stable in response to the venom. The pattern of gene response was similar in Pinus taeda L. and Pinus radiata D. Don, but the magnitude of response in P. radiata was significantly stronger for each of the induced genes. The magnitude of the biomarker gene response to venom also varied according to genotype within these two species. The qRT-PCR assay was used to demonstrate that the primary bioactive component in S. noctilio venom is a polypeptide.

Highlights

The Eurasian horntail woodwasp, Sirex noctilio Fabricius (Hymenoptera: Siricidae), an invasive insect recently introduced into North America, represents a serious economic and ecological threat to pine forests throughout the USA and Canada (Borchert et al 2007)
The large proportion of escapes in assays using seedlings led us to consider that genetic differences between species and among individual genotypes could be confounding bioassays based on observable phenotypic changes
Several researchers have in the past used pine tissue explants in bioassays to gauge the response of pines to attack by S. noctilio (Coutts 1969a, 1969b, 1970, Bowling et al 1970, Fong and Crowden 1973, Spradbery 1973, Kile et al 1974, Wong and Crowden 1976)

Summary

Introduction

The Eurasian horntail woodwasp, Sirex noctilio Fabricius (Hymenoptera: Siricidae), an invasive insect recently introduced into North America, represents a serious economic and ecological threat to pine forests throughout the USA and Canada (Borchert et al 2007). S. noctilio is a major pest when introduced as an exotic into commercial pine plantations of the southern hemisphere (Talbot 1977). These southern hemisphere pine plantations are typically stocked with North American pine species, mostly Monterey Don) and loblolly pines (Pinus taeda L.), which highlights the danger this woodwasp may pose for North American forests (Ciesla 2003)

Methods

Results

Discussion

Conclusion