Comparative Transcriptomic Response of Two Pinus Species to Infection with the Pine Wood Nematode Bursaphelenchus xylophilus

Gaspar Gaspar,Meireles Meireles,Costa Costa,Trindade Trindade,Fortes Fortes,Usié Usié,Guimarães Guimarães,Ramos Ramos,Simões Simões

doi:10.3390/f11020204

Abstract

Pine wilt disease (PWD) caused by pine wood nematode (PWN), Bursaphelenchus xylophilus, is a serious threat to global forest populations of conifers, in particular Pinus spp. Recently, the presence of PWN was reported in dead Yunnan pine (Pinus yunnanensis) trees under natural conditions. To further understand the potential impact caused by PWN in Yunnan pine populations, a transcriptional profiling analysis was performed over different time points (0 hours (h), 6 h, 24 h, 48 h, and 7 days) after PWN inoculation. A total of 9961 differentially expressed genes were identified after inoculation, which suggested a dynamic response against the pathogen, with a more intense pattern at 48 h after inoculation. The results also highlighted a set of biological mechanisms triggered after inoculation that provide valuable information regarding the response of Yunnan pine to PWN infection. When compared with maritime pine (Pinus pinaster), the Yunnan pine response was less complex and involved a smaller number of differentially expressed genes, which may be associated with the increased degree of resistance to PWN displayed by Yunnan pine. These results revealed different strategies to cope with PWN infection by these two pine species, which display contrasting degrees of susceptibility, especially in the timely perception of the infection and response magnitude.

Highlights

Pine wilt disease (PWD) is one of the main threats to conifer forests worldwide, being responsible for millions of losses every year
To improve accuracy and robustness, an additional clustering step with CAP3 was applied, which reduced the original number of contigs to 306,164, with a total length of 133,362,131 bp (Table S2 shows a summary of the assembly statistics)
This study provides new insights for the understanding of the molecular response of Yunnan pine to pine wood nematode (PWN) infection, pointing out the defense mechanisms triggered after inoculation

Summary

Introduction

Pine wilt disease (PWD) is one of the main threats to conifer forests worldwide, being responsible for millions of losses every year. Pine wood nematode (PWN), Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle, is the causal agent of PWD. This parasite, native to North America, is considered a quarantine organism by the European and Mediterranean Plant Protection Organization. The PWN transmission between pine trees is carried out by an insect vector, belonging to the Monochamus genus [2]. Nematodes can be transmitted in two ways: (i) through insect-feeding wounds in the bark of healthy trees, known as primary transmission; (ii) by oviposition sites in dead or weakened trees, representing a secondary inoculation way [3]. The pine needles turn brown, the resin flow is suppressed and, the host tree wilts and dies within a few weeks

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