The partial characterisation of the terpene synthase genes implicated in the defence response by Pinus patula and Pinus tecunumanii to Fusarium circinatum

Abstract

Pitch canker, caused by Fusarium circinatum (teleomorph Gibberella circinata), is regarded as one of the most severe phytopathogenic diseases affecting commercial Pinus plantations worldwide, and is anticipated to be aggravated by the increase in temperature and humidity associated with climate change. In South Africa, the preferred commercial pine species has been Pinus patula. The fungus causes Fusarium-wilt on seedlings and has drastically decreased the post-planting survival of seedlings. Hybridisation of P. patula with Fusarium-tolerant species such as Pinus tecunumanii, has led to the development of an alternative planting stock. However, the mechanisms underlying P. tecunumanii’s relative resistance remains inconclusive. Previous research has highlighted the putative involvement of terpene synthases in defence against Fusarium spp., as their regulation is significantly altered early in response to this pathogen. RNA-seq reference transcriptomes for P. patula and P. tecunumanii have provided the much-needed genetic resources necessary to interrogate the putative defence related genes undergoing differential expression due to F. circinatum infection. The aim of this study was to determine whether observed differences in resistance between these two hosts, is correlated with induced terpene synthase gene expression profiles, and to resolve the implicated orthologs. The differential expression patterns of genes identified as terpene synthase orthologs was assessed for their potential to contribute to resistance. While the two host species, P. patula and P. tecunumanii, did appear to respond dissimilarly, this is not indicative of terpene synthesis playing a causal role in defence.