Identification and characterization of genes encoding small secreted proteins of Norway spruce pathogen (Heterobasidion parviporum)

Heterobasidion annosum sensu lato (s.l.), as a species complex containing H. annosum sensu stricto (s.s.), H. parviporum and H. abietinum, is necrotrophic pathogen responsible for root and butt rot in pine, spruce and fir respectively in Europe. In Heterobasidion-conifer interaction, the fungus is believed to deploy a repertoire of small secreted proteins (SSP), including known effector proteins, to promote the infection of the host and sustain the disease development. Recent analysis of the H. parviporum genome sequence has revealed the presence of 759 secretom genes. Since H. parviporum and its host are not yet amenable to functional genetic manipulation, heterologous delivery-expression system such as Agrobacterium–Nicotiana benthamiana have been used currently to gain insight into effector functional genomics and assess putative interaction partners. Two candidate genes encoding HpSSPs in the transient expression reveals their ability to induce cell death in N. benthamiana. In particular, HpSSP35.8 could induce a rapid, strong and consistent cell death at 2 day post-infiltration. Thus HpSSP35.8 is regarded as a prime candidate for future functional studies. The expression level of host-defense-related genes in N. benthamiana is further studied under control of HpSSP35.8. Gene expression profiling of HpSSPs is monitored by using qPCR during infection between H. parviporum and Norway spruce seedling roots, highlighting candidates for future function analysis.