Molecular regulation of defense responses in Picea abies.
In Europe, Norway spruce (Picea abies) is one of the most important conifer species both ecologically and economically. Norway spruce timber is used in building and for pulping. The major pathogen on P. abies in Scandinavia is the root-rot fungus Heterobasidion spp. In mature Norway spruce trees the fungus usually cause stem rot and reduced growth, normally only seedlings and young trees will die as a result of infection but the economical losses due to stem rot are significant.
I am interested in the induced defense responses in P. abies. The general knowledge about induced defence responses and their signaling pathways are primarily derive from studies in model plants (primarily A. thaliana). The current knowledge about induced defense responses in conifers suggests broad similarities to those described in angiosperms, but detailed knowledge are missing. I am involved in several projects which aim to improve the understanding of induced defense responses in P. abies.
- A QTL-mapping project QTLs for resistance to Heterobasidion spp. A full-sib family of P. abies have been tested for susceptibility to Heterobasidion spp. We are collaborating with Professor Ulf Lagercranz at Uppsala University around the construction of a genetic map on this full-sib family. The genetic map will be based primarily on SNP- and SSR-markers. We plan to use markers co-segregating with resistance QTLs, after validation, as markers in practical breeding for better future forest trees.
- A project aiming to identify key processes in resistance reactions in P. abies by use of cDNA-AFLP screening for differentially expressed genes. This project is part of Jenny Arnerups thesis work. We have identified processes specifically induced in bark upon colonization by H. parviporum, these processes have been verified by a qPCR study of different material, leading up to new and interesting questions on how the defense signaling is mediated in P. abies which will be explored in the study of candidate processes described further down.
- A transcriptome analysis of the molecular defense responses in trees with known field resistance after inoculation with Heterobasidion spp. or wounding, this analysis is done in combination with a profiling of the chemical defence responses in the material (by our collaborators at the Department of Chemical Ecology, KTH).We hope that this will allow us to look more closely at the regulation of secondary metabolism in response to Heterobasidion spp. infection.
- Functional analyses of candidate processes for resistance in P. abies. This project will be carried out in collaboration with Prof. Sara von Arnolds group. We plan to study key elements of putative candidate processes in P. abies defense by manipulation of the expression of key enzymes by RNAi or overexpression in transgenic P. abies plants. The effect on susceptibility will be evaluated both as a vitality score of young somatic embryo-plants and by histological observations using WT and GFP-tagged isolates of Heterobasidion.
These projects are financed by SSF, KK-stiftelsen, Formas and the Department
Molecular control of the formation of arbuscular mycorrhiza in Medicago truncatula
This project will focus on the mycorrhization process in the forage legume Medicago truncatula that has become the model plant of choice to study mutualistic plant-microbe interactions. In this species saprophytic, pathogenic, nitrogen-fixing and mycorrhizal interactions can be studied in the same host species. colonization by arbuscular mycorrhiza (AM) forming fungi of the host roots involves a series of events that are tightly regulated by both partners. Recognition and the subsequent initiation of the symbiotic program in the AM fungus and host plant could be described as a compatibility and is genetically predetermined. Throughout the life cycle, from successful colonization of the root cortex to the subsequent formation of new fungal spores, signals must be exchanged between the symbiotic partners inducing developmental stage-specific patterns of gene expression in the host roots and the AMF.
During my postdoctoral stay in Thomas Bollers group at Basel and through my collaboration with Dr. Nadja Feddermann, dr. Peter Salzer and Prof. Boller, we have shown that the expression of a M. truncatula gene Mtchit3-3 is expressed specifically in cells with arbuscles but that an over expression of Mtchit3-3 did not affect the morphology of the arbuscles. We have also studied how the expression of Mtchit3-3 and nearly twenty other mycorrhiza-specific or associated genes are affected by the colonizing fungal identity M. truncatula plants were inoculated with three different AM fungi (Glomus intraradices, Glomus mosseae and Scutellospora castanea). These fungi have different colonization rates and morphologically different colonization patterns. The results showed that the expression of most mycorrhiza associated genes was not linked to colonization rates or nutrient uptake into the plant, but morphologically different AM led to different expression levels of the studied genes. The expression of certain genes associated with arbuscules-type, while others showed higher expression in interactions with AM fungi predominately forming coils in M. truncatula. This created an interest in functional diversity where I now study the effects of several native AM fungal isolates on gene expression in M. truncatula.
This project is financed by VR, FORMAS and Carl Tryggers Stiftelse