Forest Investment Account (FIA) - Forest Science Program
FIA Project Y081092

    Development of molecular markers to aid in the identification of western redcedar populations that are resistant to deer browsing and heartwood rot fungi
 
Project lead: Mattsson, Jim (Simon Fraser University)
Author: Mattsson, Jim
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
SIGNIFICANCE Based on total logs harvested, western redcedar (Thuja Plicata; hereafter abbreviated as WRC) ranks as the fifth most important species in BC (1). WRC wood is highly valued for its high dimension stability and its natural durability and is used in many exterior applications. The utilization of WRC is not without problems however. In BC, reforestation with WRC is expensive and inefficient due to extensive herbivory by ungulates, i.e. deer and elk. Currently, the industry spends up to $6 per tree in deer/elk areas, which corresponds to most of the BC coast and part of the interior, in order to establish WRC. Although regarded as highly durable, second growth WRC heartwood succumbs to early rot, especially in the interior cedar/hemlock biogeoclimatic zone, where complete trees are culled. However, substantial tree-to-tree variation among second-growth trees with respect to both ungulate herbivory and heartwood rot resistance has been noted and the BC Ministry of Forests (MoF) is currently breeding for browsing resistance and intends to breed for heartwood rot resistance. Here we are proposing research to develop markers that correlate with browsing resistance and heartwood rot resistance. The intended use of these markers is to substantially shorten the time and cost for each breeding cycle with respect to browsing resistance and, for the first time, enable efficient breeding for rot resistance in WRC. The deployment of such markers could have considerable short-term benefits for reforestation with WRC and invaluable long-term benefit with regard to the quality and reputation of WRC heartwood from BC. BACKGROUND One of us (Dr Russell, MoF) has demonstrated a strong positive correlation between monoterpenoid content in WRC and resistance to ungulate browsing (12). Monoterpenes are a group of 10-carbon terpenoids found in most conifers (3,4). Up to 15 monoterpenes have been identified from WRC needle extracts (5,15). It is known that induced synthesis of monoterpenoids following attack by stem-boring insects is accompanied by a significant up-regulation of monoterpene synthase (mono-TPS) gene expression (4,6). Thus, it is possible to obtain an indirect measure of monoterpenoid content and thereby resistance by quantifying the expression of mono-TPS genes. Another group of terpenoids implicated in plant defense are the tropolones (7). Tropolones are natural fungicides found in the heartwood of mature trees where they are involved in WRC resistance to fungal degradation (7). An early screening tool would be invaluable in rapidly identifying durable, rot-resistant trees for reforestation. PROPOSED RESEARCH The aim of the research is to develop markers for Marker-Assisted Selection (MAS) to be used to select for deer- and heartwood rot-resistant offspring in crosses from WRC breeding programs. Dr. Russell has assessed the needle monoterpene and heartwood tropolone content in 350 WRC clones of wide-spread coastal geographic origins and identified large variations in the content of these compounds (graphs #1 and2). Thus, there is considerable genetic potential for breeding for ungulate herbivory and heartwood rot resistance in WRC. Of especial note, Dr. Russell has found no negative genetic correlations between growth and monoterpene or tropolone content in cloned 10-year-old WRC provenances (graph #3). Thus, there appears to be no or minimal cost in terms of growth attached to high production of these compounds, and therefore no inherent contradiction to introgression of all three traits. Markers for prediction of ungulate herbivory resistance Previous research has shown that there is good correlation between the production of transcripts (mRNAs) from genes encoding mono-TPS and production of the corresponding monoterpenes (4). Our approach is to clone the most abundant mono-TPS mRNAs from trees producing high levels of monoterpenes based on homology to other mono-TPS genes in conifers. Two of us, Drs Mattsson and Plant, have extensive experience of gene cloning, including the cloning of mono-TPS genes in Sitka spruce (6). The isolated mono-TPS cDNAs will be used to correlate expression levels with monoterpene levels so as to identify potential expression markers for predicting ungulate resistance. Both Drs Mattsson and Plant have a published record of gene expression analysis using various methods. This phase of the research will be accompanied by assessment of monoterpenoid content in clones of key WRC parentage by Dr. Gerhard Gries to provide an exact measure of gene expression and monoterpene profiles in the same plants. The next phase of the research is to develop those expression markers that predict deer resistance for large-scale screening. Affordable large-scale screening of gene expression levels has become possible by the recent development of Quantitative Polymerase-Chain-Reaction (Q-PCR), which allows quantification of gene expression in minute samples (< 100 mg) with minimal cost ($2-5/sample). Since the procedure lends itself to bulk processing of many samples in parallel it is time-efficient and ideal for the assessment of resistance in WRC populations via assessment of mono-TPS transcript level. Marker for prediction of heartwood rot resistance Presently, there are three major obstacles to efficient breeding for heartwood rot resistance in WRC: (i) The tropolones that confer resistance accumulate at quantifiable levels in the heartwood of relatively mature trees (> 15 years; 9). (ii) The technology for tropolone extraction and quantification is specialized and does not lend itself to large-scale screening of populations. (iii) The biochemistry and genetics behind tropolone biosynthesis is unknown. Here we propose two independent approaches to this seemingly intractable problem: 1. It is known that high levels of tropolone production can be induced in juvenile WRC material by various elicitors (10). We will assess whether the level of tropolone induction correlates with levels of tropolone accumulation in mature heartwood in clones from different parentages (see methods). If that is the case, it may be possible to predict heartwood rot resistance by screening juvenile material treated with elicitors for high tropolone content. 2. The rapid and reproducible induction of tropolones in WRC cell cultures (10) will facilitate the capture of induced mRNAs some of which are likely to encode enzymes in tropolone biosynthesis. In a first step towards the development of DNA-based MAS for rot resistance, we will use cDNA subtraction followed by DNA sequencing to identify genes with putative functions in tropolone biosynthesis (see methods).
Related projects:  FSP_Y092092FSP_Y103092
Contact: Mattsson, Jim, (778) 782-4291, jmattsso@sfu.ca

    Deliverables:

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Updated August 16, 2010 

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