Abstract

Plants employ a diverse set of defense mechanisms to mediate interactions with insects and fungi. These relationships can leave lasting impacts on host plant genome structure such as rapid expansion of gene families through tandem duplication. These genomic signatures provide important clues about the complexities of plant/biotic stress interactions and evolution. We used a pseudo‐backcross hybrid family to identify quantitative trait loci (QTL) controlling associations between Populus trees and several common Populus diseases and insects. Using whole‐genome sequences from each parent, we identified candidate genes that may mediate these interactions. Candidates were partially validated using mass spectrometry to identify corresponding QTL for defensive compounds. We detected significant QTL for two interacting fungal pathogens and three insects. The QTL intervals contained candidate genes potentially involved in physical and chemical mechanisms of host–plant resistance and susceptibility. In particular, we identified adjoining QTLs for a phenolic glycoside and Phyllocolpa sawfly abundance. There was also significant enrichment of recent tandem duplications in the genomic intervals of the native parent, but not the exotic parent. Tandem gene duplication may be an important mechanism for rapid response to biotic stressors, enabling trees with long juvenile periods to reach maturity despite many coevolving biotic stressors.

Highlights

  • In natural ecosystems, the dynamics of plant interactions with other living organisms are complex

  • Binary presence of the canker symptoms caused by S. musiva (Figure 5a) was found to be associated with a quantitative trait loci (QTL) located on Chr16

  • The goal of our research was to utilize QTL analysis as a tool to identify regions of the Populus genome that were important in mediating biotic interactions

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Summary

| INTRODUCTION

The dynamics of plant interactions with other living organisms are complex. In plant–fungal systems breeding for dominant resistance in cereal crops resulted in new selective forces that increased virulent gene frequencies in Puccinia spp. cereal rusts (Chen, 2005; Pretorius, Singh, Wagoire, & Payne, 2000) This in turn can lead to an evolutionary arms race between plants, insects, and fungi with the continual development of mechanisms to overcome both genetic defenses and virulent attacks (Bergelson, Kreitman, Stahl, & Tian, 2001; Thompson & Burdon, 1992). Analyzing how the genome is structured in the host plant when it associates with fungi and insects is important for studying these relationships and understanding the complexities of their genetic interactions Given their rapid growth and vegetative reproduction, Populus species have become a focus for research into biofuel production making them a valuable commercial crop (Meilan et al, 2002; Stanton, Neale, & Li, 2010; Taylor, 2002).

| METHODS
Findings
| DISCUSSION
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