Transcriptome Analysis of Resistance of Shrub Willow to Empoasca fabae

Shrub Willow (Salix spp.), a short rotation woody biomass crop, has superior properties as a perennial energy crop for the Northeast and Midwest US. The potato leafhopper Empoasca fabae (Harris) is an insect pest that poses a serious threat to shrub willow. Currently used cultivars display varying susceptibility towards potato leafhopper infestation. At present, use of resistant cultivars is the optimal strategy for pest control. However, knowledge of the resistance genes is not available for selection and breeding. In our study, transcriptome analysis using RNA-Seq was conducted on two shrub willow parents (‘94006’ and ‘Jorr’) in a time series (leaf tissue was collected at 0, 6, 24 and 96h after pest challenge). On average, 3.1 million paired-end reads per library were generated on the Illumina Hiseq2500 platform and mapped to the Salix purprea reference genome transcript sequences (Salix purpurea v1.0, DOE-JGI). Analysis revealed that potato leafhopper induced cultivar-specific defense genes, especially in secondary cell wall modification, play an important role in the defense mechanism in a resistant cultivar. In a highly susceptible genotype, genes involved in programed cell death were highly expressed, which explained the pest-derived symptoms like necrosis, leaf curling and early leaf drop on susceptible genotype. This is a first step in identifying resistance genes for resistant to potato leafhopper from genomic resources for shrub willow breeding. This is part of the project The Northeast Woody/Warm-season Biomass Consortium (NEWBio), which is funded by the USDA Agriculture and Food Research Initiative program of the National Institute of Food and Agriculture grant # 2012-68005-19703.