Transcriptome-wide gene expression analysis of three ash species using RNA-Seq

Ash trees (Fraxinus spp.) are widely spread throughout eastern North America and represent an important tree species in urban landscape and natural settings. Since the accidental introduction of the invasive insect pest emerald ash borer (EAB; Agrilus planipennis Fairmaire) millions of ash trees have been killed by this devastating pest. However, in Asia, EAB’s natural habitat, the damage to native ash is isolated and only observed in trees under stressed conditions, indicating some level of resistance presumably due to a shared co-evolutionary history. Despite significant efforts directed to contain EAB, it continues to spread through the eastern United States and parts of Canada, threatening the survival of the entire ash genus. Despite this high impact status of EAB, there is little information available at the molecular level for any Fraxinus species. Fundamental molecular knowledge on both susceptible and resistant ash could provide the tools to mitigate the EAB invasion. In this study, constitutive gene expression profiles among susceptible black (Fraxinus nigra) and green ash (F. pennsylvanica), and resistant Manchurian ash (F. mandshurica) were compared using RNA-Seq on an Illumina platform. Several transcripts potentially involved in response to stress were differentially expressed. The expression patterns were validated with the use of real time quantitative PCR (RTqPCR). The information obtained in this study can be of great importance in future ash breeding programs.