The presence of volatile compounds can provide information about environmental conditions, and some plants can recognize and respond to such volatile compounds in ways that helps maximize their fitness.  For example, volatiles associated with physical damage to leaf tissue seem to reveal the presence of a wounding threat in nearby unwounded leaves, which can then prime themselves for future damage.  Recognition of a threat by airborne volatiles allows preparations for defense at the molecular level without necessarily dedicating resources to a defense phenotype until necessary, which allows unwounded plants to get a leg up in activating a defensive phenotype should a threat arise.  However, there are a number of critical questions related to the signal specificity and source of volatile compounds; and the molecular basis of priming is not well understood.   This talk will address these questions by describing a collection of independent experiments conducted across a series of systems, though the main focus of the work will use the Populus model system.    

Results/Conclusions

           Populus modifies a set of genes in response to z-3-hexenyl acetate exposure that includes a transporter gene for jasmonic acid synthesis and key genes in the shikimate and phenylpropanoid pathways.  More importantly, the collection of genes that are differentially regulated by Populus is unique depending on whether the leaves are exposed to a terpene volatile or a green leaf volatile.  This the balance of this differential regulation may allow for flexibility in the response of Populus to a volatile bouquet.   Indeed, volatile bouquets are more realistic in nature than are individual compounds.  In that context,  I tested whether Populus could differentiate between its own herbivore induced volatile blend versus blends from unrelated plant species (e.g., maize and soybean).  Interestingly, Populus leaves were primed by the Populus volatile bouquet, but also by the maize herbivore-induced plant volatiles.   This indicates that context may be based on the recognition of individual volatile compounds that have unique signaling capacity within the blends.  I will discuss this result with particular focus to the ongoing debate about the ecological relevance to plants for detecting and responding to volatile compounds.