Characterizing the molecular interface of co-evolved antagonism between host plants and gall insects
Plant Biology Seminar Series

Abstract:
Galls are tumor-like plant growths induced by the stimulus of another organism, from bacteria to fungi to insects. Insect galls are the most complex, and thousands of galling insect species rely on host plants to complete their parasitic life cycle. To accomplish this, insects must manipulate growth and development pathways that span the whole plant genome. However, we are only beginning to understand the complexities of these tightly co-evolved interactions. Galls therefore present a fascinating frontier for studying ecology and molecular biology at the plant-insect interface.

In this seminar, I will present research on two different plant-insect gall interactions: first, the chemical ecology of tall goldenrod (Solidago altissima) and the goldenrod gall fly (Eurosta solidaginis), where goldenrod can detect the volatile sex pheromone of male gall flies. Our central question treated the role of environmental chemical cues in plant defense: since goldenrod can detect the gall fly pheromone, a reliable cue that an imminent threat is nearby, could that information prime the plant to defend itself against any herbivore, not just a co-evolved galler? We found that prior exposure to the fly pheromone resulted in transcriptome-wide temporal changes in defense gene expression in goldenrod when it was damaged by corn earworm (Helicoverpa zea), an herbivore with no co-evolved relationship to S. altissima.

Second, I will discuss the story of cruciferous vegetables (Brassica oleracea vars.) and the invasive Eurasian swede midge (Contarinia nasturtii). We investigated the chemical and molecular response of three B. oleracea crops to swede midge feeding: broccoli (B. oleracea var. italica), cabbage (var. capitata), and collards (var. acephala), which represent three major lineages of B. oleracea domestication. We analyzed phytohormone content and gene expression from swede midge-damaged tissue across 9 days of infestation. We have identified differentially expressed genes involved in salicylic acid biosynthesis and defense, cell wall construction, antixenosis, and nutrient transport, which point to modes of resistance to the insect. Our combined phytohormone and transcriptome analyses will shed much-needed light on the response of Brassica crops to this emerging pest.

About the Speaker:
Robert Witkowski is a fifth-year PhD candidate advised by Dr. Tanya Renner and Dr. John Tooker. He earned his B.S. in Plant Biology from the University of Nebraska-Lincoln. A key NSF Research Experience for Undergraduates position in college opened his eyes to the marvelous diversity of plant evolution. Since then, Robert has explored the evolution of plants alongside insects as natural enemies, especially in the case of insect-induced galls. His dissertation research has focused on the interface of plants and parasitic galling insects, employing methods in chemical ecology, bioinformatics, and imaging to understand this complex interaction. Robert is now a USDA NIFA Predoctoral Fellow studying host resistance against the invasive swede midge, a Eurasian gall pest of broccoli, cabbage, and other cruciferous vegetables.

Contact

  Tanya Renner
  trenner@psu.edu