Graduate Student Penn State University State College, Pennsylvania
Body of Abstract: Dodders (Cuscuta spp.) are obligate parasitic plants that rob host plants of water and nutrients via an organ called the haustorium. At the haustorial interface, we discovered that C. campestris delivers microRNAs into the host and manipulates host genes. However, it is largely unknown how these interface-induced microRNAs (IIMs) are made. On every IIM, we identified Upstream Sequence Element, a motif that is absent from all other plant microRNAs. This element is previously described to activate genes by recruiting the protein called Shoot Redifferentiation 2 (SRD2). It is likely that dodder have co-opted the same mechanism to transcribe IIMs. Most microRNAs are processed by the protein called Dicer-like 1 (DCL1). We speculate that DCL1 is also required for producing IIMs. To test this, we generated transgenic Arabidopsis thaliana expressing hairpin RNAs. Feeding on the transgenic hosts, C. campestris takes up the RNAs and its SRD2 and DCL1 are silenced. We successfully reduced parasite DCL1 by 40% within 2 weeks. We are preparing to measure IIMs accumulation upon decreased DCL1, as well as optimizing SRD2 repression. If making interface-induced microRNAs requires SRD2 or DCL1, we should observe a reduction of these microRNAs. The purpose of the study is to understand how the Cuscuta-derived, interface-induced microRNAs are made, and how to shut down their production. This opens the possibility to decline dodder parasitism. Which is important because Cuscuta is listed on USDA’s Top Ten most noxious weeds. We are among the first to deliver RNA interference into Cuscuta using A. thaliana, a plant with rapid life cycle. This allows us to test many parasite genes rapidly and boost the efficiency of Cuscuta research. If it turns out that interface-induced microRNAs production can be shut down, it could point to new ways to combat Cuscuta infestation.