RoL: Control of trans-species microRNA expression

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Parasitic plants can be noxious weeds that attack crops and affect agricultural productivity. The parasitic plant Dodder (genus Cuscuta) is widespread in the United States and is a problem on diverse crops. Strategies to control Dodders are limited. One way that Dodders affect their hosts is by injected short bits of genetic information, "microRNAs", into host stems. These "trans-species" microRNAs destroy certain target host genes. This process seems to allow the parasite to suppress the host's immune system. This project seeks to understand exactly how the Dodder trans-species microRNAs are activated and injected into the host plants. Understanding this process could lead to novel methods of control and thus would benefit agriculture. Other parasites and pathogens use trans-species microRNAs to manipulate their hosts. Thus, details learned from study of the Dodder trans-species microRNAs may inform research into a broader array of parasites and pathogens.Recent studies have shown that Dodder (Cuscuta) expresses many microRNAs which enter host plant tissues and target host mRNAs. These trans-species microRNAs are likely acting as virulence factors to shut down host mRNAs in order to benefit the parasite. Unlike canonical microRNAs, the Cuscuta trans-species microRNAs only accumulate at the interface between the host and parasite. The core promoters upstream of trans-species microRNA loci in the Cuscuta genome all have a common Upstream Sequence Element (USE) that is absent from canonical microRNAs and also absent from the promoters of Cuscuta mRNAs. The 10 base-pair USE sequence is identical to the USE element known to drive transcription of small nuclear RNAs (snRNAs) in all plants. It thus appears that Cuscuta trans-species microRNAs have co-opted a pre-existing, constitutive promoter element to drive a highly tissue-specific expression pattern. This project will seek to understand this process via two aims: Aim 1: Functional analyses of USE to determine its role in the transcription of Cuscuta trans-species microRNA precursors. Aim 2: Identification and functional analyses of the USE-binding factor(s).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.