Mobile Host mRNAs Are Translated to Protein in the Associated Parasitic Plant Cuscuta campestris

Abstract

<i>Cuscuta</i> spp. are obligate parasites that connect to host vascular tissue using a haustorium. In addition to water, nutrients, and metabolites, a large number of mRNAs are bidirectionally exchanged between <i>Cuscuta</i> spp. and their hosts. This trans-specific movement of mRNAs raises questions about whether these molecules function in the recipient species. To address the possibility that mobile mRNAs are ultimately translated, we built upon recent studies that demonstrate a role for transfer RNA (tRNA)-like structures (TLSs) in enhancing mRNA systemic movement. <i>C. campestris</i> was grown on <i>Arabidopsis</i> that expressed a &beta;-glucuronidase (<i>GUS</i>) reporter transgene either alone or in <i>GUS-tRNA</i> fusions. Histochemical staining revealed localization in tissue of <i>C. campestris</i> grown on <i>Arabidopsis</i> with <i>GUS-tRNA</i> fusions, but not in <i>C. campestris</i> grown on <i>Arabidopsis</i> with <i>GUS</i> alone. This corresponded with detection of <i>GUS</i> transcripts in <i>Cuscuta</i> on <i>Arabidopsis</i> with <i>GUS-tRNA</i>, but not in <i>C. campestris</i> on <i>Arabidopsis</i> with <i>GUS</i> alone. Similar results were obtained with <i>Arabidopsis</i> host plants expressing the same constructs containing an endoplasmic reticulum localization signal. In <i>C. campestris</i>, GUS activity was localized in the companion cells or phloem parenchyma cells adjacent to sieve tubes. We conclude that host-derived <i>GUS</i> mRNAs are translated in <i>C. campestris</i> and that the TLS fusion enhances RNA mobility in the host-parasite interactions.