Abstract
Cuscuta 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 Cuscuta 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. C. campestris was grown on Arabidopsis that expressed a β-glucuronidase (GUS) reporter transgene either alone or in GUS-tRNA fusions. Histochemical staining revealed localization in tissue of C. campestris grown on Arabidopsis with GUS-tRNA fusions, but not in C. campestris grown on Arabidopsis with GUS alone. This corresponded with detection of GUS transcripts in Cuscuta on Arabidopsis with GUS-tRNA, but not in C. campestris on Arabidopsis with GUS alone. Similar results were obtained with Arabidopsis host plants expressing the same constructs containing an endoplasmic reticulum localization signal. In C. campestris, GUS activity was localized in the companion cells or phloem parenchyma cells adjacent to sieve tubes. We conclude that host-derived GUS mRNAs are translated in C. campestris and that the TLS fusion enhances RNA mobility in the host-parasite interactions.
Highlights
Cuscuta spp. are holoparasitic plants that attack a broad range of hosts, and are capable of causing substantial agricultural losses [1]
We address two central questions: (1) Does a transfer RNA (tRNA) fusion system that confers cellcell mobility on GUS gene mRNAs in Arabidopsis enable it to traffic into C. campestris? (2) Is such a mobile GUS mRNA translated into protein in C. campestris? we have found that tRNA fused to the GUS gene facilitates the movement of GUS mRNA and results in GUS enzyme activity in C. campestris haustoria, stems, floral organs, phloem, and apical termini of sieve tubes
We have addressed the question of whether host-encoded mRNA could be translated into a functional protein following translocation into the parasitic plant C. campestris
Summary
Cuscuta spp. (dodders) are holoparasitic plants that attack a broad range of hosts, and are capable of causing substantial agricultural losses [1]. We have found that tRNA fused to the GUS gene facilitates the movement of GUS mRNA and results in GUS enzyme activity in C. campestris haustoria, stems, floral organs, phloem, and apical termini of sieve tubes These results support the idea that the transported GUS-tRNA mRNA from Arabidopsis host plants is translated in C. campestris cells. Plants 2022, 11, 93 hosts expressing GUS-tRNAMet (Figure 1E,F) These results indicate that the presence of tRNA motif promotes mobility of GUS activity from host to C. campestris, similar to its function in Arabidopsis grafting experiments [20]. In further support of this observation, sequential staining for GUS activity, followed by phloroglucinol-HCl staining of lignin in xylem cells [25], indicated that for C. campestris growing on Arabidopsis 35S:GUS-tRNAMet plants the GUS signals were detected more centrally in the C. campestris stem than the lignin staining (Supplemental Figure S2).
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