Journal
PLANT JOURNAL
Volume 80, Issue 4, Pages 683-694Publisher
WILEY-BLACKWELL
DOI: 10.1111/tpj.12662
Keywords
Cucurbita maxima; small RNA binding protein; phloem; systemic silencing; stable ribonucleoprotein complex; protein kinase; phosphatase
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Funding
- National Science Foundation [IOS-0918433]
- United States Department of Agriculture National Institute of Food and Agriculture [201015479]
- Waters Center of Innovation (Milford, MA, USA)
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In plants, the vascular system, specifically the phloem, functions in delivery of small RNA (sRNA) to exert epigenetic control over developmental and defense-related processes. Although the importance of systemic sRNA delivery has been established, information is currently lacking concerning the nature of the protein machinery involved in this process. Here, we show that a PHLOEM SMALL-RNA BINDING PROTEIN 1 (PSRP1) serves as the basis for formation of an sRNA ribonucleoprotein complex (sRNPC) that delivers sRNA (primarily 24nt) to sink organs. Assembly of this complex is facilitated through PSRP1 phosphorylation by a phloem-localized protein kinase, PSRPK1. During long-distance transport, PSRP1-sRNPC is stable against phloem phosphatase activity. Within target tissues, phosphatase activity results in disassembly of PSRP1-sRNPC, a process that is probably required for unloading cargo sRNA into surrounding cells. These findings provide an insight into the mechanism involved in delivery of sRNA associated with systemic gene silencing in plants.
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