title: Systemic delivery of siRNA in pumpkin by a plant PHLOEM SMALL RNA-BINDING PROTEIN 1-ribonucleoprotein complex.
abstract: 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 24 nt) 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.
authors.affiliation: Department of Plant Biology, College of Biological Sciences, University of California, Davis, CA, 95616, USA.
authors.forename: Byung-Kook
authors.initials: BK
authors.lastname: Ham
authors.forename: Gang
authors.initials: G
authors.lastname: Li
authors.forename: Weitao
authors.initials: W
authors.lastname: Jia
authors.forename: Julie A
authors.initials: JA
authors.lastname: Leary
authors.forename: William J
authors.initials: WJ
authors.lastname: Lucas
mesh_terms: D000595:Amino Acid Sequence; D028464:Cucurbita / Q000235:genetics*; D008969:Molecular Sequence Data; D052585:Phloem / Q000378:metabolism; D010766:Phosphorylation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins
keywords: Cucurbita maxima; phloem; phosphatase; protein kinase; small RNA binding protein; stable ribonucleoprotein complex; systemic silencing