title: Plasmodesmal-associated protein kinase in tobacco and Arabidopsis recognizes a subset of non-cell-autonomous proteins.
abstract: Cell-to-cell communication in plants involves the trafficking of macromolecules through specialized intercellular organelles, termed plasmodesmata. This exchange of proteins and RNA is likely regulated, and a role for protein phosphorylation has been implicated, but specific components remain to be identified. Here, we describe the molecular characterization of a plasmodesmal-associated protein kinase (PAPK). A 34-kD protein, isolated from a plasmodesmal preparation, exhibits calcium-independent kinase activity and displays substrate specificity in that it recognizes a subset of viral and endogenous non-cell-autonomous proteins. This PAPK specifically phosphorylates the C-terminal residues of tobacco mosaic virus movement protein (TMV MP); this posttranslational modification has been shown to affect MP function. Molecular analysis of purified protein established that tobacco (Nicotiana tabacum) PAPK is a member of the casein kinase I family. Subcellular localization studies identified a possible Arabidopsis thaliana PAPK homolog, PAPK1. TMV MP and PAPK1 are colocalized within cross-walls in a pattern consistent with targeting to plasmodesmata. Moreover, Arabidopsis PAPK1 also phosphorylates TMV MP in vitro at its C terminus. These results strongly suggest that Arabidopsis PAPK1 is a close homolog of tobacco PAPK. Thus, PAPK1 represents a novel plant protein kinase that is targeted to plasmodesmata and may play a regulatory role in macromolecular trafficking between plant cells.
authors.affiliation: Section of Plant Biology, Division of Biological Sciences, University of California, Davis, CA 95616, USA. lee@dbi.udel.edu
authors.forename: Jung-Youn
authors.initials: JY
authors.lastname: Lee
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Taoka
authors.forename: Byung-Chun
authors.initials: BC
authors.lastname: Yoo
authors.forename: Gili
authors.initials: G
authors.lastname: Ben-Nissan
authors.forename: Dong-Jin
authors.initials: DJ
authors.lastname: Kim
authors.forename: William J
authors.initials: WJ
authors.lastname: Lucas
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D047389:Casein Kinase I / Q000737:chemistry; D002450:Cell Communication / Q000235:genetics; D017124:Conserved Sequence; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010802:Phylogeny; D031425:Plasmodesmata / Q000201:enzymology* / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D011494:Protein Kinases; C508001:PAPK1 protein, Arabidopsis; D047389:Casein Kinase I