title: Down-regulation of the 26S proteasome subunit RPN9 inhibits viral systemic transport and alters plant vascular development.
abstract: Plant viruses utilize the vascular system for systemic movement. The plant vascular network also transports water, photosynthates, and signaling molecules and is essential for plant growth. However, the molecular mechanisms governing vascular development and patterning are still largely unknown. From viral transport suppressor screening using virus-induced gene silencing, we identified a 26S proteasome subunit, RPN9, which is required for broad-spectrum viral systemic transport. Silencing of RPN9 in Nicotiana benthamiana inhibits systemic spread of two taxonomically distinct viruses, Tobacco mosaic virus and Turnip mosaic virus. The 26S proteasome is a highly conserved eukaryotic protease complex controlling many fundamental biochemical processes, but the functions of many 26S proteasome regulatory subunits, especially in plants, are still poorly understood. We demonstrate that the inhibition of viral systemic transport after RPN9 silencing is largely due to alterations in the vascular tissue. RPN9-silenced plants display extra leaf vein formation with increased xylem and decreased phloem. We further illustrate that RPN9 functions at least in part through regulation of auxin transport and brassinosteroid signaling, two processes that are crucial for vascular formation. We propose that RPN9 regulates vascular formation by targeting a subset of regulatory proteins for degradation. The brassinosteroid-signaling protein BZR1 is one of the targets.
authors.affiliation: Center for Plant Cell Biology, Department of Plant Pathology, University of California, Riverside, California 92521, USA. hailingj@ucr.edu
authors.forename: Hailing
authors.initials: H
authors.lastname: Jin
authors.forename: Songtao
authors.initials: S
authors.lastname: Li
authors.forename: Andy
authors.initials: A
authors.lastname: Villegas
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D015536:Down-Regulation; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D007210:Indoleacetic Acids / Q000378:metabolism; D008969:Molecular Sequence Data; D009029:Mosaic Viruses / Q000502:physiology*; D009068:Movement; D010937:Plant Growth Regulators; D018515:Plant Leaves / Q000033:anatomy & histology / Q000254:growth & development* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000502:physiology* / Q000821:virology*
chemical_list: D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D021122:Protein Subunits; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease