title: SINAT5 promotes ubiquitin-related degradation of NAC1 to attenuate auxin signals.
abstract: The plant hormone indole-3 acetic acid (IAA or auxin) controls many aspects of plant development, including the production of lateral roots. Ubiquitin-mediated proteolysis has a central role in this process. The genes AXR1 and TIR1 aid the assembly of an active SCF (Skp1/Cullin/F-box) complex that probably promotes degradation of the AUX/IAA transcriptional repressors in response to auxin. The transcription activator NAC1, a member of the NAM/CUC family of transcription factors, functions downstream of TIR1 to transduce the auxin signal for lateral root development. Here we show that SINAT5, an Arabidopsis homologue of the RING-finger Drosophila protein SINA, has ubiquitin protein ligase activity and can ubiquitinate NAC1. This activity is abolished by mutations in the RING motif of SINAT5. Overexpressing SINAT5 produces fewer lateral roots, whereas overexpression of a dominant-negative Cys49 --> Ser mutant of SINAT5 develops more lateral roots. These lateral root phenotypes correlate with the expression of NAC1 observed in vivo. Low expression of NAC1 in roots can be increased by treatment with a proteasome inhibitor, which indicates that SINAT5 targets NAC1 for ubiquitin-mediated proteolysis to downregulate auxin signals in plant cells.
authors.affiliation: Laboratory of Molecular Cell Biology, Temasek Life Sciences Laboratory, National University of Singapore, 1 Research Link, 117604 Singapore.
authors.forename: Qi
authors.initials: Q
authors.lastname: Xie
authors.forename: Hui-Shan
authors.initials: HS
authors.lastname: Guo
authors.forename: Geza
authors.initials: G
authors.lastname: Dallman
authors.forename: Shengyun
authors.initials: S
authors.lastname: Fang
authors.forename: Allan M
authors.initials: AM
authors.lastname: Weissman
authors.forename: Nam-Hai
authors.initials: NH
authors.lastname: Chua
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins / Q000737:chemistry / Q000378:metabolism; D017343:Genes, Plant / Q000235:genetics; D007210:Indoleacetic Acids / Q000494:pharmacology*; D008025:Ligases / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011485:Protein Binding; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases
chemical_list: D029681:Arabidopsis Proteins; D029721:Drosophila Proteins; D007210:Indoleacetic Acids; C418004:NAC1 protein, Arabidopsis; D018749:RNA, Plant; C466426:SINAT5 protein, Arabidopsis; D015534:Trans-Activators; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; D008025:Ligases