title: Arabidopsis PUB22 and PUB23 are homologous U-Box E3 ubiquitin ligases that play combinatory roles in response to drought stress.
abstract: Ubiquitination is involved in diverse cellular processes in higher plants. In this report, we describe Arabidopsis thaliana PUB22 and PUB23, two homologous U-box-containing E3 ubiquitin (Ub) ligases. The PUB22 and PUB23 genes were rapidly and coordinately induced by abiotic stresses but not by abscisic acid. PUB22- and PUB23-overexpressing transgenic plants were hypersensitive to drought stress. By contrast, loss-of-function pub22 and pub23 mutant plants were significantly more drought-tolerant, and a pub22 pub23 double mutant displayed even greater drought tolerance. These results indicate that PUB22 and PUB23 function as negative regulators in the water stress response. Yeast two-hybrid, in vitro pull-down, and in vivo coimmunoprecipitation experiments revealed that PUB22 and PUB23 physically interacted with RPN12a, a subunit of the 19S regulatory particle (RP) in the 26S proteasome. Bacterially expressed RPN12a was effectively ubiquitinated in a PUB-dependent fashion. RPN12a was highly ubiquitinated in 35S:PUB22 plants, but not in pub22 pub23 double mutant plants, consistent with RPN12a being a substrate of PUB22 and PUB23 in vivo. In water-stressed wild-type and PUB-overexpressing plants, a significant amount of RPN12a was dissociated from the 19S RP and appeared to be associated with small-molecular-mass protein complexes in cytosolic fractions, where PUB22 and PUB23 are localized. Overall, our results suggest that PUB22 and PUB23 coordinately control a drought signaling pathway by ubiquitinating cytosolic RPN12a in Arabidopsis.
authors.affiliation: Department of Biology, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea.
authors.forename: Seok Keun
authors.initials: SK
authors.lastname: Cho
authors.forename: Moon Young
authors.initials: MY
authors.lastname: Ryu
authors.forename: Charlotte
authors.initials: C
authors.lastname: Song
authors.forename: June M
authors.initials: JM
authors.lastname: Kwak
authors.forename: Woo Taek
authors.initials: WT
authors.lastname: Kim
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics / Q000502:physiology; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002850:Chromatography, Gel; D055864:Droughts; D018506:Gene Expression Regulation, Plant; D047468:Immunoprecipitation; D008969:Molecular Sequence Data; D010802:Phylogeny; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques; D044767:Ubiquitin-Protein Ligases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D029681:Arabidopsis Proteins; C455510:RPN12 protein, Arabidopsis; C582896:PUB22 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases