title: Nucleocytoplasmic trafficking is essential for BAK1- and BKK1-mediated cell-death control.
abstract: BRI1-ASSOCIATED KINASE 1 (BAK1) was initially identified as a co-receptor of the brassinosteroid (BR) receptor BRI1. Genetic analyses also revealed that BAK1 and its closest homolog BAK1-LIKE 1 (BKK1) regulate a BR-independent cell-death control pathway. The double null mutant bak1 bkk1 displays a salicylic acid- and light-dependent cell-death phenotype even without pathogen invasion. Molecular mechanisms of the spontaneous cell death mediated by BAK1 and BKK1 remain unknown. Here we report our identification of a suppressor of bak1 bkk1 (sbb1-1). Genetic analyses indicated that cell-death symptoms in a weak double mutant, bak1-3 bkk1-1, were completely suppressed by the loss-of-function mutation in SBB1, which encodes a nucleoporin (NUP) 85-like protein. Genetic analyses also demonstrated that individually knocking out three other nucleoporin genes from the SBB1-located sub-complex was also able to rescue the cell-death phenotype of bak1-3 bkk1-1. In addition, a DEAD-box RNA helicase, DRH1, was identified in the same protein complex as SBB1 via a proteomic approach. The drh1 mutation also rescues the cell-death symptoms of bak1-3 bkk1-1. Further analyses indicated that export of poly(A)(+) RNA was greatly blocked in the nup and drh1 mutants, resulting in accumulation of significant levels of mRNAs in the nuclei. Over-expression of a bacterial NahG gene to inactivate salicylic acid also rescues the cell-death phenotype of bak1-3 bkk1-1. Mutants suppressing cell-death symptoms always showed greatly reduced salicylic acid contents. These results suggest that nucleocytoplasmic trafficking, especially of molecules directly or indirectly involved in endogenous salicylic acid accumulation, is critical in BAK1- and BKK1-mediated cell-death control.
authors.affiliation: Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.|College of Agronomy, Sichuan Agricultural University, Chengdu, 611130, China.
authors.forename: Junbo
authors.initials: J
authors.lastname: Du
authors.affiliation: Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Yanyan
authors.initials: Y
authors.lastname: Zhan
authors.affiliation: Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Shasha
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Yujun
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: College of Life Sciences, Inner Mongolia Agricultural University, Hohhot, 010018, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Zou
authors.affiliation: Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Kai
authors.initials: K
authors.lastname: He
authors.affiliation: Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Gou
authors.affiliation: College of Life Sciences, Inner Mongolia Agricultural University, Hohhot, 010018, China.
authors.forename: Guojing
authors.initials: G
authors.lastname: Li
authors.affiliation: Ministry of Education Key Laboratory of Bio-Resource and Eco-Environment, College of Life Sciences, Sichuan University, Chengdu, 610064, China.
authors.forename: Honghui
authors.initials: H
authors.lastname: Lin
authors.affiliation: Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China.
authors.forename: Jia
authors.initials: J
authors.lastname: Li
mesh_terms: D021581:Active Transport, Cell Nucleus; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000166:cytology / Q000235:genetics* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D016923:Cell Death; D002467:Cell Nucleus / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D008954:Models, Biological; D009154:Mutation; D028861:Nuclear Pore Complex Proteins / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D018515:Plant Leaves / Q000166:cytology / Q000235:genetics / Q000502:physiology; D030821:Plants, Genetically Modified; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D040901:Proteomics; D012316:RNA Nucleotidyltransferases / Q000235:genetics / Q000378:metabolism*; D020156:Salicylic Acid / Q000378:metabolism / Q000494:pharmacology*; D036226:Seedlings / Q000166:cytology / Q000235:genetics / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; C113103:DRH1 protein, Arabidopsis; D028861:Nuclear Pore Complex Proteins; C000613186:SBB1 protein, Arabidopsis; D011494:Protein Kinases; C570517:SERK4 protein, Arabidopsis; C463660:BAK1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; D012316:RNA Nucleotidyltransferases; D000251:Adenosine Triphosphatases; D020156:Salicylic Acid
keywords: Arabidopsis thaliana; BAK1; BKK1; cell death; nucleoporin; receptor-like kinase