title: The Hippo/STE20 homolog SIK1 interacts with MOB1 to regulate cell proliferation and cell expansion in Arabidopsis.
abstract: Multicellular organisms co-ordinate cell proliferation and cell expansion to maintain organ growth. In animals, the Hippo tumor suppressor pathway is a master regulator of organ size. Central to this pathway is a kinase cascade composed of Hippo and Warts, and their activating partners Salvador and Mob1/Mats. In plants, the Mob1/Mats homolog MOB1A has been characterized as a regulator of cell proliferation and sporogenesis. Nonetheless, no Hippo homologs have been identified. Here we show that the Arabidopsis serine/threonine kinase 1 (SIK1) is a Hippo homolog, and that it interacts with MOB1A to control organ size. SIK1 complements the function of yeast Ste20 in bud site selection and mitotic exit. The sik1 null mutant is dwarf with reduced cell numbers, endoreduplication, and cell expansion. A yeast two-hybrid screen identified Mob1/Mats homologs MOB1A and MOB1B as SIK1-interacting partners. The interaction between SIK1 and MOB1 was found to be mediated by an N-terminal domain of SIK1 and was further confirmed by bimolecular fluorescence complementation. Interestingly, sik1 mob1a is arrested at the seedling stage, and overexpression of neither SIK1 in mob1a nor MOB1A in sik1 can rescue the dwarf phenotypes, suggesting that SIK1 and MOB1 may be components of a larger protein complex. Our results pave the way for constructing a complete Hippo pathway that controls organ growth in higher plants.
authors.affiliation: Tianjin Key Laboratory of Protein Sciences, Department of Plant Biology and Ecology, College of Life Sciences, Nankai University, Tianjin 300071, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Xiong
authors.affiliation: Tianjin Key Laboratory of Protein Sciences, Department of Plant Biology and Ecology, College of Life Sciences, Nankai University, Tianjin 300071, China.
authors.forename: Xuefei
authors.initials: X
authors.lastname: Cui
authors.affiliation: Tianjin Key Laboratory of Protein Sciences, Department of Plant Biology and Ecology, College of Life Sciences, Nankai University, Tianjin 300071, China.
authors.forename: Xiangrong
authors.initials: X
authors.lastname: Yuan
authors.affiliation: Tianjin Key Laboratory of Protein Sciences, Department of Plant Biology and Ecology, College of Life Sciences, Nankai University, Tianjin 300071, China.
authors.forename: Xiulian
authors.initials: X
authors.lastname: Yu
authors.affiliation: Tianjin Key Laboratory of Protein Sciences, Department of Plant Biology and Ecology, College of Life Sciences, Nankai University, Tianjin 300071, China.
authors.forename: Jialei
authors.initials: J
authors.lastname: Sun
authors.affiliation: Tianjin Key Laboratory of Protein Sciences, Department of Plant Biology and Ecology, College of Life Sciences, Nankai University, Tianjin 300071, China gongq@nankai.edu.cn.
authors.forename: Qingqiu
authors.initials: Q
authors.lastname: Gong
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002452:Cell Count; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism*; D049109:Cell Proliferation; D048429:Cell Size; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D011003:Ploidies; D011485:Protein Binding; D000072417:Protein Domains; D013347:Subcellular Fractions / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C000612157:MOB1B protein, Arabidopsis; C000589223:Mob1A protein, Arabidopsis thaliana
keywords: Arabidopsis thaliana; Hippo; MOB1; SIK1; STE20.; cell division; cell expansion; organ growth