title: The type 3 effector NopL of Sinorhizobium sp. strain NGR234 is a mitogen-activated protein kinase substrate.
abstract: Pathogenic bacteria utilize type 3 secretion systems to inject type 3 effectors (T3Es) into host cells, thereby subverting host defense reactions. Similarly, T3Es of symbiotic nitrogen-fixing rhizobia can affect nodule formation on roots of legumes. Previous work showed that NopL (nodulation outer protein L) of Sinorhizobium(Ensifer) sp. strain NGR234 is multiply phosphorylated in eukaryotic cells and that this T3E suppresses responses mediated by mitogen-activated protein (MAP) kinase signaling in yeast (mating pheromone signaling) and plant cells (expression of pathogenesis-related defense proteins). Here, we show that NopL is a MAP kinase substrate. Microscopic observations of fluorescent fusion proteins and bimolecular fluorescence complementation analysis in onion cells indicated that NopL is targeted to the nucleus and forms a complex with SIPK (salicylic acid-induced protein kinase), a MAP kinase of tobacco. In vitro experiments demonstrated that NopL is phosphorylatyed by SIPK. At least nine distinct spots were observed after two-dimensional gel electrophoresis, indicating that NopL can be hyperphosphorylated by MAP kinases. Senescence symptoms in nodules of beans (Phaseolus vulgaris cv. Tendergreen) were analyzed to determine the symbiotic effector activity of different NopL variants with serine to alanine substitutions at identified and predicted phosphorylation sites (serine-proline motif). NopL variants with six or eight serine to alanine substitutions were partially active, whereas NopL forms with 10 or 12 substituted serine residues were inactive. In conclusion, our findings provide evidence that NopL interacts with MAP kinases and reveals the importance of serine-proline motifs for effector activity during symbiosis.
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.
authors.forename: Ying-Ying
authors.initials: YY
authors.lastname: Ge
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.
authors.forename: Qi-Wang
authors.initials: QW
authors.lastname: Xiang
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.
authors.forename: Christian
authors.initials: C
authors.lastname: Wagner
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.
authors.forename: Di
authors.initials: D
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou, China Shenzhen Research and Development Center of State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Baoan, Shenzhen, China xiezping@mail.sysu.edu.cn cst@mail.sysu.edu.cn.
authors.forename: Zhi-Ping
authors.initials: ZP
authors.lastname: Xie
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou, China Shenzhen Research and Development Center of State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Baoan, Shenzhen, China xiezping@mail.sysu.edu.cn cst@mail.sysu.edu.cn.
authors.forename: Christian
authors.initials: C
authors.lastname: Staehelin
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D020935:MAP Kinase Signaling System; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D027805:Phaseolus / Q000502:physiology; D010766:Phosphorylation; D055170:Plant Root Nodulation; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D020579:Sinorhizobium / Q000201:enzymology / Q000378:metabolism*; D013379:Substrate Specificity; D013559:Symbiosis; D014026:Nicotiana
chemical_list: D001426:Bacterial Proteins; D012694:Serine; D020928:Mitogen-Activated Protein Kinases
keywords: Effector; NopL; Sinorhizobium (Ensifer) sp. strain NGR234; mitogen-activated protein kinase; multiple phosphorylation; type 3 protein secretion system.