IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Session Details: Wednesday 30 November 2011
Concurrent Session 11 – Nodule Formation
1100 – 1230
Authors: Christian Staehelin, Ling Zhang, Ying-Ying Ge, Da-Wei Xin, Sha Liao and Zhi-Ping Xie
State Key Laboratory of Biocontrol, School of Life Sciences, SunYat-Sen (Zhongshan)
University, East Campus, Guangzhou 510006, China
Presentation Title: Characterization of type 3 effectors in the Rhizobium-legume symbiosis
Presentation Time: 1120 - 1140
Pathogenic bacteria use type 3 secretion systems to deliver virulence factors (type 3 effector proteins) into
eukaryotic host cells. Similarly, type 3 effectors of certain nitrogen-fixing rhizobial strains affect nodule formation
in the interaction with various host legumes. Here, we characterized NopL and NopM, two type 3 effectors of
Rhizobium sp. strain NGR234. Nodulation tests and microscopic analysis showed that distinct necrotic areas
were rapidly formed in ineffective nodules of Phaseolus vulgaris (cv. Tendergreen) induced by a nopL mutant,
indicating that NopL antagonized nodule senescence. Further experiments revealed that NopL interfered with
mitogen-activated protein kinase (MAPK) signaling in yeast and plant cells (Nicotiana tabacum). Expression of
nopL in yeast disrupted the mating pheromone (α-factor) response pathway, whereas nopL expression in N.
tabacum suppressed cell death induced by over-expression of the MAPK gene SIPK (salicylic acid-induced
protein kinase). NopL was multiply phosphorylated either in yeast or N. tabacum cells that expressed nopL. Four
phosphorylated serines were confirmed by mass spectrometry. All four phosphorylation sites exhibit a Ser-Pro
pattern, a typical motif in MAPK substrates. These data suggest that NopL is a suppressor of MAPK signaling.
NopM, another type 3 effector of Rhizobium sp. NGR234 displayed E3 ubiquitin ligase activity in vitro, whereas
the mutant protein NopM-C338A was inactive. Corresponding mutant analysis indicated that NopM also acts as
an E3 ubiquitin ligase during symbiosis with Lablab purpureus, providing evidence that NopM is delivered into
legume host cells and targets host proteins. Finally, effects of NopM on eukaryotic cells will be reported.
Zhang L, Chen X-J, Lu H-B, Xie Z-P, & Staehelin C (2011). Functional analysis of the type 3 effector NopL from
Rhizobium sp. NGR234: symbiotic effects, phosphorylation and interference with MAPK signaling. J. Biol. Chem.
in press
72
2011