Affiliation:
1. State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen (Zhongshan) University, Guangzhou 510275, China
Abstract
ABSTRACT
Establishment of symbiosis between certain host plants and nitrogen-fixing bacteria (“rhizobia”) depends on type 3 effector proteins secreted via the bacterial type 3 secretion system (T3SS). Here, we report that the open reading frame y4zC of strain NGR234 encodes a novel rhizobial type 3 effector, termed NopT (for nodulation outer protein T). Analysis of secreted proteins from NGR234 and T3SS mutants revealed that NopT is secreted via the T3SS. NopT possessed autoproteolytic activity when expressed in
Escherichia coli
or human HEK 293T cells. The processed NopT exposed a glycine (G50) to the N terminus, which is predicted to be myristoylated in eukaryotic cells. NopT with a point mutation at position C93, H205, or D220 (catalytic triad) showed strongly reduced autoproteolytic activity, indicating that NopT is a functional protease of the YopT-AvrPphB effector family. When transiently expressed in tobacco plants, proteolytically active NopT elicited a rapid hypersensitive reaction.
Arabidopsis
plants transformed with
nopT
showed chlorotic and necrotic symptoms, indicating a cytotoxic effect. Inoculation experiments with mutant derivatives of NGR234 indicated that NopT affected nodulation either positively (
Phaseolus vulgaris
cv. Yudou No. 1;
Tephrosia vogelii
) or negatively (
Crotalaria juncea
). We suggest that NopT-related polymorphism may be involved in evolutionary adaptation of NGR234 to particular host legumes.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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