AUTHOR=Xiang Qi-Wang , Bai Juan , Cai Jie , Huang Qin-Ying , Wang Yan , Liang Ying , Zhong Zhi , Wagner Christian , Xie Zhi-Ping , Staehelin Christian 

TITLE=NopD of Bradyrhizobium sp. XS1150 Possesses SUMO Protease Activity

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00386

DOI=10.3389/fmicb.2020.00386

ISSN=1664-302X

ABSTRACT=<p>Effectors secreted by the type III protein secretion system (T3SS) of rhizobia are host-specific determinants of the nodule symbiosis. Here, we have characterized NopD, a putative type III effector of <italic>Bradyrhizobium</italic> sp. XS1150. NopD was found to possess a functional N-terminal secretion signal sequence that could replace that of the NopL effector secreted by <italic>Sinorhizobium</italic> sp. NGR234. Recombinant NopD and the C-terminal domain of NopD alone can process small ubiquitin-related modifier (SUMO) proteins and cleave SUMO-conjugated proteins. Activity was abolished in a NopD variant with a cysteine-to-alanine substitution in the catalytic core (NopD-C<sub>972</sub>A). NopD recognizes specific plant SUMO proteins (AtSUMO1 and AtSUMO2 of <italic>Arabidopsis thaliana</italic>; GmSUMO of <italic>Glycine max</italic>; PvSUMO of <italic>Phaseolus vulgaris</italic>). Subcellular localization analysis with <italic>A. thaliana</italic> protoplasts showed that NopD accumulates in nuclear bodies. NopD, but not NopD-C<sub>972</sub>A, induces cell death when expressed in <italic>Nicotiana tabacum</italic>. Likewise, inoculation tests with constructed mutant strains of XS1150 indicated that nodulation of <italic>Tephrosia vogelii</italic> is negatively affected by the protease activity of NopD. In conclusion, our findings show that NopD is a symbiosis-related protein that can process specific SUMO proteins and desumoylate SUMO-conjugated proteins.</p>