The NopD effector of Bradyrhizobium XS1150 is phosphorylated by mitogen-activated protein kinases and promotes soybean nodulation.

NopD from Bradyrhizobium sp. XS1150 is phosphorylated by MAPKs and, with intact TR phosphorylation sites, enhances soybean nodulation.

• Why it matters: Rhizobial T3SS effectors are key, host-specific determinants of nodule symbiosis, but how NopD is regulated by plant signaling and which residues control activity was unclear.
• What they did: Using a NopD-calmodulin-dependent adenylate cyclase fusion in Sinorhizobium sp. NGR234, the study showed NopD translocation into Vigna unguiculata nodule cells, identified four MAPK phosphorylation sites in NopD’s TR domain, and tested NopD variants in Arabidopsis protoplasts and tobacco cells.
• The result: In soybean, an XS1150 nopD mutant induced fewer nodules than wild type, and in soybean and bean nodules only NopD (not NopD4A or NopDΔTR) suppressed premature senescence and enhanced nodulation, establishing phosphorylation-site-dependent effector activity.