Lotus accessions possess multiple checkpoints triggered by different type iii secretion system effectors of the wide-host-range symbiont Bradyrhizobium elkanii USDA61

Shohei Kusakabe, Nahoko Higasitani, Takakazu Kaneko, Michiko Yasuda, Hiroki Miwa, Shin Okazaki, Kazuhiko Saeki, Atsushi Higashitani, Shusei Sato

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)

Abstract

Bradyrhizobium elkanii, a rhizobium with a relatively wide host range, possesses a functional type III secretion system (T3SS) that is involved in symbiotic incompatibility against Rj4-genotype soybean (Glycine max) and some accessions of mung bean (Vigna radiata). To expand our knowledge on the T3SS-mediated partner selection mechanism in the symbiotic legume-rhizobia association, we inoculated three Lotus experimental accessions with wild-type and T3SS-mutant strains of B. elkanii USDA61. Different responses were induced by T3SS in a host genotype-dependent manner. Lotus japonicus Gifu inhibited infection; L. burttii allowed infection, but inhibited nodule maturation at the post-infection stage; and L. burttii and L. japonicus MG-20 both displayed a nodule early senescence-like response. By conducting inoculation tests with mutants of previously reported and newly identified effector protein genes of B. elkanii USDA61, we identified NopF as the effector protein triggering the inhibition of infection, and NopM as the effector protein triggering the nodule early senescence–like response. Consistent with these results, the B. elkanii USDA61 gene for NopF introduced into the Lotus symbiont Mesorhizobium japonicum induced infection inhibition in L. japonicus Gifu, but did not induce any response in L. burttii or L. japonicus MG-20. These results suggest that Lotus accessions possess at least three checkpoints to eliminate unfavorable symbionts, including the post-infection stage, by recognizing different T3SS effector proteins at each checkpoint.

Original languageEnglish
Article numberME19141
JournalMicrobes and environments
Volume35
Issue number1
DOIs
Publication statusPublished - 2020

Keywords

  • Bradyrhizobium elkanii
  • Effector protein
  • Lotus japonicus
  • Partner selection
  • Type III secretion system

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Soil Science
  • Plant Science

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