The integral membrane protein SEN1 is required for symbiotic nitrogen fixation in lotus japonicus nodules

Tsuneo Hakoyama, Kaori Niimi, Takeshi Yamamoto, Sawa Isobe, Shusei Sato, Yasukazu Nakamura, Satoshi Tabata, Hirotaka Kumagai, Yosuke Umehara, Katja Brossuleit, Thomas R. Petersen, Niels Sandal, Jens Stougaard, Michael K. Udvardi, Masanori Tamaoki, Masayoshi Kawaguchi, Hiroshi Kouchi, Norio Suganuma

Research output: Contribution to journalArticlepeer-review

76 Citations (Scopus)


Legume plants establish a symbiotic association with bacteria called rhizobia, resulting in the formation of nitrogen-fixing root nodules. A Lotus japonicus symbiotic mutant, sen1, forms nodules that are infected by rhizobia but that do not fix nitrogen. Here, we report molecular identification of the causal gene, SEN1, by map-based cloning. The SEN1 gene encodes an integral membrane protein homologous to Glycine max nodulin-21, and also to CCC1, a vacuolar iron/manganese transporter of Saccharomyces cerevisiae, and VIT1, a vacuolar iron transporter of Arabidopsis thaliana. Expression of the SEN1 gene was detected exclusively in nodule-infected cells and increased during nodule development. Nif gene expression as well as the presence of nitrogenase proteins was detected in rhizobia from sen1 nodules, although the levels of expression were low compared with those from wild-type nodules. Microscopic observations revealed that symbiosome and/or bacteroid differentiation are impaired in the sen1 nodules even at a very early stage of nodule development. Phylogenetic analysis indicated that SEN1 belongs to a protein clade specific to legumes. These results indicate that SEN1 is essential for nitrogen fixation activity and symbiosome/bacteroid differentiation in legume nodules.

Original languageEnglish
Pages (from-to)225-236
Number of pages12
JournalPlant and Cell Physiology
Issue number1
Publication statusPublished - 2012 Jan


  • Bacteroid differentiation
  • Legume-Rhizobium symbiosis
  • Lotus japonicus
  • Nitrogen fixation
  • Nodule
  • Symbiosome


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