Loss-of-function of ASPARTIC PEPTIDASE NODULE-INDUCED 1 (APN1) in Lotus japonicus restricts efficient nitrogen-fixing symbiosis with specific Mesorhizobium loti strains

Hiroko Yamaya-Ito, Yoshikazu Shimoda, Tsuneo Hakoyama, Shusei Sato, Takakazu Kaneko, Md Shakhawat Hossain, Satoshi Shibata, Masayoshi Kawaguchi, Makoto Hayashi, Hiroshi Kouchi, Yosuke Umehara

    Research output: Contribution to journalArticlepeer-review

    21 Citations (Scopus)

    Abstract

    The nitrogen-fixing symbiosis of legumes and Rhizobium bacteria is established by complex interactions between the two symbiotic partners. Legume Fix mutants form apparently normal nodules with endosymbiotic rhizobia but fail to induce rhizobial nitrogen fixation. These mutants are useful for identifying the legume genes involved in the interactions essential for symbiotic nitrogen fixation. We describe here a Fix mutant of Lotus japonicus, apn1, which showed a very specific symbiotic phenotype. It formed ineffective nodules when inoculated with the Mesorhizobium loti strain TONO. In these nodules, infected cells disintegrated and successively became necrotic, indicating premature senescence typical of Fix mutants. However, it formed effective nodules when inoculated with the M. loti strain MAFF303099. Among nine different M. loti strains tested, four formed ineffective nodules and five formed effective nodules on apn1 roots. The identified causal gene, ASPARTIC PEPTIDASE NODULE-INDUCED 1 (LjAPN1), encodes a nepenthesin-type aspartic peptidase. The well characterized Arabidopsis aspartic peptidase CDR1 could complement the strain-specific Fix phenotype of apn1. LjAPN1 is a typical late nodulin; its gene expression was exclusively induced during nodule development. LjAPN1 was most abundantly expressed in the infected cells in the nodules. Our findings indicate that LjAPN1 is required for the development and persistence of functional (nitrogen-fixing) symbiosis in a rhizobial strain-dependent manner, and thus determines compatibility between M. loti and L. japonicus at the level of nitrogen fixation.

    Original languageEnglish
    Pages (from-to)5-16
    Number of pages12
    JournalPlant Journal
    Volume93
    Issue number1
    DOIs
    Publication statusPublished - 2018 Jan

    Keywords

    • Lotus japonicus
    • aspartic peptidase
    • late nodulin
    • nodule
    • restriction of symbionts
    • rhizobia–legume symbiosis

    ASJC Scopus subject areas

    • Genetics
    • Plant Science
    • Cell Biology

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