A Positive Regulator of Nodule Organogenesis, NODULE INCEPTION, Acts as a Negative Regulator of Rhizobial Infection in Lotus japonicus.
Legume-rhizobium symbiosis occurs in specialized root organs called nodules. To establish the symbiosis, two major genetically controlled events, rhizobial infection and organogenesis, must occur. For a successful symbiosis, it is essential that the two phenomena proceed simultaneously in different root tissues. Although several symbiotic genes have been identified during genetic screenings of nonsymbiotic mutants, most of the mutants harbor defects in both infection and organogenesis pathways, leading to experimental difficulty in investigating the molecular genetic relationships between the pathways. In this study, we isolated a novel nonnodulation mutant, daphne, in Lotus japonicus that shows complete loss of nodulation but a dramatically increased numbers of infection threads. Characterization of the locus responsible for these phenotypes revealed a chromosomal translocation upstream of NODULE INCEPTION (NIN) in daphne. Genetic analysis using a known nin mutant revealed that daphne is a novel nin mutant allele. Although the daphne mutant showed reduced induction of NIN after rhizobial infection, the spatial expression pattern of NIN in epidermal cells was broader than that in the wild type. Overexpression of NIN strongly suppressed hyperinfection in daphne, and daphne phenotypes were partially rescued by cortical expression of NIN. These observations suggested that the daphne mutation enhanced the role of NIN in the infection pathway due to a specific loss of the role of NIN in nodule organogenesis. Based on these results, we provide evidence that the bifunctional transcription factor NIN negatively regulates infection but positively regulates nodule organogenesis during the course of the symbiosis.
Division of Symbiotic Systems, National Institute for Basic Biology, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Basic Biology, School of Life Science, Graduate University for Advanced Studies, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Biology, Graduate School of Science, Kobe University, Kobe 657-8501, Japan (K.T., H.F.); andResearch Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan (H.M.).
Emiko
E
Yoro
Division of Symbiotic Systems, National Institute for Basic Biology, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Basic Biology, School of Life Science, Graduate University for Advanced Studies, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Biology, Graduate School of Science, Kobe University, Kobe 657-8501, Japan (K.T., H.F.); andResearch Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan (H.M.).
Takuya
T
Suzaki
Division of Symbiotic Systems, National Institute for Basic Biology, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Basic Biology, School of Life Science, Graduate University for Advanced Studies, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Biology, Graduate School of Science, Kobe University, Kobe 657-8501, Japan (K.T., H.F.); andResearch Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan (H.M.).
Koichi
K
Toyokura
Division of Symbiotic Systems, National Institute for Basic Biology, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Basic Biology, School of Life Science, Graduate University for Advanced Studies, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Biology, Graduate School of Science, Kobe University, Kobe 657-8501, Japan (K.T., H.F.); andResearch Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan (H.M.).
Hikota
H
Miyazawa
Division of Symbiotic Systems, National Institute for Basic Biology, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Basic Biology, School of Life Science, Graduate University for Advanced Studies, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Biology, Graduate School of Science, Kobe University, Kobe 657-8501, Japan (K.T., H.F.); andResearch Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan (H.M.).
Hidehiro
H
Fukaki
Division of Symbiotic Systems, National Institute for Basic Biology, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Basic Biology, School of Life Science, Graduate University for Advanced Studies, Okazaki, Aichi 444-8585, Japan (E.Y., T.S., M.K.);Department of Biology, Graduate School of Science, Kobe University, Kobe 657-8501, Japan (K.T., H.F.); andResearch Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan (H.M.) masayosi@nibb.ac.jp.
Masayoshi
M
Kawaguchi