1. Department of Life Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku, Tokyo 163-8902, Japan
2. Faculty of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba 271-8510, Japan
3. National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan
4. Department of Environmental Sciences, Faculty of Science, Niigata University, Ikarashi, Niigata City 950-2181, Japan
5. Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Corporation, 4-1-8 Honcho, Kawaguchi City, Saitama 332-0012, Japan
6. These authors contributed equally to this work
7. Present address: Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720-3206, USA

Correspondence to: Masayoshi Kawaguchi^6,7 Correspondence and requests for materials should be addressed to M.K. (e-mail: Email: masayosi@env.sc.niigata-u.ac.jp). The sequences for BAC259.12D-1, BAC259.12D-2, L. japonicus HAR1 gene, and soybean NTS1 gene have been deposited in the DDBJ database under accession numbers AB092808, AB092809, AB092810 and AB092811, respectively.

Abstract

Symbiotic root nodules are beneficial to leguminous host plants; however, excessive nodulation damages the host because it interferes with the distribution of nutrients in the plant. To keep a steady balance, the nodulation programme is regulated systemically in leguminous hosts^{1, 2}. Leguminous mutants that have lost this ability display a hypernodulating phenotype. Through the use of reciprocal and self-grafting studies using Lotus japonicus hypernodulating mutants, har1 (also known as sym78)³, we show that the shoot genotype is responsible for the negative regulation of nodule development. A map-based cloning strategy revealed that HAR1 encodes a protein with a relative molecular mass of 108,000, which contains 21 leucine-rich repeats, a single transmembrane domain and serine/threonine kinase domains. The har1 mutant phenotype was rescued by transfection of the HAR1 gene. In a comparison of Arabidopsis receptor-like kinases, HAR1 showed the highest level of similarity with CLAVATA1 (CLV1)⁴. CLV1 negatively regulates formation of the shoot and floral meristems through cell–cell communication involving the CLV3 peptide⁵. Identification of hypernodulation genes thus indicates that genes in leguminous plants bearing a close resemblance to CLV1 regulate nodule development systemically, by means of organ–organ communication.

1. Department of Life Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku, Tokyo 163-8902, Japan
2. Faculty of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba 271-8510, Japan
3. National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan
4. Department of Environmental Sciences, Faculty of Science, Niigata University, Ikarashi, Niigata City 950-2181, Japan
5. Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Corporation, 4-1-8 Honcho, Kawaguchi City, Saitama 332-0012, Japan
6. These authors contributed equally to this work
7. Present address: Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720-3206, USA

Correspondence to: Masayoshi Kawaguchi^6,7 Correspondence and requests for materials should be addressed to M.K. (e-mail: Email: masayosi@env.sc.niigata-u.ac.jp). The sequences for BAC259.12D-1, BAC259.12D-2, L. japonicus HAR1 gene, and soybean NTS1 gene have been deposited in the DDBJ database under accession numbers AB092808, AB092809, AB092810 and AB092811, respectively.