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TOO MUCH LOVE, a Root Regulator Associated with the Long-Distance Control of Nodulation in Lotus japonicus

March 2009 , Volume 22 , Number  3
Pages  259 - 268

Shimpei Magori,1 Erika Oka-Kira,1 Satoshi Shibata,2 Yosuke Umehara,2 Hiroshi Kouchi,2 Yoshihiro Hase,3 Atsushi Tanaka,3 Shusei Sato,4 Satoshi Tabata,4 and Masayoshi Kawaguchi1

1Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033; 2Plant Physiology Department, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan; 3Radiation-Applied Biology Division, Quantum Beam Science Directorate, Japan Atomic Energy Agency, 1233 Watanuki-machi, Takasaki, Gunma 370-1292, Japan; 4Kazusa DNA Research Institute, 2-6-7 Kazusa-kamatari, Kisarazu, Chiba 292-0818, Japan

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Accepted 25 November 2008.

Legume plants tightly control the development and number of symbiotic root nodules. In Lotus japonicus, this regulation requires HAR1 (a CLAVATA1-like receptor kinase) in the shoots, suggesting that a long-distance communication between the shoots and the roots may exist. To better understand its molecular basis, we isolated and characterized a novel hypernodulating mutant of L. japonicus named too much love (tml). Compared with the wild type, tml mutants produced much more nodules which densely covered a wider range of the roots. Reciprocal grafting showed that tml hypernodulation is determined by the root genotype. Moreover, grafting a har1 shoot onto a tml rootstock did not exhibit any obvious additive effects on the nodule number, which was further supported by double mutational analysis. These observations indicate that a shoot factor HAR1 and a root factor TML participate in the same genetic pathway which governs the long-distance signaling of nodule number control. We also showed that the inhibitory effect of TML on nodulation is likely to be local. Therefore, TML may function downstream of HAR1 and the gene product TML might serve as a receptor or mediator of unknown mobile signal molecules that are transported from the shoots to the roots.

© 2009 The American Phytopathological Society