Plant and Cell Physiology Advance Access published online on July 2, 2006
Plant and Cell Physiology, doi:10.1093/pcp/pcj081
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1 National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan
* To whom correspondence should be addressed. ENOD40 is one of the most intriguing early nodulin genes that is known to be induced most early in response to interaction of legume plants with symbiotic Rhizobium bacteria, but its function in the nodulation process is still not solved. Lotus japonicus has two ENOD40 genes: LjENOD40-1 is abundantly induced in very early stages of bacterial infection or Nod factor application, whereas LjENOD40-2 is abundantly expressed only in mature nodules. We generated transgenic lines of L. japonicus with an RNAi (RNA interference) construct that expresses hairpin double-stranded RNA for LjENOD40-1 to induce sequence-specific RNA silencing. In the transgenic plants, expression of both LjENOD40-1 and -2 was significantly reduced, and no accumulation of ENOD40 transcripts was detected upon Mesorhizobium loti inoculation. The transgenic plants exhibited very poor nodulation (only 0-2 nodules per plant) and could not grow well without additional nitrogen supply. Analysis of segregation in the T2 progeny indicated that the suppression of nodulation is perfectly linked with the presence of the transgene. Microscopic observation of the infection process using lacZ-labelled Mesorhizobium loti, together with expression analysis of infection-related nodulin genes, demonstrated that ENOD40 knockdown did not inhibit the initiation of bacterial infection process. In contrast, nodule primordium initiation and subsequent nodule development were significantly suppressed in the transgenic plants. These results clearly indicate that ENOD40 is required for nodule initiation and subsequent organogenesis, but not involved in early infection events.
Received May 28, 2006
Accepted June 23, 2006
Regular Paper
RNAi knockdown of ENOD40s leads to significant suppression of nodule formation in Lotus japonicus
Hirotaka Kumagai 1,
Eri Kinoshita 2,
Robert W. Ridge 2,
and
Hiroshi Kouchi 1 *
2 International Christian University, 3-10-2, Osawa, Mitaka, Tokyo 181-8585, Japan
Hiroshi Kouchi, E-mail: kouchih{at}nias.affrc.go.jp
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