Analysis of ENOD40 expression in alb1 , a symbiotic mutant of Lotus japonicus that forms empty nodules with incompletely
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O R I GI N A L P A P E R
H. Imaizumi-Anraku á H. Kouchi á K. Syono S. Akao á M. Kawaguchi
Analysis of ENOD40 expression in alb1, a symbiotic mutant of Lotus japonicus that forms empty nodules with incompletely developed nodule vascular bundles Received: 22 November 1999 / Accepted: 26 July 2000 / Published online: 5 September 2000 Ó Springer-Verlag 2000
Abstract The alb1 mutant of Lotus japonicus (Ljsym74) forms empty nodules in which most of the bacteria remain in abnormally enlarged infection threads and fail to enter the host plant cells. The alb1 mutant was also found to be defective in dierentiation of rami®ed nodule vascular bundles; only a single vascular bundle dierentiates at the proximal end of the alb1 nodules and it fails to dierentiate further. Histochemical analysis using ¯uorescein-conjugated wheat-germ agglutinin (F-WGA) indicated that the mutation in the ALB1 gene speci®cally aects the dierentiation of vascular bundles in nodules. Analysis of nodulin gene expression revealed that the expression of an early nodulin gene, ENOD40, was very low in alb1 nodules. At early developmental stages of alb1 nodules, the pattern of ENOD40 transcription was essentially the same as that in wild-type
nodules; transcripts were localized in dividing cortical cells and in the pericycle of the root stele opposite nodule primordia, as in wild-type nodules. However, mature alb1 nodules exhibited very weak or no expression of ENOD40 in the peripheral cells of the undeveloped nodule vascular bundle. The ENOD40 expression pattern in alb1 nodules is distinct from that in another ineective mutant, fen1 (Ljsym76), in which ENOD40 expression persists prior to premature senescence. These ®ndings lead us to speculate that ENOD40 may play a role in the dierentiation of nodule vascular bundles. Key words Lotus japonicus á Symbiosis-defective mutant á alb1 á nodule vascular bundle á ENOD40 á Nodule organogenesis
Introduction Communicated by A. Kondorosi H. Imaizumi-Anraku (&) Laboratory of Disease Physiology, Department of Plant Physiology, National Institute of Agrobiological Resources, 2-1-2 Kannondai, Tsukuba, 305-8602 Japan E-mail: [email protected]rc.go.jp Fax: +81-298-388347 H. Imaizumi-Anraku á H. Kouchi á S. Akao Laboratory of Nitrogen Fixation, Department of Plant Physiology, National Institute of Agrobiological Resources, 2-1-2 Kannondai, Tsukuba, 305-8602 Japan H. Imaizumi-Anraku á M. Kawaguchi Department of Life Science, Tokyo University, 3-8-1 Komaba, Meguro-ku, Tokyo, 153-8902 Japan K. Syono Department of Science, Japan Women's University, 2-8-1 Mejirodai, Bunkyo-ku, Tokyo, 112-8681 Japan
Leguminous plants develop nitrogen-®xing root nodules in a symbiosis with rhizobium bacteria. Nodule formation requires the exchange of speci®c signal molecules between the host plants and their microsymbionts, followed by consecutive activation of a unique set of plant genes that are termed nodulin genes. Early nodulin genes, which are activated during very early stages of nodule initiation, have been postulated to play pivo
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