The nodulation programme is regulated systemically in leguminous hosts. This mechanism is referred to as the autoregulation of nodulation. Recently, a gene involved in the regulation has been isolated from the model legume Lotus japonicus (HAR1), soybean (NTS1/GmNARK) and pea (PsSYM29) that encode a receptorlike kinase, similar to the well-characterized Arabidopsis CLAVATA1. Here we report the sequencing and expression analysis of the NTS1/GmNARK gene and its homolog GmCLV1A in a soybean

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... dulating cultivar, Sakukei 4, which shows a high yielding ability, especially in fields with low nitrogen fertility. Sequencing of the NTS1/GmNARK gene showed that Sakukei 4 has a nonsense mutation (AAA to TAA) near the transmembrane domain as well as En6500 that is the paternal donor parent of Sakukei 4. This mutation is involved in the supernodulating phenotype in both lines En6500 and Sakukei 4. There were no mutations in the GmCLV1A gene, including a single intron between the wild-type, Enrei and both supernodulating lines. Transcripts of both genes were detected in rhizobium-inoculated or non-inoculated cotyledons (7 day-old), primary leaves (14 day-old), leaves (21 day-old) and leaves (14 days after inoculation) by non-quantitative RT-PCR analysis. In the nodules and leaf buds, including the shoot apical meristem where CLAVATA1 is expressed in Arabidopsis, both transcripts were also detected. We observed that NTS1/GmNARK and its homolog GmCLV1A are transcribed constitutively in all the organs we examined, regardless of the presence of symbiosis, stage of growth and normal or mutant status. It is concluded that may be necessary for a leguminous host to initiate the autoregulation system immediately after germination.