Fig. 5. Isolation of the FON1 gene and characteristics of the FON1 protein. (A) Positional cloning of FON1. (B) Schematic representation of FON1 and CLV1. The LRR and Ser/Thr kinase domains are shown by rectangles, and the amino acid identities of these two domains are indicated. Closed triangles indicate the mutation sites of fon1-1 and fon1-2; open triangle shows the position of the intron. SP, signal peptide; TM, transmembrane domain. (C) Amino acid alignment of the LRR domain and its flanking sequence, with conserved cysteine residues indicated (asterisks). Amino acid numbers: FON1 54-628, CLV1 54-623. Sequences of the cDNA and genomic DNA of FON1 are deposited in DDBJ under accession numbers AB182388 and AB182389, respectively. (D) Amino acid alignment of the Ser/Thr kinase domain. Amino acid numbers: FON1 684-977, CLV1 672-967. Open triangle shows the position of the intron. (E) Phylogenic tree of LRR-type receptor kinases similar to FON1 and CLV1. Amino acids of the kinase domain (D) were compared and the tree was constructed by neighbor-joining methods (Saitou and Nei, 1987) using At4g20270 as a root. Numbers indicate bootstrap values. The intron positions of uncharacterized rice (FON1-like1, AC099732; FON1-like2, AC092781) and Arabidopsis (At4g20270, At3g49670, At5g65700) genes were deduced by comparing amino acid sequences and by the GT-AG rule for spliceosomal introns. Except for OsLRK1 (rice), the other known proteins are legume proteins, including those responsible for hypernodulation (HAR1, SYM29, NTS1).