Sequence of a Vegetative Homolog of the Pea Seed Lectin Gene

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Legume lectins represent a family of genes that are expressed in seed and vegetative tissues (Vasta and Pont-Lezica, 1990). As genes of a common origin expressed in different phases of the plant life cycle, they represent a model system with which to analyze and understand the divergent evolution of regulatory sequences within higher plants. The PSL RNA accumulates during embryo development (Higgins et al., 1983); its vegetative homolog (Blec) is highly expressed in mersitematic epidermal cells of the pea shoot apex (Dobres and Thompson, 1989; Maiti et al., 1993). Both cDNA sequencing and Southern blot analysis indicate that Blec is a member of a transcribed multigene family (Pak et al., 1992). Restriction fragment length polymorphism analysis indicates that most of these genes are clustered on chromosome 7, close to the PSL gene (N. Weeden, Cornell University, personal communication). The deduced amino acid sequences for four Blec cDNAs were previously reported (Pak et al., 1992). Here we report the sequence of the genomic clone for a member of the Blec gene family (Table I). Comparison of the Blec genomic clone with the four published cDNA sequences for Blecl , Blec2, Blec3, and Blec4 reveals complete identity between Blec4 and the Blec genomic clone, indicating that the Blec genomic clone represents an expressed member of the Blec gene family (Pak et al., 1992). Furthermore, alignment of the coding region for genomic and cDNA clones reveals the absence of any introns. This appears to be a conserved feature of legume lectin genes cloned so far (Harada et al., 1990, and refs. therein). A putative TATA box occurs 64 bp upstream of the ATG initiation codon. A polyadenylation signal and a sequence implicated in correct mRNA 3‘ end formation (McLauchlan et al., 1985) occur at 29 and 74 bp downstream of the TGA translational stop codon. Accordingly, alignment of the 3‘ end of the Blec4 cDNA with the Blec genomic clone shows that polyadenylation occurs at 106 bp downstream of the stop codon. Alignment of the 5’ flanking sequences of Blec and PSL (Gatehouse et al., 1987) reveals extensive sequence divergente between the two genes, except for two short conserved sequence motifs (GGTGTTGTA and TATGTG) 57 and 27 bp upstream of the TATA box in Blec that are present as an uninterrupted 13-bp sequence (GGTGTTGTATATGTG) 17 bp upstream of the TATA box in PSL. Sites identical to the