Nucleotide Sequence and Putative Regulatory Elements of a Nodule-Development-Specific Member of the Soybean (Glycine max) Chalcone Synthase Multigene Family, Gmchs 7

Abstract

Certain plant flavonoids identified in exudates of the roots of leguminous plants are highly effective inducers of nod genes. In soybean (Glycine max L. Merr) the isoflavone daizein has been identified as a naturally occurring inducer of Bradyrhizobium japonicum nod genes (Long, 1989). Estabrook and Sengupta-Gopalan (1991) have demonstrated that a gene encoding CHS, a key enzyme of flavonoid biosynthesis, is specifically induced during nodulation of soybean. They isolated RNA from nodules and sequenced a partial cDNA clone (cEUC2) encoding exon 2 of CHS (Estabrook and SenguptaGopalan, 1991). On the other hand, in the course of characterizing the soybean chs multigene family, we found a family member, gene 7, having a sequence almost identical with that published for exon 2 and the 3' flanking region of cEUC2 (Fig. 1). Thus, we call gene 7 a nodule-developmentspecific member of the soybean chs family. A comparison of the nucleotide sequence of the proteincoding region of gene 7 with those of genes 1, 3, and 4 (Akada et al., 1991, and refs. therein) shows that the former has a substantially lower similarity to the latter three genes, which among themselves have >98% similarity (Table l). It is also interesting to note that the similarity of gene 7 to bean and kudzu vine chs genes (Ryder et al., 1987; Nakajima et al., 1991) is considerably higher than to genes 1, 3, and 4 at both nucleotide and amino acid sequence levels (Table I). Gene 7 has a protein-coding exon 1 of 178 bp, an intron of 445 bp, and an exon 2 of 992 bp, giving rise to an open reading frame of 1170 bp encoding a 389-amino acid polypeptide. The size of the intron is larger than that of genes 1, 3, or 4 by 323 to 324 bp, and the size of exon 2 is larger by 3 bp. Various putative regulatory elements are found in the 5' flanking sequence of gene 7 (Table I). This may imply that the regulation of gene 7 may be quite sophisticated and responsive to a variety of abiotic and biotic stresses. ACKNOWLEDGMENT