Plant Genome IV Conference Plant Genome IV Conference
Lignin is associated with nutritive value in alfalfa (Medicago sativa L.). Lignification reduces forage digestibility and limits animal performance. Lignin is an aromatic secondary metabolite. Aromatic amino acids are synthesized via the shikimate pathway, in which 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase (EC 4.1.2.15) is the first regulatory enzyme. A cDNA encoding DAHP synthase (designated MsDHS1) was isolated from alfalfa RNA by reverse transcription and polymerase chain reaction using degenerate primers for the conserved regions of known DAHP synthase sequences from other species. DNA fragments of about 875 bp were subcloned into EcoR I-cleaved pCR II, and sequenced. The MsDHS1 sequence consists of an open reading frame of 291 codons with 46.4% of (C+G) content and 80.8C ds DNA melting temperature. The sequence of the deduced 291 amino acids of MsDHS1 was compared with those of two Arabidopsis thaliana (AtDHS1, AtDHS2), two tomato (LeDHS1, LeDHS2), two potato (StshKA, StshKB), and one tobacco (NtDAHPS-1) genes. The results show sequence similarities of 88.7%, 88.0%, 87.3%, and 87.0% to AtDHS2, LeDHS2, NtDAHPS-1, and StshKA, respectively, and relatively lower similarities of 83.9%, 85.9%, and 85.6% to AtDHS1, LeDHS1, and StshKB, respectively, suggesting that MsDHS1 is highly conserved. The predicted molecular weight of the polypeptide encoded by MsDHS1 is 32,456.9.