Two genes from soybean encoding soluble Δ9 stearoyl-ACP desaturases

The Delta 9 stearoyl acyl-carrier protein desaturase (SACPD) gene of soybean [Glycine max (L.) Merrill] encodes a soluble enzyme that converts stearic to oleic acid. Understanding the regulation of SACPD expression and enzyme activity are thus important steps toward developing soybean lines with altered stearic or oleic acid content. Using primers designed to a G. max SACPD cDNA sequence, a 3648-bp product was cloned and sequenced from the genome of cultivar Dare. Comparison of the third SACPD exon protein sequence with other available Glycine SACPD sequences revealed unique amino acid variability at positions 310 and 313. Sequence-specific primers were designed for Real-time RT-PCR (reverse transcriptase-polymerase chain reaction) for this region of exon 3. Diagnostic and specific products were recovered with these primers using Dare cDNA template and Dare genomic DNA. Sequencing of a second genomic clone from Dare confirmed that there were two SACPD genes, designated A and B, in this cultivar. Survey of the genomes of 51 soybean lines and cultivars with PCR and the gene-specific primers indicated that all 51 had both A and B. Differences between SACPD-A and -B transcript abundance in soybean tissues, while quantifiable, were not dramatic. SACPD-A and -B transcript accumulation for three seed developmental stages between R5 and R6 was essentially equal. Biochemical analysis of the proteins encoded by these two SACPD genes may reveal whether the amino acid variability uncovered in this study has any relation to enzyme activity.