CHARACTERIZATION OF A MAJOR MECHANISM FOR THE REGULATION

Huynh, Tu T., Palmitoyl-acyl carrier protein thioesterase in cotton (Gossypium hirsutum L.): biochemical and molecular characterization of a major mechanism for the regulation of palmitic acid content. Doctor of Philosophy (Biochemistry), August 2001, 148 pp., 2 tables, 24 figures, references, 75 titles. The relatively high level of palmitic acid (22 mol%) in cottonseeds may be due in part to the activity of a palmitoyl-acyl carrier protein (ACP) thioesterase (PATE). In embryo extracts, PATE activity was highest at the maximum rate of reserve accumulation (oil and protein). The cotton FatB mRNA transcript abundance also peaked during this developmental stage, paralleling the profiles of PATE enzyme activity and seed oil accumulation. A cotton FatB cDNA clone was isolated by screening a cDNA library with a heterologous Arabidopsis FatB probe (Pirtle et al., 1999, Plant and Cell Physiology 40: 155-163). The predicted amino acid sequence of the cotton PATE preprotein had 63 % identity to the Arabidopsis FatB thioesterase sequence, suggesting that the cotton cDNA clone probably encoded a FatB-type thioesterase. When acyl-CoA synthetase-minus E. coli mutants expressed the cotton cDNA, an increase in 16:0 fre