Characterization of cDNA and genomic clones for a palmitoyl-acyl carrier protein thioesterase (FatB1) and an osmotin-like PR5 protein in Gossypium hirsutum

Putative cotton cDNA clones and cognate genomic clones for a palmitoyl-acyl carrier protein (ACP) thioesterase (PATE) and an osmotin-like pathogenesis-related 5 (PR5) protein have been isolated and characterized. PATE is a class B fatty acid thioesterase with specificity for saturated long-chain fatty acids such as palmitate, and is implicated as a key enzyme to be targeted for regulation of fatty acid synthesis in order to alter cotton seed oil profiles. A nearly full-length 1.7-kb cDNA clone was isolated using a hybridization probe derived from an Arabidopsis PATE cDNA clone designated TE 3-2. A 17-kb genomic segment encompassing the PATE gene was also isolated, which has six exons and five introns with high sequence identity with other FatB cDNA/gene sequences. The deduced PATE preprotein amino acid sequence of 413 residues has putative signal sequences for targeting to the chloroplast stroma. PR5 proteins called osmotins are made in response to fungal pathogen stress or osmotic stress (water deprivation or salt exposure). Osmotins may actually form pores in fungal membranes, leading to osmotic rupture and destruction of the fungal cells. A cotton osmotin-like PR5 cDNA insert of 1,052 base-pairs was isolated and shown to encode a preprotein of 242 amino acids and is predicted to be secreted to the extracellular matrix as a neutral isoform. The deduced amino acid sequence has 16 cysteine residues that are highly conserved in osmotin-like proteins and are important in stabilizing the three-dimensional structure seen in thaumatin, zeamatin, and PR5-d. The intronless cognate cotton genomic clone has two putative ethylene response elements (GCC boxes) found in other PR5 gene promoter regions, as well as several tentative promoter/enhancer elements possibly involved in spatial/temporal gene expression.