Acyl-lipid thioesterase1-4 from Arabidopsis thaliana form a novel family of fatty acyl-acyl carrier protein thioesterases with divergent expression patterns and substrate specificities.
Hydrolysis of fatty acyl thioester bonds by thioesterases to produce free fatty acids is important for dictating the diversity of lipid metabolites produced in plants. We have characterized a four-member family of fatty acyl thioesterases from Arabidopsis thaliana, which we have called acyl-lipid thioesterase1 (ALT1), ALT2, ALT3, and ALT4. The ALTs belong to the Hotdog fold superfamily of thioesterases. ALT-like genes are present in diverse plant taxa, including dicots, monocots, lycophytes, and microalgae. The four Arabidopsis ALT genes were found to have distinct gene expression profiles with respect to each other. ALT1 was expressed specifically in stem epidermal cells and flower petals. ALT2 was expressed specifically in root endodermal and peridermal cells as well as in stem lateral organ boundary cells. ALT3 was ubiquitously expressed in aerial and root tissues and at much higher levels than the other ALTs. ALT4 expression was restricted to anthers. All four proteins were localized in plastids via an N-terminal targeting sequence of about 48 amino acids. When expressed in Escherichia coli, the ALT proteins used endogenous fatty acyl-acyl carrier protein substrates to generate fatty acids that varied in chain length (C6-C18), degree of saturation (saturated and monounsaturated), and oxidation state (fully reduced and β-ketofatty acids). Despite their high amino acid sequence identities, each enzyme produced a different profile of lipids in E. coli. The biological roles of these proteins are unknown, but they potentially generate volatile lipid metabolites that have previously not been reported in Arabidopsis.
Department of Biology, Institute of Biochemistry, Carleton University, Ottawa, ON, K1S 5B6, Canada.
Ian P
IP
Pulsifer
Christine
C
Lowe
Swara A
SA
Narayaran
Alia S
AS
Busuttil
Sollapura J
SJ
Vishwanath
Frédéric
F
Domergue
Owen
O
Rowland
D000213:Acyl Carrier Protein / Q000378:metabolism; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D017403:In Situ Hybridization; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D030821:Plants, Genetically Modified; D018087:Plastids / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013869:Thiolester Hydrolases / Q000235:genetics* / Q000378:metabolism; D059467:Transcriptome
D000213:Acyl Carrier Protein; D029681:Arabidopsis Proteins; D005227:Fatty Acids; D007527:Isoenzymes; D049452:Green Fluorescent Proteins; D013869:Thiolester Hydrolases; C018748:oleoyl-(acyl-carrier-protein) hydrolase