Research article Functional expression of an acyl carrier protein (ACP) from Azospirillum brasilense alters fatty acid profiles in Escherichia coli and Brassica juncea Jyoti K. Jha a , Saheli Sinha a , Mrinal K. Maiti a, * , Asitava Basu a , Ujjal K. Mukhopadhyay b , Soumitra K. Sen a a IIT-BREF Biotek, Indian Institute of Technology, Kharagpur 721302, India b West Bengal Pollution Control Board, Kolkata 700098, India Received 16 October 2006; accepted 2 March 2007 Available online 12 March 2007 Abstract Acyl carrier protein (ACP) is a central cofactor for de novo fatty acid synthesis, acyl chain modification and chain-length termination during lipid biosynthesis in living organisms. Although the structural and functional organization of the ACPs in bacteria and plant are highly con- served, the individual ACP is engaged in the generation of sets of signature fatty acids required for specific purpose in bacterial cells and plant tissues. Realizing the fact that the bacterial ACP being originated early in molecular evolution is characteristically different from the plant’s counterpart, we explored the property of an ACP from Azospirillum brasilense (Ab), a plant-associative aerobic bacterium, to find its role in changing the fatty acid profile in heterologous systems. Functional expression of Ab-ACP in Escherichia coli, an enteric bacterium, and Brassica juncea, an oil-seed crop plant, altered the fatty acid composition having predominantly 18-carbon acyl pool, reflecting the intrinsic nature of the ACP from A. brasilense which usually has C18:1 rich membrane lipid. In transgenic Brassica the prime increment was found for C18:3 in leaves; and C18:1 and C8:2 in seeds. Interestingly, the seed oil quality of the transgenic Brassica potentially improved for edible purposes, particularly with respect to the enhancement in the ratio of monounsaturated (C18:1)/saturated fatty acids, increment in the ratio of linoleic (C18:2)/linolenic (C18:3) and reduction of erucic acid (C22:1). Ó 2007 Elsevier Masson SAS. All rights reserved. Keywords: Acyl carrier protein; Agrobacterium mediated transformation; Brassica juncea; Azospirillum brasilense; Fatty acid profile; Heterologous expression; Escherichia coli 1. Introduction Acyl carrier protein (ACP) is an essential cofactor of fatty acid synthase (FAS), a multiple enzyme complex for de novo fatty acid synthesis in living organisms. In type-II FAS of plant plastid and bacteria, this small (w9 kDa), soluble and acidic protein carries the growing acyl moiety during various steps of reactions for carbon chain elongation, desaturation and termination; leading to the formation of cell’s required lipid molecules [21,32]. When 4 0 phosphopantetheine (4 0 -PP) prosthetic group is attached to the ACP molecule by holo- ACP synthase (AcpS) at the critical serine residue (generally 36th amino acid of the bacterial mature polypeptide), this is called holo-ACP which is the active form of this protein, whereas the apo-ACP, lacking the prosthetic group, is inactive. During fatty acid biosynthesis, the growing acyl chain is bound to the 4 0 -PP thiol by thioester linkage and the acyl- ACP shuttles amongst the enzymes of FAS and other enzymes Abbreviations: Ab, Azospirillum brasilense; ACP, acyl carrier protein; Ec, Escherichia coli; FAME, fatty acid methyl ester; FAS, fatty acid synthase; GC- FID, gas chromatography-flame ionization detection; TP, transit peptide for chloroplast targeting. * Corresponding author. Tel.: þ91 3222 281084/281086; fax: þ91 3222 277890. E-mail addresses: maitimk@hijli.iitkgp.ernet.in, maitimk@yahoo.co.in (M.K. Maiti). 0981-9428/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.plaphy.2007.03.001 Plant Physiology and Biochemistry 45 (2007) 490e500 www.elsevier.com/locate/plaphy