NODFE-DEPENDENT FATTY-ACIDS THAT LACK AN ALPHA-BETA UNSATURATION ARE SUBJECT TO DIFFERENTIAL TRANSFER, LEADING TO NOVEL PHOSPHOLIPIDS

In Rhizobium leguminosarum, the nodABC and nodFEL operons are involved in the production of lipo-chitin oligosaccharide signals that mediate host specificity, A nodFE-determined, highly unsaturated C18:4 fatty acid (trans-2, trans-4, trans-6, cis-11-octadecatetraenoic acid) is es sential for the ability of the signals to induce nodule meristems and pre-infection thread structures on the host plant Vicia sativa, Of the nod genes, induction of only nodFE is sufficient to modify fatty acid biosynthesis to yield trans-2, trans-4, trans-6, cis-11-octadecatetra enoic acid, with an absorbance maximum of 303 nm, This unusual C18:4 f atty acid is not only found in the lipo-chitin oligosaccharides but is also associated with the phospholipids (O. Geiger, J. E. Thomas-Gates , J. Glushka, H. P. Spaink, and B. J. J. Lugtenberg, 1994, J. Biol, Ch em. 269:11090-11097). Here we report that the phospholipids can contai n other nodFE-derived fatty acids, a C18:3 trans-4, trans-6, cis-11-oc tadecatrienoic acid that has a characteristic absorption maximum at 22 5 nm, and a C18:2 octadecadienoic acid, Neither this C18:3 nor this C1 8:2 fatty acid has to date been observed attached to lipo-chitin oligo saccharides, suggesting that an as yet unknown acyl transferase (presu mably NodA), responsible for the transfer of the fatty acyl chain to t he glycan backbone of the lipo-chitin oligosaccharides, does not trans fer all fatty acids synthesized by the action of NodFE to the lipo-chi tin oligosaccharides, Rather, it must have a preference for alpha-beta unsaturated fatty acids during transfer.