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The Role of Nod Factor Substituents in Actin Cytoskeleton Rearrangements in Phaseolus vulgaris

¹Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, UNAM. Apartado Postal 510-3, Cuernavaca Morelos 62271, México; ²Department of Mass Spectrometry, Faculty of Chemistry, Utrecht University, Utrecht, The Netherlands; ³Leiden University, Institute of Molecular Plant Sciences, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands; ⁴Biology Department, Morrill Science Center, University of Massachusetts, Box 35810, Amherst 01003-5810, U.S.A.

In order to define the symbiotic role of some of the chemical substituents in the Rhizobium etli Nod factors (NFs), we purified Nod metabolites secreted by the SM25 strain, which carries most of the nodulation genes, and SM17 with an insertion in nodS. These NFs were analyzed for their capabilities to induce root hair curling and cytoskeletal rearrangements. The NFs secreted by strain SM17 lack the carbamoyl and methyl substituents on the nonreducing terminal residue and an acetyl moiety on the fucosyl residue on the reducing-terminal residue as determined by mass spectrometry. We have reported previously that the root hair cell actin cytoskeleton from bean responds with a rapid fragmentation of the actin bundles within 5 min of NF exposure, and also is accompanied by increases in the apical influxes and intracellular calcium levels. In this article, we report that methyl-bearing NFs are more active in inducing root hair curling and actin cytoskeleton rearrangements than nonmethylated NFs. However, the carbamoyl residue on the nonreducing terminal residue and the acetyl group at the fucosyl residue on the reducing terminal residue do not seem to have any effect on root hair curling induction or in actin cytoskeleton rearrangement.

Additional keywords: FITC-phalloidin, lipochitin-oligosaccharide, microinjection.