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Restriction of Host Range by the sym2 Allele of Afghan Pea Is Nonspecific for the Type of Modification at the Reducing Terminus of Nodulation Signals

¹Institute of Molecular Plant Sciences, Clusius Laboratory, Leiden University, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands; ²All-Russia Research Institute for Agricultural Microbiology, Podbelsky shosee 3, 189620 St. Petersburg - Pushkin - 8, Russia; ³Department of Molecular Biology, Agricultural University, Dreijenlaan 3, 6703 HA, Wageningen, The Netherlands

Rhizobium leguminosarum bv. viciae strains producing lipo-chitin oligosaccharides (LCOs) that are O-acetylated at the reducing terminus are required for nodulation of wild pea cultivars originating from Afghanistan that possess the recessive sym2^A allele. The O-acetylation of the reducing sugar of LCOs is mediated by the bacterial nodX gene, which presumably encodes an acetyltransferase. We found that for nodulation on Afghan pea cultivars and sym2^A introgression lines the nodX gene can be functionally replaced by the nodZ gene of Bradyrhizobium japonicum, which encodes a fucosyltransferase that fucosylates the reducing terminus of LCOs. The structure of the nodules, which were induced with normal frequency, was typical for effective pea nodules, and they fixed nitrogen with the same efficiency as nodules induced by nodX-carrying strains.