NOD FACTORS FROM SINORHIZOBIUM-SAHELI AND SINORHIZOBIUM-TERANGA BV SESBANIAE ARE BOTH ARABINOSYLATED AND FUCOSYLATED, A STRUCTURAL FEATURE SPECIFIC TO SESBANIA-ROSTRATA SYMBIONTS

Sesbania spp, can establish symbiotic interactions with rhizobia from diverse taxonomical origins, including the newly described Sinorhizobi um saheli and S. teranga by. sesbaniae, in addition to the Sesbania ro strata-specific symbiont Azorhizobium caulinodans, These different rhi zobia exhibit a narrow host range, which is limited mainly to Sesbania spp. Nod factors from overproducing strains of S, saheli ORS611 were purified and their structures determined, Remarkably, the terminal red ucing glucosamine of most compounds was found to bear both an arabinos yl group on C-3 and a fucosyl substitution on C-6, Other structural fe atures are as follows: Nod factors are mainly chitopentameric compound s, N-methylated, O-carbamoylated and N-substituted either by a C-18:1 or a C-16:0 acyl chain at their nonreducing end, Nod factors from an o verproducing strain of S, teranga by. sesbaniae ORS604 were found to b e identical to those of S, saheli on the basis of high-pressure liquid chromatography separation and liquid secondary ion mass spectrometry analysis, The Nod factor double glycosylation, i,e,, arabinosylation a nd fucosylation, which appears to be unique to Sesbania symbionts, pro bably reflects a high selection pressure from Sesbania host plants.