nodZ, a unique host-specific nodulation gene, is involved in the fucosylation of the lipooligosaccharide nodulation signal of Bradyrhizobium japonicum

Abstract

The nodulation genes of rhizobia are regulated by the nodD gene product in response to host-produced flavonoids and appear to encode enzymes involved in the production of a lipo-chitose signal molecule required for infection and nodule formation. We have identified the nodZ gene of Bradyrhizobium japon&um, whose product is required for the addition of a 2-0-methylfucose residue to the terminal reducing N-acetylglucosamine of the nodulation signal. This substitution is essential for the biological activity of this molecule. Mutations in nodZ result in defective nodulation of siratro. Surprisingly, although nodZ clearly codes for nodulation function, it is not regulated by NodD and, indeed, shows elevated expression in planta. Therefore, nodZ represents a unique nodulation gene that is not under the control of NodD and yet is essential for the synthesis of an active nodulation signal.Leguminous plants are infected (nodulated) by the gramnegative, soil bacteria Rhizobium, Azorhizobium, and Bradyrhizobium species, which establish a nitrogen-fixing symbiosis within the roots. There is now considerable information available concerning the genetic traits of these bacteria that are required for the establishment of nitrogen-fixing symbiosis. A number of nodulation (nod, nol) genes have been identified (48). These genes fall into two general groups: the common nod genes (e.g., nodABC) that are essential for nodulation of any host and the host specificity genes that appear to determine specific nodulation of a narrow range of hosts (reviewed in references 13, 14, and 21). Recent evidence indicates that the function of many, if not all, of the nod genes is to synthesize or modify lipooligosaccharide signal molecules that initiate many of the initial nodulation responses in the plant (13, 14, 55). For example, Rhizobium meliloti has been shown to synthesize a sulfated lipooligosaccharide that induces many of the early events of nodulation when applied to alfalfa roots (13,14). Recent results indicate that the protein products of the host specificity genes of R. meliloti, nodHPQ, are involved in the specific sulfation reaction leading to the synthesis of NodRm-1 (e.g., see references 4, 41, and 50). We recently identified the lipooligosaccharide nodulation signals produced by Bradyrhizobium japonicum USDA110 and USDA135 and Bradyrhizobium elkanii USDA61 (9,47 NodD (6,25,33

Structural Requirements of Synthetic and Natural Product Lipo-Chitin Oligosaccharides for Induction of Nodule Primordia on Glycine soja

“…Similar to results previously published on this LCO purified from a B. japonicum nodZ mutant (Stacey et al, 1994), it is inactive in both HAD and NOI assays on G. soja (Table I).…”

Molecular Basis of Symbiotic Promiscuity

“…Since all the usual Glycine max symbionts (B. elkanii, B. japonicum, R. fredii, and strain NGR234) secrete fucosylated Nod factors, the expectation that mutation of nodZ would prevent the nodulation of soybeans was strong. In fact, B. japonicum nodZ is required for nodulation of M. atropurpureum but not of G. max (261). Similarly, nodZ mutants of strain NGR234 produce nonfucosylated Nod factors and are unable to nodulate Pachyrhizus tuberosus but retain the capacity to nodulate soybeans (208).…”

“…Perhaps this suggests that both arabinosylated and fucosylated Nod factors are (nodZ, nolK). Fucose is a frequent substitution, and its addition to Nod factors is encoded by nodZ in many rhizobia (162,171,208,210,261). Since all the usual Glycine max symbionts (B. elkanii, B. japonicum, R. fredii, and strain NGR234) secrete fucosylated Nod factors, the expectation that mutation of nodZ would prevent the nodulation of soybeans was strong.…”

Especificidade hospedeira de variantes Bradyrhizobium spp em soja (cvs peking e clark), caupi e guandu

“…De acordo com Stacey et al (1994), a especificidade hospedeira em B. japonicum estaria relacionada, pelo menos em parte, com a presença do radical 2-Ometilfucose na estrutura básica do oligossacarídeo lipoquitínico (LCO) nesta espécie. Ainda que se tenham informações sobre a influência das substituições no fator Nod, nenhuma correlação exata pode ser feita entre o tipo de LCO produzido pelo rizóbio e a planta que ele nodula (Perret et al, 2000).…”