Sym2 of Pea Is Involved in a Nodulation Factor-Perception Mechanism That Controls the Infection Process in the Epidermis

Abstract

Since the induction of the early nodulin gene FNODl2 in the epidermis and the formation of a nodule primordium in the inner cortex were not affected, we conclude that more than one Nod factor-perception mechanism is active. Furthermore, we show that symp-mediated control of infection-thread growth was affected by the bacterial nodulation gene nodO.Rhizobium bacteria have the ability to induce a developmental process in the root of leguminous plants that results in the formation of a new organ, the root nodule. These new organs create the environment in which the bacteria fix nitrogen to ammonia, which can subsequently be utilized by the plant.The symbiotic interaction of Rhizobium sp. bacteria and leguminous plants is set in motion by the exchange of signal molecules. Plant-excreted flavonoids induce the expression of bacterial nodulation (nod) genes, which are responsible for the synthesis of specific lipochitin oligosaccharides, named Nod factors (Lerouge et al., 1990;Spaink et al., 1991). Nod factors consist of a tetra-or pentameric N-acetylglucosamine backbone with a fatty acyl chain at the nonreducing terminal sugar moiety. Substituents at the terminal sugar residues and the structure of the acyl chain determine the differences in biological activity and host specificity (for review, see Carlson et al., 1994).The role of Nod factor structure in host specificity is exemplified as follows: alfalfa (Medicago sativa) belongs to the cross-inoculation group that can be nodulated by Rhi- zobium meliloti, which produces Nod factors with a sulfate group at the reducing sugar (Lerouge et al., 1990). In contrast, pea (Pisum sativum) is nodulated by Rhizobium leguminosarum bv viciae, which produces Nod factors that lack a substitution at that position (Spaink et al., 1991). When the host-specificity genes nodH, nodP, and nodQ, which are responsible for the sulfation of the Nod factors in R. meliloti, are introduced into R. leguminosarum bv viciae these bacteria can now induce noninfected, nodule-like structures on alfalfa but concomitantly lose their ability to nodulate pea and vetch (Faucher et al

Four Genes of Medicago truncatula Controlling Components of a Nod Factor Transduction Pathway

“…The dissection of Nod factor perception/transduction has so far consisted of pharmacological approaches, identifying potential elements of a Nod factor signal transduction pathway that leads to expression of the early nodulin gene MtENOD12 (Pingret et al, 1998) or the characterization of certain plant mutants. Thus, two genetic loci of pea and one of Lotus japonicus have been studied for their role in Nod factor perception: SYM8 of pea, which is involved in controlling PsENOD5 and PsENOD12A gene expression in response to Nod factors (Albrecht et al, 1998); SYM2 A of pea, which is involved in the specific recognition of Nod factors leading to infection but does not control Nod factor-induced root hair deformation or PsENOD12 expression (Geurts et al, 1997); and NIN of L. japonicus, which does not control the perception of Nod factors that leads to root hair curling and deformation (Schauser et al, 1999). In addition, an alfalfa Nod Ϫ mutant has been characterized that is deficient for calcium spiking in response to Nod factors, suggesting that this mutant is blocked in an early stage of Nod factor signal transduction (Ehrhardt et al, 1996).…”

A model for the development of the rhizobial and arbuscular mycorrhizal symbioses in legumes and its use to understand the roles of ethylene in the establishment of these two symbioses

“…Recently, Genre and Bonfante (2002) proposed that LjSym4 is critical in establishing the proper rearrangement of the Csk in the epidermis; its correct expression would allow the AM fungus to cross the epidermal layer without any obstruction. Thus, we can conclude with certainty that the epidermis, especially at its interface with the cortex, is a strong checkpoint in AM colonization (Geurts et al 1997;Bonfante et al 2000;Senoo et al 2000;Resendes et al 2001). …”

Bridging Model and Crop Legumes through Comparative Genomics

“…Pea SYM2 is a putative Nodfactor entry receptor involved in the rhizobial infection process (Geurts et al, 1997). Map-based cloning of SYM2 in pea was difficult due to its large genome and the lack of efficient transformation methods.…”