This paper shows that lipo-oligosaccharides (Nod factors) synthesized by Rhizobium bacteria elicit the induction of infection-related early nodulin genes (PsENOD5 and PsENOD12) in pea root hairs. R. leguminosarum bv. viciae secretes a mixture of Nod factors containing a C18 fatty acid chain with 4 (C18:4) or 1 double bond (C18:1). Purified Nod factors harbouring either a C18:4 or a C18:1 acyl moiety induce the expression of the pea early nodulin genes, PsENOD5 and PsENOD12, but the kinetics of induction are different. The expression of both early nodulin genes is induced in a transient manner by the purified Nod factors while a mixture of the Nod factors extends the period during which these genes are expressed. In spite of the host-specific nature of the infection process, heterologous Nod factors of R. meliloti also induce the expression of PsENOD5 and PsENOD12 genes, though with a marked delay compared with the homologous compounds.
A full-length cDNA, PPRG2, representing a gene highly expressed in dodder (Cuscuta trifolii Bab et. Gibs)-infected alfalfa (Medicago sativa L.) stems was isolated by differential screening. The predicted protein contains 157 amino acids and belongs to the PR-10 family of the pathogenesis-related genes with putative ribonuclease activities. Northern hybridizations showed that PPRG2 is transcribed in root and crops of uninfected alfalfa and is induced not only by dodder attack but also by bacterial infections and a large variety of environmental stresses.
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