The pea cDNA clone pPsENOD12 represents a gene involved in the infection process during Pisum sativum L.-Rhizobium leguminosarum bv. viciae symbiosis. The ENOD12 protein is composed of pentapeptides containing two hydroxyprolines. The expression of the ENOD12 gene is induced in cells through which the infection thread is migrating, but also in cells that do not yet contain an infection thread. Soluble compounds from Rhizobium are involved in eliciting ENOD12 gene expression. Rhizobium common and host-specific nodulation genes are essential for the production of these compounds. Two ENOD12 genes are expressed in nodules and in stem tissue of uninoculated plants. The gene represented by the cloned ENOD12 mRNA is also expressed in flowers, but a different transcription start may be used.