Involved in the infection process during the plant-rhizobium interaction (Probable). Involved in actinorhizal root nodulation. Involved in symbiotic association with the nitrogen-fixing actinomycete Frankia spp (Probable). Expressed in cotyledons, leaf vasculature, stomatal guard cells and trichomes. In the embryo, expressed in embryo suspensors, the epidermis and underlying tissues of the cotyledons, hypocotyls, and radicle in maturing embryos, and the outer cell layer of the endosperm. Induced during preinfection and infection stages of nodulation in root and nodule tissues. Induced during root colonization by endomycorrhizal fungi in inner cortical cells containing recently formed arbuscules (PubMed:11386369, PubMed:16478046). Induced by Nod factors (PubMed:15489277). Induced during actinorhizal root nodulation following symbiotic association with the nitrogen-fixing actinomycete Frankia spp (PubMed:20459313). Belongs to the plant proline-rich protein superfamily.