Medicago truncatula ENOD11: A novel RPRP-encoding early nodulin gene expressed during mycorrhization in arbuscule-containing cells

Leguminous plants establish endosymbiotic associations with both rhizobia ( nitrogen fixation) and arbuscular mycorrhizal fungi (phosphate uptake). The se associations involve controlled entry of the soil microsymbiont into the root and the coordinated differentiation of the respective partners to gen erate the appropriate exchange interfaces. As part of a study to evaluate a nalogies at the molecular level between these two plant-microbe interaction s, we focused on genes from Medicago truncatula encoding putative cell wall repetitive proline-rich proteins (RPRPs) expressed during the early stages of root nodulation, Here we report that a novel RPRP-encoding gene, MtENOD 11, is transcribed during preinfection and infection stages of nodulation i n root and nodule tissues. By means of reverse transcription-polymerase cha in reaction and a promoter-reporter gene strategy, we demonstrate that this gene is also expressed during root colonization by endomycorrhizal fungi I n inner cortical cells containing recently formed arbuscules, In contrast, no activation of MtENOD11 is observed during root colonization by a nonsymb iotic, biotrophic Rhizoctonia fungal species. Analysis of transgenic Medica go spp, plants expressing pmtENOD11-gusA also revealed that this gene is tr anscribed in a variety of nonsymbiotic specialized cell types in the root, shoot, and developing seed, either sharing high secretion/metabolite exchan ge activity or subject to regulated modifications in cell shape. The potent ial role of early nodulins with atypical RPRP structures such as ENOD11 and ENOD12 in symbiotic and nonsymbiotic cellular contexts is discussed.