Comparative differential RNA display analysis of arbuscular mycorrhiza in Pisum sativum wild type and a mutant defective in late stage development.

In order to analyse gene expression associated with the late stages of arbuscular mycorrhizal development between Pisum sativum and Glomus mosseae, comparative differential RNA display was carried out using wild-type P. sativum and a mutant, RisNod24, where the fungal partner is not able to form functional arbuscules. Comparison of RNA accumulation patterns between controls, G. mosseae-colonized mutant and wild-type roots resulted in the identification of four differentially occurring cDNA fragments. One of the corresponding genes was from the fungus and three of plant origin. One plant gene, Psam4 (P. sativum arbuscular mycorrhiza-regulated), was analysed in more detail. Sequencing of a cDNA clone showed that Psam4 encodes a proline-rich protein. Northern blot analysis and quantitative RT-PCR revealed a higher basal level of Psam4 RNA accumulation in the mutant compared to the wild type. In both pea genotypes, RNA accumulation was reduced after inoculation with mycorrhiza- or nodule-forming symbiotic microorganisms, but enhanced after infection with a root pathogenic fungus.