Induction of Ltp (lipid transfer protein) and Pal (phenylalanine ammonia-lyase) gene expression in rice roots colonized by the arbuscular mycorrhizalfungus Glomus mosseae

The expression of a lipid transfer protein (LTP) gene is regulated in Oryza sativa roots in response to colonization by the mycorrhizal fungus Glomus mosseae. Transcript levels increased when the fungus forms appressoria and penetrates the root epidermis and decreased at the onset of the intercellul ar colonization of the root cortex. The analysis of histochemical GUS stain ing in transgenic rice plants carrying the Ltp/Gus construct confirm the in duction of Ltp gene associated with fungal appressoria formation and penetr ation area. The induction of Ltp gene expression coincided in time with a t ransient increase in the expression of a phenylalanine ammonia-lyase (Pal) gene and a transient accumulation of salicylic acid (SA) in the mycorrhizal roots. The expression of Ltp and Pal was induced in rice roots after treat ment with SA and Pseudomonas syringae indicating that both genes could be i mplicated in the plant defence response. The exogenous application of SA to rice interacting with the mycorrhizal fungus did not affect appressoria fo rmation but, instead, resulted in a transient delay of root mycorrhization. Nevertheless, although Ltp maintained a prolonged SA-induced expression le vel, mycorrhizal formation could still proceed.