Search

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 intercellular colonization of the root cortex. The analysis of histochemical GUS staining in transgenic rice plants carrying the Ltp/Gus construct confirm the induction of LTP: gene associated with fungal appressoria formation and penetration area. The induction of Ltp gene expression coincided in time with a transient 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 treatment with SA and Pseudomonas syringae indicating that both genes could be implicated in the plant defence response. The exogenous application of SA to rice interacting with the mycorrhizal fungus did not affect appressoria formation but, instead, resulted in a transient delay of root mycorrhization. Nevertheless, although LTP: maintained a prolonged SA-induced expression level, mycorrhizal formation could still proceed.

The cloning and sequence analysis of a novel gene that encodes a type 2 non-specific lipid transfer-like protein (LTP) from rice is reported. Sequence analysis revealed an ORF encoding a protein showing characteristics of the LTP proteins. However, rice LTP2 is more similar to heterologous LTPs than to rice LTP1, supporting the existence of two distinct families of plant LTPs. Ltp2 mRNA is accumulated only in mature seeds. In vegetative tissues, mRNA was only detected after treatment with abscisic acid (ABA), mannitol or NaCl. Transient expression experiments that the 61 nucleotides upstream of the TATA box, containing two ACGT boxes and the motif I, are sufficient for ABA responsiveness of the Ltp gene.

Several cDNA clones encoding three different lipid transfer proteins (LTPs) have been isolated from rice (Oryza sativa L.) in order to analyse the complexity, the evolution and the expression of the LTP gene family. The mature proteins deduced from three clones exhibited a molecular mass of 9 kDa, in agreement with the molecular mass of other LTPs from plants. The clones were shown to be homologous in the coding region, while the 3' non-coding regions diverged strongly between the clones. The occurrence of at least three small multigene families encoding these proteins in rice was confirmed by Southern blot analysis. When compared with each other and with LTPs from other plants, the cluster including rice LTPs and other cereal LTPs indicated that these genes duplicated rather recently and independently in the different plant phyla. The expression pattern of each gene family was also investigated. Northern blot experiments demonstrated that they are differentially regulated in the different tissues analysed. Components such as salt, salicylic acid and abscisic acid were shown to modulate Ltp gene expression, depending on tissues and gene classes, suggesting a complex regulation of these genes.