Identification and characterization of barley RNA-directed RNA polymerases.

RNA-directed RNA polymerases (RDRs) play crucial roles in the RNA silencing response of plants by enhancing and maintaining silencing signals. At least two members of the RDR group, namely RDR1 and RDR6, are implicated in defence against plant viruses. RDRs have so far only been characterized in dicot species. In this report, we identified and characterized HvRDR1, HvRDR2 and HvRDR6 genes in the monocot plant barley (Hordeum vulgare). We analysed their expression under various biotic and abiotic stresses including fungal and viral infections, salicylic acid treatment as well as during plant development. The different classes and subclasses of barley RDRs displayed contrasting expression patterns during pathogen challenge and development suggesting their involvement in specific regulatory pathways. Their response to heat and salicylic acid treatment suggests a conserved pattern of expression of these genes between monocot and dicot plant species. The existence of two HvRDR1 and two HvRDR6 genes suggests an evolutionary selection for specialization in response to biotic and abiotic stresses after gene duplication.