Abstract
AbstractRNA‐dependent RNA polymerase (RDR‐1) is known to be induced by salicylic acid and is involved in basal resistance in plants against pathogen infection. Transgenic lines of tobacco plant (Nicotiana tabacum cv. Samsun NN) variably silenced for RDR‐1 gene were assayed for peroxidase (POX) activity following a systemic infection with Potato virus Y strain O (PVYo). Guaiacol‐POX specific activity increased more than twofold in un‐inoculated upper leaves of susceptible tobacco lines silenced for RDR‐1, 30 days after inoculation with PVYo relative to the wild type. The number and intensity of POX isozymes in intercellular fluid of leaves showing systemic symptoms varied among the transgenic lines. Transgenic line R‐5‐1 susceptible to PVYo infection with much lower accumulation of RDR‐1 transcript showed two new POX activity bands compared to R‐14‐1 line that is moderately suppressed for RDR‐1. Using semi‐quantitative RT‐PCR, RDR‐1, MYB1 (transcription factor) and PVYo RNA accumulation levels were assessed. Transgenic lines with a greater degree of susceptibility to the virus infection exhibited lower levels of transcript accumulation for both RDR‐1 and MYB1 genes. These results suggest that down‐regulation of RDR‐1 transcript can lead to an alteration in expression pattern of defence‐related genes such as POX and MYB1 and enhanced accumulation of PVYo in tobacco plants.
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