Down-regulation of an abiotic stress related Nicotiana benthamiana WRKY transcription factor induces physiological abnormalities

Transcription factors (TFs), the DNA binding proteins, play key role in biotic and abiotic stress responses in plants by regulating the expression of downstream target genes. Many different TFs have been cloned and characterized in model plants and a few of them have been shown to have direct role in abiotic stress tolerance. In the present report, we have cloned a partial cDNA of AtWRKY75 like gene (NbWRKY) from the model plant, Nicotiana benthamiana, and studied its expression under whole plant desiccation (drought) stress. To induce drought stress, soil water status (field capacity, FC) was maintained between 60-65% by controlled irrigation and replacing water transpired twice a day. The extent of drought stress was assessed by monitoring the leaf water status and quantifying photosynthetic pigments. The semi-quantitative RT-PCR revealed constitutive expression of NbWRKY and up-regulation under drought. Down-regulation of NbWRKY by virus induced gene silencing (VIGS) produced chlorosis and senescing phenotype in N. benthamiana. The silenced plants showed reduced photosynthesis, efficiency of open PSII reaction centre, and exhibited the symptoms of photoinhibition. The results indicated the indispensable role of NbWRKY in basic physiological processes.