Abstract
WRKY transcription factors play an important role in transcriptional reprogramming associated with plant abiotic stress responses. In this study, the role of Solanum tuberosum (S. tuberosum; St) WRKY transcription factors StWRKY4 and StWRKY56 were explored in response to salt stress by generating transgenic potato lines using RNAi. The results showed that the total chlorophyll content in transgenic StWRKY4 was 6.1 mg/g at 200 mM after 35 days; however, in StWRKY56, an elevated 12.6 mg/g total chlorophyll was observed which indicated different operating mechanisms of these StWRKY transcription factors under salt stress. Proline content increased to 1.0 mg/g in StWRKY4 while it decreased to 0.54 mg/g in StWRKY56 as compared to their respective control plants after 35 days at 200 mM of salt stress. For Na(+)/K(+) ratios, StWRKY4 and StWRKY56 showed 32.3 and 5.5 values, respectively, in silenced plants under similar conditions. This shows contrasting trends in StWRKY4 and StWRKY56 for Na(+)/K(+). However, the expression analyses of StSOS1s were found to be upregulated, whereas for StNHX3s these were found to be downregulated in StWRKY4 and StWRKY56 under salt stress. Thus, this study, for the first time, demonstrated the different but critical roles of StWRKY4 and StWRKY56 for fine-regulating salt stress tolerance in complex signaling network of potato plant.