Regulatory Circuitries of H2O2-Responsive NAC Transcription Factors, JUB1 and STAX in Arabidopsis thaliana

Various environmental stresses such as drought, high salinity, extreme temperatures are known to affect plant growth and productivity, having a great impact on the economy. Leaf senescence is a highly regulated, systematic process, which is basically mediated by developmental age; however it can be influenced by an array of internal and environmental signals. Delayed senescence, accompanied by an extended period of photosynthesis, is often coupled with elevated stress tolerance and/or higher biomass accumulation. Thus, the timing of senescence is crucial in determining crop yield, having great agricultural importance. Both types of senescence, developmental and stress-induced, are mediated by signalling molecules including phytohormones and hydrogen peroxide (H₂O₂), besides others, and involve the action of transcription factors that regulate downstream target genes and together with them establish gene regulatory networks. Our group studies the function of senescence-associated and H₂O₂-responsive transcription factors (TFs) in order to unravel the complex regulatory mechanisms underlying the onset and progression of leaf senescence. Recently, we identified two novel NAC TFs, called JUB1 and STAX, that are induced by H₂O₂ treatment as well as salinity-induced and developmental senescence in Arabidopsis thaliana. Overexpression of both genes leads to delay in flowering, extended leaf longevity and abiotic stress tolerance, whereas their knock-down/knock-out mutants show precocious senescence and lowered abiotic stress tolerance. Our study identified JUB1 to confer abiotic stress tolerance by dampening intracellular H₂O₂ levels. In order to understand the gene regulatory networks controlled by JUB1 and STAX, their binding sites were identified. Using estradiol-induced overexpression in combination with microarray-based transcriptome profiling we were able to identify genes rapidly responding to enhanced JUB1 and STAX expression, representing their candidate direct target genes. Taken together, our data suggest JUB1 and STAX, as key regulators of plant growth as well as abiotic stress responses.