The regulation of the SARK promoter activity by hormones and environmental signals

The Senescence Associated Receptor Protein Kinase (PSARK) promoter, fused to isopentenyltransferase (IPT) gene has been shown to promote drought tolerance in crops. We dissected PSARK in order to understand the various elements associated with its activation and suppression. The activity of PSARK was higher in mature and early senescing leaves, and abiotic stress induced its activity in mature leaves. Bioinformatics analysis suggests the interactions of multiple cis-acting elements in the control of PSARK activity. In vitro gel shift assays and yeast one hybrid system revealed interactions of PSARK with transcription factors related to abscisic acid and cytokinin response. Deletion analysis of PSARK, fused to GUS-reporter gene was used to identify specific regions regulating transcription under senescence or during drought stress. Effects of exogenous hormonal treatments were characterized in entire plants and in leaf disk assays, and regions responsive to various hormones were defined. Our results indicate a complex interaction of plant hormones and additional factors modulating PSARK activity under stress resulting in a transient induction of expression.

► Functional cis-elements that could be involved in the regulation of SARK activation were identified.
► The presence of MYB1AT elements supports possible roles in signaling via ABA.
► Specific regions of SARK are associated with the response to cytokinins.
► All the cis-elements positioned along the entire promoter are required for full activity.
► The cis-element response to different hormones enable cross-talk between signaling pathways.