Arabidopsis thaliana WRKY25 Transcription Factor Mediates Oxidative Stress Tolerance and Regulates Senescence in a Redox-Dependent Manner

Abstract

Senescence is the last developmental step in plant life and is accompanied by a massive change in gene expression implying a strong participation of transcriptional regulators. In the past decade, the WRKY53 transcription factor was disclosed to be a central node of a complex regulatory network of leaf senescence and to underlie a tight multi-layer control of expression, activity and protein stability. Here, we identify WRKY25 as a redoxsensitive upstream regulatory factor of WRKY53 expression. Under non-oxidizing conditions, WRKY25 binds to a specific W-box in the WRKY53 promoter and acts as a positive regulator of WRKY53 expression in a transient expression system using Arabidopsis protoplasts, whereas oxidizing conditions dampened the action of WRKY25. However, overexpression of WRKY25 did not accelerate senescence but increased lifespan of Arabidopsis plants, whereas the knockout of the gene resulted in the opposite phenotype, indicating a more complex regulatory function of WRKY25 within the WRKY subnetwork of senescence regulation. In addition, overexpression of WRKY25 mediated higher tolerance to oxidative stress and the intracellular H 2 O 2 level is lower in WRKY25 overexpressing plants and higher in wrky25 mutants compared to wildtype plants suggesting that WRKY25 is also involved in controlling intracellular redox conditions. Consistently, WRKY25 overexpressers had higher and wrky mutants lower H 2 O 2 scavenging capacity. Like already shown for WRKY53, MEKK1 positively influenced the activation potential of WRKY25 on the WRKY53 promoter. Taken together, WRKY53, WRKY25, MEKK1 and H 2 O 2 interplay with each other in a complex network. As H 2 O 2 signaling molecule participates in many stress responses, WRKK25 acts most likely as integrators of environmental signals into senescence regulation.

Arabidopsis WRKY53, a Node of Multi-Layer Regulation in the Network of Senescence

“…However, not all WRKYs appear to act redox-sensitive: WRKY18 does not show any functional changes under different redox-conditions [82] whereas WRKY70 binding to the W-box 2 of the WRKY53 promoter is more efficient under oxidizing conditions (unpublished results). WRKY53 itself is also redox-sensitive but only to a low extent [82]; however, in protoplasts of wrky53 mutant cells activation of WRKY53 promoter-driven reporter gene expression is almost completely abolished, indicating that the WRKY53 protein itself plays a role in the H 2 O 2 response of its own gene [72]. Furthermore, REV is also involved in the activation of WRKY53 transcription by ROS as in the rev mutants the induction is dampened in a concentration-dependent manner.…”

“…Here again, a feedback control is installed. Overexpression of WRKY25 in transgenic Arabidopsis plants mediated higher tolerance to oxidative stress and the intracellular H 2 O 2 level is lower in these plants but higher in wrky25 mutants compared to wildtype plants, suggesting that WRKY25 itself is involved in controlling intracellular redox conditions [82]. However, not all WRKYs appear to act redox-sensitive: WRKY18 does not show any functional changes under different redox-conditions [82] whereas WRKY70 binding to the W-box 2 of the WRKY53 promoter is more efficient under oxidizing conditions (unpublished results).…”

“…Overexpression of WRKY25 in transgenic Arabidopsis plants mediated higher tolerance to oxidative stress and the intracellular H 2 O 2 level is lower in these plants but higher in wrky25 mutants compared to wildtype plants, suggesting that WRKY25 itself is involved in controlling intracellular redox conditions [82]. However, not all WRKYs appear to act redox-sensitive: WRKY18 does not show any functional changes under different redox-conditions [82] whereas WRKY70 binding to the W-box 2 of the WRKY53 promoter is more efficient under oxidizing conditions (unpublished results). WRKY53 itself is also redox-sensitive but only to a low extent [82]; however, in protoplasts of wrky53 mutant cells activation of WRKY53 promoter-driven reporter gene expression is almost completely abolished, indicating that the WRKY53 protein itself plays a role in the H 2 O 2 response of its own gene [72].…”

“…Even though MEKK1 can directly bind to DNA, it cannot directly activate transcription, as it has no activation domain per se. Instead, MEKK1 most likely interacts with WRKY53 or other WRKYs proteins that bind to the promoter region of the WRKY53 gene and phosphorylates them, thereby increasing or decreasing their activity [72,82]. Thus, MEKK1 is a bifunctional protein: It can bind DNA and can phosphorylate proteins.…”

A WRKY transcription factor, TaWRKY40‐D, promotes leaf senescence associated with jasmonic acid and abscisic acid pathways in wheat

“…AtWRKY25 can bind directly to the promoter of AtWRKY53 in a redox‐related manner and is thus involved in leaf senescence regulation processes (Doll et al . 2019). AtWRKY45 can interact with the DELLA protein to participate in GA‐induced senescence (Chen et al .…”