ATAF1 IS A NOVEL SUBSTRATE OF SnRK2 KINASES

SEB Annual Conference -2026

Kinase-catalyzed phosphorylation of proteins defines the principal axes of signal transduction within the cell, coordinating processes such as stress response and growth. Water deprivation and salinity inducer apid phosphorylation cascades involving networks of protein kinases and phosphatases. Among these, Sucrose Non-Fermenting 1 Related Protein Kinases (SnRK2s) are key regulators. SnRK2s are plant-specific enzymes widely distributed across the plant kingdom, controlling both abscisic acid (ABA)-dependent and ABA-independent osmotic stress signaling pathways. Elucidating the substrates of SnRK2 kinases and the functional consequences of their phosphorylation enhances understanding of mechanisms underlying plant stress resistance. While many substrates of ABA-responsive SnRK2 kinases have been identified,relatively few phosphorylation targets of ABA non-activated SnRK2s are known. In this study, a new substrate of SnRK2s, the ATAF1 transcription factor, is identified. ATAF1 is a major regulator of plant responses to a biotic and biotic stress factors, including drought and pathogen attack, as well as a regulator of leaf senescence and light responses. Here, we show that ATAF1 is phosphorylated in vitro by both ABA-activated and non-activated SnRK2 kinases. Phosphorylation ofATAF1 by SnRK2s from salt-treated doublesnrk2.2/2.3mutant is significantly reduced compared to wild-type seedlings, and is nearly absent in the quadruplesnrk2.1/2.4/2.5/2.10mutant. Next, we identified the specific phosphorylation site in ATAF1 recognized bySnRK2s and showed that its phosphorylation determines the protein's cellular localization. Finally, we investigated the impact of ATAF1phosphorylation on plant growth and response to water deprivation.