Drought-triggered H2A.Z dynamics at clade A PP2C loci are conserved in plants but exhibit species-specific features

The dynamic deposition and eviction of H2A.Z play a crucial role in regulating gene expression during plant stress responses. Our previous study demonstrated that H2A.Z removal accompanies the drought-induced activation of six clade A Protein Phosphatase 2C (PP2C) genes in sorghum. Here, we show that this eviction is fully reversed upon re-watering, indicating that H2A.Z dynamics are tightly linked to the transcriptional activity of these loci. Similar coupling is observed in both rice and maize: drought reduces H2A.Z levels in seven clade A PP2Cs in maize and in four in rice, suggesting a conserved role for H2A.Z in regulating clade A PP2C genes in monocots. Phylogenetic analysis reveals that the PP2Cs whose activation is linked with H2A.Z removal cluster predominantly within two subgroups (I and III), previously identified as negative regulators of abscisic acid (ABA) signaling. In contrast, ABA- or salt-induced expression of clade A PP2Cs rarely correlates with H2A.Z eviction, implying the involvement of a drought-specific signal triggering H2A.Z removal. We identified SbGBF3 as a potential mediator of this process. SbGBF3 is a transcription factor inducible by drought, salt, and ABA, and physically interacts with the H2A.Z-evicting chromatin remodeler SbINO80. However, since SbGBF3 is also induced by ABA and salt stress, additional factors likely cooperate to confer the observed drought specificity.