B-GATA factors are required to repress high-light stress responses in Marchantia polymorpha and Arabidopsis thaliana.

GATAs are evolutionarily conserved zinc-finger transcription factors from eukaryotes. In plants, GATAs can be subdivided into four classes, A-D, based on their DNA-binding domain, and into further subclasses based on additional protein motifs. B-GATAs with a so-called leucine-leucine-methionine (LLM)-domain can already be found in algae. In angiosperms, the B-GATA family is expanded and can be subdivided in to LLM- or HAN-domain B-GATAs. Both, the LLM- and the HAN-domain are conserved domains of unknown biochemical function. Interestingly, the B-GATA family in the liverwort Marchantia polymorpha and the moss Physcomitrium patens is restricted to one and four family members, respectively. And, in contrast to vascular plants, the bryophyte B-GATAs contain a HAN- as well as an LLM-domain. Here, we characterise mutants of the single B-GATA from Marchantia polymorpha. We reveal that this mutant has defects in thallus growth and in gemma formation. Transcriptomic studies uncover that the B-GATA mutant displays a constitutive high-light (HL) stress response, a phenotype that we then also confirm in mutants of Arabidopsis thaliana LLM-domain B-GATAs, suggesting that the B-GATAs have a protective role towards HL stress.