LLM-Domain Containing B-GATA Factors Control Different Aspects of Cytokinin-Regulated Development in Arabidopsis thaliana.

Leu-Leu-Met (LLM)-domain B-GATAs are a subfamily of the 30-membered GATA transcription factor family from Arabidopsis. Only two of the six Arabidopsis LLM-domain B-GATAs, i.e. GATA, NITRATE-INDUCIBLE, CARBON METABOLISM-INVOLVED (GNC) and its paralog GNC-LIKE/CYTOKININ-RESPONSIVE GATA FACTOR1 (GNL), have already been analyzed with regard to their biological function. Together, GNC and GNL control germination, greening, flowering time, and senescence downstream from auxin, cytokinin (CK), gibberellin (GA), and light signaling. Whereas overexpression and complementation analyses suggest a redundant biochemical function between GNC and GNL, nothing is known about the biological role of the four other LLM-domain B-GATAs, GATA15, GATA16, GATA17, and GATA17L (GATA17-LIKE), based on loss-of-function mutant phenotypes. Here, we examine insertion mutants of the six Arabidopsis B-GATA genes and reveal the role of these genes in the control of greening, hypocotyl elongation, phyllotaxy, floral organ initiation, accessory meristem formation, flowering time, and senescence. Several of these phenotypes had previously not been described for the gnc and gnl mutants or were enhanced in the more complex mutants when compared to gnc gnl mutants. Some of the respective responses may be mediated by CK signaling, which activates the expression of all six GATA genes. CK-induced gene expression is partially compromised in LLM-domain B-GATA mutants, suggesting that B-GATA genes play a role in CK responses. We furthermore provide evidence for a transcriptional cross regulation between these GATAs that may, in at least some cases, be at the basis of their apparent functional redundancy.