Phylogenetic analysis of F-bZIP transcription factors indicates conservation of the zinc deficiency response across land plants

Basic leucine zipper (bZIP) transcription factors control important developmental and physiological processes in plants. In Arabidopsis thaliana, the three gene F-bZIP subfamily has been associated with zinc deficiency and salt stress response. Benefiting from the present abundance of plant genomic data, we performed an evolutionary and structural characterization of plant F-bZIPs. We observed divergence during seed plant evolution, into two groups and inferred different selective pressures for each. Group 1 contains AtbZIP19 and AtbZIP23 and appears more conserved, whereas Group 2, containing AtbZIP24, is more prone to gene loss and expansion events. Transcriptomic and experimental data reinforced AtbZIP19/23 as pivotal regulators of the zinc deficiency response, mostly via the activation of genes from the ZIP metal transporter family, and revealed that they are the main regulatory switch of AtZIP4. A survey of AtZIP4 orthologs promoters across different plant taxa revealed an enrichment of the Zinc Deficiency Response Element (ZDRE) to which both AtbZIP19/23 bind. Overall, our results indicate that while the AtbZIP24 function in the regulation of the salt stress response may be the result of neo-functionalization, the AtbZIP19/23 function in the regulation of the zinc deficiency response may be conserved in land plants (Embryophytes).