Molecular and functional characterization of two drought-induced zinc finger proteins, ZmZnF1 and ZmZnF2 from maize kernels

Abstract

Zinc finger proteins are among the most abundant proteins in eukaryotic cells. Their functions are diverse, including DNA and RNA banding, transcriptional activation, regulation of apoptosis, protein folding and assembly. We have isolated two cDNA clones encoding zinc finger proteins, designated as ZmZnF1 and ZmZnF2, from water-stressed maize kernels. Sequence analyses indicates that ZmZnF1 is homologous to the A20/AN1-type zinc finger protein and contains the zinc finger motif of Cx2–Cx10–CxCx4Cx2Hx5HxC, whereas ZmZnF2 is a ring-binding type and contains 3 repeats of the Cx-Cx-H-Cx-Cx zinc finger motif. RNA gel blot analyses indicate that both genes were significantly induced by ABA, osmotic stress (mannitol) and NaCl stress. Using an effector-reporter strategy, we transiently expressed ZmZnF1 or ZmZnF2 with the GUS reporter driven by the rice actin1 promoter containing ABA responsive element, ABRC1 in maize suspension cells. Assay of GUS activity showed that both ZmZnF1 and ZmZnF2 activated the reporter gene expression. A synergistic effect on activation was found between ZmZnF2 and another ABA response factor, VP1. These results were confirmed by the complementary test using RNAi technology. Our results suggest that both ZmZnF1 and ZmZnF2 are transcription activators and may play roles in regulating expression of drought-responsive genes or other transcription factors in response to abiotic stress.