Zinc-finger proteins: the classical zinc finger emerges in contemporary plant science

TFIIIA-type zinc fingers have been found in a number of eucaryotic transcription factors as DNA-binding motifs. In plants, as many as 30 proteins have been reported that have either one, two, three or four zinc fingers. Plant zinc-finger proteins are characterized by long spacers of diverse lengths between adjacent fingers and a highly conserved sequence, QALGGH, located within a putative DNA-contacting surface of each finger. In vitro DNA-binding experiments with two-fingered proteins of petunia have revealed that these proteins bind to target DNA sequences in a manner that is distinctive from that of their animal counterparts: (1) they specifically recognize the spacing between two core sites in target DNA, (2) they have a unique base-determinant position. Regulatory functions have been assigned to some of the TFIIIA-type zinc finger proteins in Arabidopsis, petunia and chinese cabbage. SUPERMAN, AtZFP1, PetSPL3 and BcZFP1 have been implicated in the developmental regulation of various floral and vegetative organs, presumably through the control of cell division and/or expansion in particular cell types. Several anther-specific zinc-finger proteins in petunia are presumed to be involved in the regulation of gametogenesis in both reproductive and non-reproductive tissues of anther. STZ and ZPT2-2 are implicated in the response of plants to or tolerance for various stresses.