TZF proteins are characterized by two CCCH Zinc Finger motifs arranged in tandem. In animals, TZFs can localize to specialized cytoplasmic RNA processing centers (Processing Bodies and Stress Granules), and control a variety of cellular processes via the regulation of gene expression at post-transcriptional level. The best characterized TZF so far is human tristetraproline (hTTP). hTTP can regulate mRNA stability by binding to the AU-rich elements in the 3’ untranslated region of target mRNAs and inducing rapid RNA turnover through the recruitment and activation of RNA decay machinery. While TZF functions have been revealed in animals, the functions of plant TZFs remain largely unknown. In Arabidopsis thaliana, there are 11 TZF genes (AtTZF) that contain a TZF motif variant unique to plants. Using a variety of molecular, biochemical, and in silico techniques. I investigated the possible roles for AtTZF function in plants, and compared my results to reports from other eukaryotic TZF proteins. Similar to the TZF genes in animals, I show that AtTZFs in plants can co-localize with, DCP2, AGO1, and XRN4 mRNA processing factors in cytoplasmic foci that resemble plant Processing Bodies and Stress Granules. However, unlike hTTP that can bind RNA through its central TZF domain, AtTZF1 affinity for RNA and DNA requires an additional upstream region characterized by a conserved motif unique to plant TZFs. In silico structural analysis of the AtTZF1 zinc finger motif reveals further differences between animal and plant TZFs suggesting that AtTZFs may bind RNA targets different from those of animal TZFs. Consistent with these differences in structure, I show that AtTZF1 does not bind to the hTTP consensus RNA binding sites.
Though the precise molecular mechanism underlying AtTZF1’s function remains unclear, I show that the expression of AtTZF1 in plants has profound effects on many aspects of ABA and GA mediated growth, development and stress responses. AtTZF1 overexpression (OE) causes reduced sensitivity to light dependent seed germination signals, and confers plants with enhanced drought and cold tolerance. Despite exhibiting many ABA and GA related phenotypes, AtTZF1 OE plants show no significant difference in ABA or GA accumulation when compared to the wild-type plants. Instead, microarray analysis reveals that AtTZF1 specifically affects the expression of several co-expressed ABA and GA responsive gene clusters. Together these results suggest that AtTZF1 can affect plant hormone response via regulation of gene expression.