Arabidopsis Carboxyl-Terminal Domain Phosphatase-Like Isoforms Share Common Catalytic and Interaction Domains But Have Distinct in Planta Functions

Abstract

An Arabidopsis (Arabidopsis thaliana) multigene family (predicted to be more than 20 members) encodes plant C-terminal domain (CTD) phosphatases that dephosphorylate Ser residues in tandem heptad repeat sequences of the RNA polymerase II C terminus. CTD phosphatase-like (CPL) isoforms 1 and 3 are regulators of osmotic stress and abscisic acid (ABA) signaling. Evidence presented herein indicates that CPL3 and CPL4 are homologs of a prototype CTD phosphatase, FCP1 (TFIIFinteracting CTD-phosphatase). CPL3 and CPL4 contain catalytic FCP1 homology and breast cancer 1 C terminus (BRCT) domains. Recombinant CPL3 and CPL4 interact with AtRAP74, an Arabidopsis ortholog of a FCP1-interacting TFIIF subunit. A CPL3 or CPL4 C-terminal fragment that contains the BRCT domain mediates molecular interaction with AtRAP74. Consistent with their predicted roles in transcriptional regulation, green fluorescent protein fusion proteins of CPL3, CPL4, and RAP74 all localize to the nucleus. cpl3 mutations that eliminate the BRCT or FCP1 homology domain cause ABA hyperactivation of the stress-inducible RD29a promoter, whereas RNAi suppression of CPL4 results in dwarfism and reduced seedling growth. These results indicate CPL3 and CPL4 are a paralogous pair of general transcription regulators with similar biochemical properties, but are required for the distinct developmental and environmental responses. CPL4 is necessary for normal plant growth and thus most orthologous to fungal and metazoan FCP1, whereas CPL3 is an isoform that specifically facilitates ABA signaling.

Evolutionary Radiation Pattern of Novel Protein Phosphatases Revealed by Analysis of Protein Data from the Completely Sequenced Genomes of Humans, Green Algae, and Higher Plants

“…Finally, it should be pointed out that for each of the genes in the FCP1-like set, there is a single tissue, or a small set of tissues, which display a greatly enhanced level of expression (with the exception of At3g29760, which shows relatively ubiquitous expression). The limited protein data available (for CPL3 and CPL4) lends some support to this, with expression mostly in the roots, when compared to shoots (Bang et al, 2006). This is in contrast to the other more highly conserved genes in this study (e.g.…”

“…Both of these proteins contain a functional BRCT domain, which binds to AtRAP74, a homolog of animal/yeast TFIIF (Bang et al, 2006). Knockout plants for CPL3 display hyperactivation of abscisic acid (ABA)-mediated transcription, as well as a general alteration of plant growth and maturation, which can be duplicated with mutations to either the BRCT or catalytic domains (Koiwa et al, 2002).…”

“…Because of the well-studied ability of some FCP1-like protein phosphatases to modify the phosphorylation state of RNA Pol II and thus to alter the dynamics of mRNA transcription, Bang et al (2006) suggested that they might be able to act as regulators of gene expression. To investigate this possibility further, we analyzed the Affimetrix microarray expression data available for probes from this gene set.…”

“…Knockout plants for CPL3 display hyperactivation of abscisic acid (ABA)-mediated transcription, as well as a general alteration of plant growth and maturation, which can be duplicated with mutations to either the BRCT or catalytic domains (Koiwa et al, 2002). RNAi knockdown of CPL4 also leads to plant growth and maturation defects (Bang et al, 2006).…”

Mutation in <i>OsLMS</i>, a gene encoding a protein with two double-stranded RNA binding motifs, causes lesion mimic phenotype and early senescence in rice (<i>Oryza sativa</i> L.)

“…The recently reported CTD phosphatase like gene in rice is involved in cell differentiation, and controls abscission layer development and seed shattering (Ji et al, 2010). Of the more than 20 genes in Arabidopsis genome that encode CTD-phosphatase like domain, only four (AtCPL1-AtCPL4) have been isolated and characterized in detail (Bang et al, 2006;Koiwa et al, 2002Koiwa et al, , 2004Ueda et al, 2008;Xiong et al, 2002). In addition to the CTD phosphatase domain, AtCPL1 and AtCPL2 harbor two and a single double-stranded RNA binding motifs (DRM) in their C-terminus, respectively (Ueda et al, 2008).…”