Arabidopsis Deadenylases AtCAF1a and AtCAF1b Play Overlapping and Distinct Roles in Mediating Environmental Stress Responses

Abstract

To maintain homeostasis in an ever-changing environment organisms have evolved mechanisms to reprogram gene expression. One central mechanism regulating gene expression is messenger RNA (mRNA) degradation, which is initiated by poly(A) tail shortening (deadenylation). The carbon catabolite repressor 4-CCR4 associated factor1 (CCR4-CAF1) complex is the major enzyme complex that catalyzes mRNA deadenylation and is conserved among eukaryotes. However, the components and functions of this global regulatory complex have not been well characterized in plants. Here we investigate the CAF1 family in Arabidopsis (Arabidopsis thaliana). We identify 11 AtCAF1 homologs and show that a subset of these genes are responsive to mechanical wounding, among them are AtCAF1a and AtCAF1b whose expression levels are rapidly and transiently induced by wounding. The differential expression profiles of the various AtCAF1s suggest that not all AtCAF1 genes are involved in stress-responsive regulation of transcript levels. Comparison of misexpressed genes identified via transcript profiling of Atcaf1a and Atcaf1b mutants at different time points before and after wounding suggests that AtCAF1a and AtCAF1b target shared and unique transcripts for deadenylation with temporal specificity. Consistent with the AtPI4Kγ3 transcript exhibiting the largest increase in abundance in Atcaf1b, AtCAF1b targets AtPI4Kγ3 mRNA for deadenylation. Stress-tolerance assays demonstrate that AtCAF1a and AtCAF1b are involved in mediating abiotic stress responses. However, AtCAF1a and AtCAF1b are not functionally redundant in all cases, nor are they essential for all environmental stresses. These findings demonstrate that these closely related proteins exhibit overlapping and distinct roles with respect to mRNA deadenylation and mediation of stress responses.

Polysomes, Stress Granules, and Processing Bodies: A Dynamic Triumvirate Controlling Cytoplasmic mRNA Fate and Function

“…The expansive Arabidopsis CAF1 family includes 11 members. The products of two of these, CAF1a and CAF1b, exhibit 39-59 exonucleolytic activity in vitro via their conserved DEDD domain, contribute to effective defense response (Liang et al, 2009), and regulate the poly(A) length of a defined set of stress-related transcripts rather than acting as general deadenylases (Liang et al, 2009;Walley et al, 2010).…”

The Ccr4–Not complex

“…In this organism it is interesting to note that RNAi targeting of Caf1 but not Ccr4 leads to an embryonic lethal phenotype (Maeda et al, 2001;Molin and Puisieux, 2005). In plants very few experiments have addressed the role of the Ccr4-Not complex, but in Arabidobsis 2 of the numerous Caf1 homologs play distinct but overlapping roles in response to various environmental stresses (Walley et al, 2010). Male caf1-knockout mice have high bone mass (Washio-Oikawa et al, 2007), compatible with the observation that Caf1 (CNOT7) is expressed in osteoblasts and is associated with mineralization (Washio-Oikawa et al, 2006).…”

Plastid Genome Instability Leads to Reactive Oxygen Species Production and Plastid-to-Nucleus Retrograde Signaling in Arabidopsis

“…Several of the 50 most overexpressed genes in why1why3polIb-1 encode key components of the abiotic stress responses, including the Early Light-Inducible Protein ELIP1, the transcriptional regulators C2/H2-type zinc-finger Arabidopsis transcription factor10 and -12 (ZAT10 and ZAT12), the ERF/AP2 transcription factor C-Repeat DRE/binding factor2 (CBF2), and the mRNA deadenylases CCR4-associated factor1A and -1B (CAF1A and CAF1B; Gilmour et al, 1998;Hutin et al, 2003;Sakamoto et al, 2004;Davletova et al, 2005;Mittler et al, 2006;Walley et al, 2010). Not surprisingly, a striking similarity was observed when comparison was made with overexpressed genes in abiotic stress responses.…”