The Arabidopsis homologs of CCR4-associated factor 1 show mRNA deadenylation activity and play a role in plant defence responses

Abstract

Messenger RNA (mRNA) turnover in eukaryotic cells begins with shortening of the poly (A) tail at the 3′ end, a process called deadenylation. In yeast, the deadenylation reaction is predominantly mediated by CCR4 and CCR4-associated factor 1 (CAF1), two components of the well-characterised protein complex named CCR4-NOT. We report here that AtCAF1a and AtCAF1b, putative Arabidopsis homologs of the yeast CAF1 gene, partially complement the growth defect of the yeast caf1 mutant in the presence of caffeine or at high temperatures. The expression of AtCAF1a and AtCAF1b is induced by multiple stress-related hormones and stimuli. Both AtCAF1a and AtCAF1b show deadenylation activity in vitro and point mutations in the predicted active sites disrupt this activity. T-DNA insertion mutants disrupting the expression of AtCAF1a and/or AtCAF1b are defective in deadenylation of stress-related mRNAs, indicating that the two AtCAF1 proteins are involved in regulated mRNA deadenylation in vivo. Interestingly, the single and double mutants of AtCAF1a and AtCAF1b show reduced expression of pathogenesis-related (PR) genes PR1 and PR2 and are more susceptible to Pseudomonas syringae pv tomato DC3000 (Pst DC3000) infection, whereas transgenic plants over-expressing AtCAF1a show elevated expression of PR1 and PR2 and increased resistance to the same pathogen. Our results suggest roles of the AtCAF1 proteins in regulated mRNA deadenylation and defence responses to pathogen infections.

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

“…Initially, it was reported that a pepper CAF1 homolog, CaCAF1, is required for resistance to the pathogen Xanthomonas axonopodis pv vesicatoria (Sujon et al, 2007). Additionally, Liang et al (2009) reported recently that AtCAF1a and AtCAF1b act redundantly in defense against the pathogen P. syringae pv tomato DC3000, which correlates with reduced levels on PR1 expression in nontreated Atcaf1 mutant plants. Consistently, we also assayed the steady-state levels of PR1 via qRT-PCR and found reduced levels in both Atcaf1a-1 and Atcaf1b-2 plants (data not shown).…”

“…Additionally, it was recently shown that both AtCAF1a and AtCAF1b are required for resistance to the pathogen Pseudomonas syringae (Liang et al, 2009). We therefore chose to test both Atcaf1a and Atcaf1b mutants for tolerance to various environmental stresses.…”

“…It has previously been shown that AtCAF1a and AtCAF1b respond rapidly and transiently to a range of stimuli including mechanical wounding, methyl jasmonate, abscisic acid, 1-aminocyclopropane-1-carboxylic acid, salicylic acid, and Pseudomonas syringae pv tomato DC3000 (Walley et al, 2007;Liang et al, 2009). To determine if stress-induced transcriptional activation of AtCAF1a and AtCAF1b was unique or a general property of all 11 family members, we examined the expression of AtCAF1a to AtCAF1k in response to mechanical wounding by quantitative reverse transcription (qRT)-PCR.…”

“…Furthermore, in Arabidopsis it has been demonstrated that two yeast CAF1 homologs, AtCAF1a (At3g44260) and AtCAF1b (At5g22250), are active deadenylases in vitro and partially complement growth defects of a yeast caf1 deletion strain. Finally, Arabidopsis mutant lines Atcaf1a-1 and Atcaf1b-1 are susceptible to Pseudomonas syringae pv tomato DC3000 (Liang et al, 2009).…”

“…However, the studies that have been conducted focus on CAF1 and demonstrate a role for CAF1 in both development as well as response to biotic stresses. In Arabidopsis, AtCAF1 homologs have been shown to be induced by hormone treatment as well as abiotic and biotic stresses (Lee et al, 2005;Zheng et al, 2006;Ferrari et al, 2007;Walley et al, 2007;Liang et al, 2009). Additionally, one study found that overexpression of a yeast CAF1 homolog from pepper (Capsicum annuum; CaCAF1) in tomato (Solanum lycopersicum) resulted in growth enhancement and resistance to the oomycete pathogen Phytophthora infestans.…”