Abstract
SummaryPoly(A) tail shortening is a critical step in messenger RNA (mRNA) decay and control of gene expression. The carbon catabolite repressor 4 (CCR4)‐associated factor 1 (CAF1) component of the CCR4‐NOT deadenylase complex plays an essential role in mRNA deadenylation in most eukaryotes. However, while CAF1 has been extensively investigated in yeast and animals, its role in plants remains largely unknown. Here, we show that the Citrus sinensis CAF1 (CsCAF1) is a magnesium‐dependent deadenylase implicated in resistance against the citrus canker bacteria Xanthomonas citri. CsCAF1 interacted with proteins of the CCR4‐NOT complex, including CsVIP2, a NOT2 homologue, translin‐associated factor X (CsTRAX) and the poly(A)‐binding proteins CsPABPN and CsPABPC. CsCAF1 also interacted with PthA4, the main X. citri effector required for citrus canker elicitation. We also present evidence suggesting that PthA4 inhibits CsCAF1 deadenylase activity in vitro and stabilizes the mRNA encoded by the citrus canker susceptibility gene CsLOB1, which is transcriptionally activated by PthA4 during canker formation. Moreover, we show that an inhibitor of CsCAF1 deadenylase activity significantly enhanced canker development, despite causing a reduction in PthA4‐dependent CsLOB1 transcription. These results thus link CsCAF1 with canker development and PthA4‐dependent transcription in citrus plants.
Highlights
Polyadenylation of the 3′ end of messenger RNAs is a coordinated RNA modification process that plays fundamental roles in mRNA transport, stability and processing, and in translational control (Fasken et al, 2008; Millevoi and Vagner, 2010; Weill et al, 2012)
We present evidence suggesting that PthA4 inhibits Citrus sinensis CCR4-associated factor 1 (CAF1) (CsCAF1) deadenylase activity and stabilizes the CsLOB1 mRNA in Xanthomonas citri (Xc)-infected leaves
Sweet orange leaves were infiltrated with Xanthomonas aurantifolii pathotype C (Xa), Xc or water, as control, and the expression of CsCAF1 was monitored by quantitative RTPCR
Summary
Polyadenylation of the 3′ end of messenger RNAs (mRNAs) is a coordinated RNA modification process that plays fundamental roles in mRNA transport, stability and processing, and in translational control (Fasken et al, 2008; Millevoi and Vagner, 2010; Weill et al, 2012). The reverse process, known as deadenylation of the mRNA poly(A) tail, represents a critical translational control mechanism and it is regarded as the first step in mRNA decay (Temme et al, 2014). Besides its role in mRNA deadenylation and decay, the CCR4-NOT complex has been implicated in a variety of cellular processes, including micro RNA (miRNA)-mediated gene silencing, transcriptional elongation and DNA repair (Collart, 2016; Denis et al, 2001; Fabian and Sonenberg, 2012; Gaillard et al, 2009; Kruk et al, 2011). Recent studies in yeast using reconstituted CCR4-NOT complex have revealed that while CCR4 is a general deadenylase that degrades PABP1-bound poly(A) tails, CAF1 is required for the selective deadenylation of transcripts not bound by PABP1 and with lower rates of translation elongation (Webster et al, 2018; Yi et al, 2018). As new evidence emerges, the CCR4-NOT complex has been regarded as a macromolecular structure that connects transcription to translation, and determines the translational capacity of WILEY & SONS LTD
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