The late steps of plant nonsense‐mediated mRNA decay

Abstract

These authors contributed equally to this work. SUMMARYNonsense-mediated mRNA decay (NMD) is a eukaryotic quality control system that identifies and degrades mRNAs containing premature termination codons (PTCs). If translation terminates at a PTC, the UPF1 NMD factor binds the terminating ribosome and recruits UPF2 and UPF3 to form a functional NMD complex, which triggers the rapid decay of the PTC-containing transcript. Although NMD deficiency is seedling lethal in plants, the mechanism of plant NMD remains poorly understood. To understand how the formation of the NMD complex leads to transcript decay we functionally mapped the UPF1 and SMG7 plant NMD factors, the putative key players of NMD target degradation. Our data indicate that the cysteine-histidine-rich (CH) and helicase domains of UPF1 are only essential for the early steps of NMD, whereas the heavily phosphorylated N-and C-terminal regions play a redundant but essential role in the target transcript degradation steps of NMD. We also show that both the N-and the C-terminal regions of SMG7 are essential for NMD. The N terminus contains a phosphoserine-binding domain that is required for the early steps of NMD, whereas the C terminus is required to trigger the degradation of NMD target transcripts. Moreover, SMG7 is a P-body component that can also remobilize UPF1 from the cytoplasm into processing bodies (P bodies). We propose that the N-and C-terminal phosphorylated regions of UPF1 recruit SMG7 to the functional NMD complex, and then SMG7 transports the PTC-containing transcripts into P bodies for degradation.

BnaC9.SMG7b functions as a positive regulator of number of seeds per silique in rapeseed (Brassica napus L.) by regulating the formation of functional female gametophytes

“…There are two possible reasons for this functional divergence of BnaC9.SMG7b. First, the N-terminal EST1-TPR domain of SMG7 contains a phospho-Ser binding domain that is required for the early steps of NMD (Fukuhara et al, 2005;Mérai et al, 2013), whereas this conserved domain is nearly completely deleted in BnaC9.SMG7b (Supplemental Fig. S2).…”

“…Processing bodies (P bodies) are small cytoplasmic foci that contain all NMD factors, including SMG7 in eukaryotes (Eulalio et al, 2007;Riehs, 2009;Kulkarni et al, 2010;Mérai et al, 2013). To investigate the subcellular localization of BnaC9.SMG7b, we fused the coding region of BnaC9.SMG7b with the coding region of an enhanced GFP driven by a Cauliflower mosaic virus 35S promoter.…”

“…To investigate the subcellular localization of BnaC9.SMG7b, we fused the coding region of BnaC9.SMG7b with the coding region of an enhanced GFP driven by a Cauliflower mosaic virus 35S promoter. This chimeric plasmid and a P bodies marker (Arabidopsis DECAPPING COMPLEX PROTEIN1 [AtDCP1]; Mérai et al, 2013) were cotransformed into Arabidopsis protoplasts. The results showed that the BnaC9.SMG7b-GFP fusion protein was colocalized with the marker in the P bodies (Fig.…”

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

“…It was proposed that AtSMG7 recruits the NMD complex to PBs for mRNA degradation through its interaction with phosphorylated AtUPF1. However, the mechanism by which NMD targets are fully degraded to nucleotides is unknown, since AtXRN4, the functional cytoplasmic ortholog of mammalian XRN1, is not required Mérai et al, 2013).…”

The RNA Polymerase II C-Terminal Domain Phosphatase-Like Protein FIERY2/CPL1 Interacts with eIF4AIII and Is Essential for Nonsense-Mediated mRNA Decay in Arabidopsis

“…In plants, in addition to the UPF1-3 proteins, orthologs of SMG7, SMG1, and the four core EJC components have been experimentally identified (Lloyd and Davies, 2013;Mérai et al, 2013;Nyikó et al, 2013;Shaul, 2015). Some of the regulatory steps of NMD have also been identified.…”