Abstract
Nonsense-mediated mRNA decay (NMD) is a eukaryotic RNA surveillance mechanism that degrades aberrant transcripts and controls the levels of many normal mRNAs. It was shown that balanced expression of the NMD factor UPF3 is essential for the maintenance of proper NMD homeostasis in Arabidopsis. UPF3 expression is controlled by a negative feedback loop that exposes UPF3 transcript to NMD. It was shown that the long 3′ untranslated region (3′ UTR) of UPF3 exposes its transcript to NMD. Long 3′ UTRs that subject their transcripts to NMD were identified in several eukaryotic NMD factors. Interestingly, we show here that a construct that contains all the regulatory regions of the UPF3 gene except this long 3′ UTR is also feedback-regulated by NMD. This indicates that UPF3 expression is feedback-regulated at multiple levels. UPF3 is constitutively expressed in different plant tissues, and its expression is equal in leaves of plants of different ages. This finding is in agreement with the possibility that UPF3 is ubiquitously operative in the Arabidopsis NMD pathway. Expression mediated by the regulatory regions of UPF3 is significantly induced by salt stress. We found that both a deficiency and a strong excess of UPF3 expression are detrimental to plant resistance to salt stress. This indicates that UPF3 plays a role in plant response to salt stress, and that balanced expression of the UPF3 gene is essential for coping with this stress.
Highlights
Nonsense-mediated mRNA decay (NMD) is an RNA surveillance mechanism that functions in all eukaryotes
We showed that the maintenance of balanced expression of the Arabidopsis UPF3 gene is very important for the overall regulation of plant NMD (Degtiar et al, 2015)
We showed that UPF3 is controlled by a negative feedback loop that increases its expression when NMD is inhibited, and restricts its expression when NMD functions properly (Saul et al, 2009)
Summary
Nonsense-mediated mRNA decay (NMD) is an RNA surveillance mechanism that functions in all eukaryotes (reviewed by Celik et al, 2015; Fatscher et al, 2015; He and Jacobson, 2015; Shaul, 2015; Smith and Baker, 2015). Normal translation termination and ribosome recycling, Regulation of the Arabidopsis UPF3 Gene which prohibit NMD, depend on the interaction between eRF3 and the poly(A)-binding protein (PABP; Fatscher et al, 2014; Joncourt et al, 2014). This can shed light on the question of whether UPF3 is ubiquitously utilized in the NMD of wild type (WT) plants or, alternatively, if there are certain tissues or growth stages in which a UPF3-independent branch of the NMD pathway is normally operative The latter situation is possible, since Arabidopsis plants with a null mutation in the UPF3 gene are viable. Our finding that a construct including UPF3 regulatory regions but lacking its long 3 UTR is controlled by NMD, indicates that UPF3 expression is feedback-regulated by NMD at multiple levels. This indicates that UPF3 plays a role in plant response to salt stress, and that the balanced expression of the UPF3 gene is essential for coping with this stress
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