Sucrose sensing through nascent peptide‐meditated ribosome stalling at the stop codon of Arabidopsis bZIP11 uORF2

Abstract

Arabidopsis bZIP11 is a transcription factor that modulates amino acid metabolism under high-sucrose conditions. Expression of bZIP11 is downregulated in a sucrose-dependent manner during translation. Previous in vivo studies have identified the second upstream open reading frame (uORF2) as an essential regulatory element for the sucrose-dependent translational repression of bZIP11. However, it remains unclear how uORF2 represses bZIP11 expression under high-sucrose conditions. Through biochemical experiments using cell-free translation systems, we report on sucrose-mediated ribosome stalling at the stop codon of uORF2. The C-terminal 10 amino acids (29-SFSVxFLxxLYYV-41) of uORF2 are important for ribosome stalling. Our results demonstrate that uORF2 encodes a regulatory nascent peptide that functions to sense intracellular sucrose abundance. This is the first biochemical identification of the intracellular sucrose sensor.

Carbon export from leaves is controlled via ubiquitination and phosphorylation of sucrose transporter SUC2

“…With regard to the control of UBC34, it was found that its promoter contains four predicted binding sites for the GBF6 transcription factor (40), which is light-regulated (41) and can act as a sucrose sensor (42). This provides an exciting hypothesis for the long-proposed link between sucrose levels and SUC2 activity (8,43).…”

Metabolite Control of Translation by Conserved Peptide uORFs: The Ribosome as a Metabolite Multisensor

“…Increasing Suc levels promote ribosome stalling on the CPuORF and, consequently, due to steric hindrance on the 59 leader, ribosomes translating or scanning the uORF are unable to reach and translate the mORF ( Fig. 1; Juntawong et al, 2014;Hou et al, 2016;Yamashita et al, 2017). Single amino acid mutations in the CPuORF abolish Suc-dependent ribosome stalling (Rahmani et al, 2009;Yamashita et al, 2017).…”

“…1; Juntawong et al, 2014;Hou et al, 2016;Yamashita et al, 2017). Single amino acid mutations in the CPuORF abolish Suc-dependent ribosome stalling (Rahmani et al, 2009;Yamashita et al, 2017). Thus, the CPuORF peptide and not the nucleotide sequence plays a role in ribosome stalling.…”

The Dynamic Kaleidoscope of RNA Biology in Plants

“…Suc, polyamines, thermospermine, phosphocholine, ascorbate, galactinol, and boron). The stalling of ribosomes along these CPuORFs or at their stop codons is confirmed in ribosome-footprinting studies and is dependent upon the encoded peptide and metabolic status (Yamashita et al, 2017;van der Horst et al, 2019). Ribosome stalling also can occur in a metabolite-specific manner during mORF translation, as S-adenosyl-L-Met promotes ribosome stalling on CYSTATHIONINE GAMMA SYNTHASE1 (CGS1) mRNA, triggering its degradation.…”