Polyamine homeostasis in plants: The role(s) of evolutionarily conserved upstream ORFs

Abstract

Cellular polyamine (PA) concentrations are strictly controlled by complex regulatory processes that occur during the synthesis, catabolism, and transport of this compound. These processes include translational repression mediated by upstream open reading frames (uORFs) found in the mRNAs of genes involved in PA metabolism. First, we discuss the roles of dual uORFs in the S -adenosylmethionine decarboxylase gene. Second, we summarize the role of the fourth uORF in a basic helix-loop-helix transcription factor gene, SAC51, in thermospermine action in terms of its effect on xylem vessel differentiation and stem growth. Third, we discuss the sequence-conserved uORFs found in polyamine oxidase (PAO) transcripts encoding peroxisome-localized PAOs. It is currently unclear whether these uORFs cause the repression of PAO translation. Finally, because uORF-mediated repression of arginine decarboxylase (ADC) translation was reported in carnation, we critically assess the role of uORF in ADC translation.