Glyphosate treatment mediates the accumulation of small discrete 5'- and 3'-terminal fragments of 18S rRNA in plant cells.

Under many kinds of stress, eukaryotic cells rapidly decrease the overall translation level of the majority of mRNAs. However, some molecular mechanisms of protein synthesis inhibition like phosphorylation of eukaryotic elongation factor 2 (eEF2), which are known to be functional in animals and yeast, are not implemented in plants. We suggest that there is an alternative mechanism for the inhibition of protein synthesis in plant cells and possibly, in other eukaryotes, which is based on the discrete fragmentation of 18S rRNA molecules within small ribosomal subunits.

Phosphorylation of the alpha-subunit of plant eukaryotic initiation factor 2 prevents its association with polysomes but does not considerably suppress protein synthesis.

Phosphorylation of the α-subunit of eukaryotic initiation factor 2 (eIF2α) and subsequent inhibition of protein synthesis is a major survival response to different stresses in animal and yeast cells. However, the role of this regulatory mechanism in plants is not unambiguously established to date. Here we describe a slight reduction of polysome abundance in Nicotiana benthamiana after the transient expression of a cDNA, AteIF2α(S56D), encoding a phosphomimetic form of Arabidopsis thaliana eIF2α.

Constructing the constitutively active ribosomal protein S6 kinase 2 from Arabidopsis thaliana (AtRPS6K2) and testing its activity in vitro.

Ribosomal protein S6 (RPS6) is the only phosphorylatable protein of the eukaryotic 40S ribosomal subunit. Ribosomes with phosphorylated RPS6 can selectively translate 5'TOP-(5'-terminal oligopyrimidine)-containing mRNAs that encode most proteins of the translation apparatus. The study of translational control of 5'TOP-mRNAs, which are preferentially translated when RPS6 is phosphorylated and cease to be translated when RPS6 is de-phosphorylated, is particularly important.

Evidence That Phosphorylation of the -Subunit of eIF2 Does Not Essentially Inhibit mRNA Translation in Wheat Germ Cell-Free System.

A mechanism based on reversible phosphorylation of the -subunit of eukaryotic initiation factor 2 (eIF2) has been confirmed as an important regulatory pathway for the inhibition of protein synthesis in mammalian and yeast cells, while plants constitute the significant exception. We studied the induction of eIF2 phosphorylation in germinated wheat () embryos subjected to different adverse conditions. Data confirmed that formation of eIF2(P) was not a general response, as no phosphorylation was observed under salt, oxidative, or heat stress.

[Fragment of mRNA coding part that is complementary to region 1638-1650 of wheat 18S rRNA functions as a translational enhancer].

Possible involvement of 18S rRNA fragment 1638-1650 including basements of the helices h44 and h28 and nucleotides of the ribosomal decoding site in the cap-independent translation initiation on plant ribosomes is studied. This rRNA fragment is shown to be accessible for complementary interactions within the 40S ribosomal subunit. It is found that the sequence complementary to the 18S rRNA fragment 1638-1650 is able to enhance efficiency of a reporter mRNA translation when placed just after the initiation codon.