Crop plants face a multitude of diverse abiotic and biotic stresses in the farmers' fields. Although there now exists a considerable knowledge of the underlying mechanisms of response to individual stresses, the crosstalk between response pathways to various abiotic and biotic stresses remains enigmatic. Here, we investigated if the cytotoxic metabolite methylglyoxal (MG), excess of which is generated as a common consequence of many abiotic and biotic stresses, may serve as a key molecule linking responses to diverse stresses. For this, we generated transgenic rice plants overexpressing the entire two-step glyoxalase pathway for MG detoxification. Through assessment of various morphological, physiological and agronomic parameters, we found that glyoxalase-overexpression imparts tolerance towards abiotic stresses like salinity, drought and heat and also provides resistance towards damage caused by the sheath blight fungus (Rhizoctonia solani) toxin phenylacetic acid. We show that the mechanism of observed tolerance of the glyoxalase-overexpressing plants towards these diverse abiotic and biotic stresses involves improved MG detoxification and reduced oxidative damage leading to better protection of chloroplast and mitochondrial ultrastructure and maintained photosynthetic efficiency under stress conditions. Together, our findings indicate that MG may serve as a key link between abiotic and biotic stress response in plants.

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Protein syntheses mediated by cellular and viral internal ribosome entry sites (IRESs) are believed to have many features in common. Distinct mechanisms for ribosome recruitment and preinitiation complex assembly between the two processes have not been identified thus far. Here we show that the methylation status of rRNA differentially influenced the mechanism of 80S complex formation on IRES elements from the cellular sodiumcoupled neutral amino acid transporter 2 (SNAT2) versus the hepatitis C virus mRNA. Translation initiation involves the assembly of the 48S preinitiation complex, followed by joining of the 60S ribosomal subunit and formation of the 80S complex. Abrogation of rRNA methylation did not affect the 48S complex but resulted in impairment of 80S complex assembly on the cellular, but not the viral, IRESs tested. Impairment of 80S complex assembly on the amino acid transporter SNAT2 IRES was rescued by purified 60S subunits containing fully methylated rRNA. We found that rRNA methylation did not affect the activity of any of the viral IRESs tested but affected the activity of numerous cellular IRESs. This work reveals a novel mechanism operating on a cohort of cellular IRESs that involves rRNA methylation for proper 80S complex assembly and efficient translation initiation.Initiation of translation on the majority of the cellular mRNAs is 5Ј cap dependent. This process relies on the recruitment of the 43S initiation complex to the cap structure at the 5Ј end of the mRNA promoted by cap-binding initiation factor eIF4F to form 48S initiation complex and subsequent scanning of the 48S complex across the 5Ј untranslated region (UTR) in search of the initiator AUG codon. This major initiation pathway is widely believed to account for most cellular mRNA translation (19,20). On the other hand, a minor cap-independent initiation pathway relying on the presence of internal ribosome entry sites (IRESs) has been described for a subset of viral mRNAs (for a recent review, see reference 15). Viral IRES-dependent translation has been shown to rely on both canonical and noncanonical interactions between IRES elements, canonical eukaryotic initiation factors (eIFs), IRES trans-acting factors (ITAFs; largely considered to act as noncanonical initiation factors), and 40S ribosomal subunits. As a rule, viral IRES-mediated translation does not require the cap-binding initiation factor eIF4E and in general has reduced requirements for other members of the eIF4F factor/complex (specifically, intact eIF4G) (15, 19). It has been further shown that certain cellular mRNAs may rely on similar translation initiation mechanism (21,23,24). Reports on the IRES elements in cellular mRNAs are emerging on a continuing basis; however, the mechanism(s) of their activation and function remains less well understood.The best-studied viral IRES elements can be assigned (based on their structure and requirements for the canonical initiation factors) to four different types. Type 1 (e.g., poliovirus) and type 2 (e.g., encephalomyocarditis v...