Glycolate oxidase-dependent H2O2 production regulates IAA biosynthesis in rice

Background Glycolate oxidase (GLO) is not only a key enzyme in photorespiration but also a major engine for H2O2 production in plants. Catalase (CAT)-dependent H2O2 decomposition has been previously reported to be involved in the regulation of IAA biosynthesis. However, it is still not known which mechanism contributed to the H2O2 production in IAA regulation. Results In this study, we found that in glo mutants of rice, as H2O2 levels decreased IAA contents significantly increased, whereas high CO2 abolished the difference in H2O2 and IAA contents between glo mutants and WT. Further analyses showed that tryptophan (Trp, the precursor for IAA biosynthesis in the Trp-dependent biosynthetic pathway) also accumulated due to increased tryptophan synthetase β (TSB) activity. Moreover, expression of the genes involved in Trp-dependent IAA biosynthesis and IBA to IAA conversion were correspondingly up-regulated, further implicating that both pathways contribute to IAA biosynthesis as mediated by the GLO-dependent production of H2O2. Conclusion We investigated the function of GLO in IAA signaling in different levels from transcription, enzyme activities to metabolic levels. The results suggest that GLO-dependent H2O2 signaling, essentially via photorespiration, confers regulation over IAA biosynthesis in rice plants.

Protein Synthesis in Escherichia coli with Mischarged tRNA

ABSTRACT Two types of aspartyl-tRNA synthetase exist: the discriminating enzyme (D-AspRS) forms only Asp-tRNAAsp, while the nondiscriminating one (ND-AspRS) also synthesizes Asp-tRNAAsn, a required intermediate in protein synthesis in many organisms (but not in Escherichia coli). On the basis of the E. coli trpA34 missense mutant transformed with heterologous ND-aspS genes, we developed a system with which to measure the in vivo formation of Asp-tRNAAsn and its acceptance by elongation factor EF-Tu. While large amounts of Asp-tRNAAsn are detrimental to E. coli, smaller amounts support protein synthesis and allow the formation of up to 38% of the wild-type level of missense-suppressed tryptophan synthetase.