Glycolate oxidase-dependent H 2 O 2 production regulates IAA biosynthesis in rice

Background Glycolate oxidase (GLO) is not only a key enzyme in photorespiration but also a major engine for H 2 O 2 production in plants. Catalase (CAT)-dependent H 2 O 2 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 H 2 O 2 production in IAA regulation. Results In this study, we found that in glo mutants of rice, as H 2 O 2 levels decreased IAA contents significantly increased, whereas high CO 2 abolished the difference in H 2 O 2 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 H 2 O 2 . 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 H 2 O 2 signaling, essentially via photorespiration, confers regulation over IAA biosynthesis in rice plants.