Glycolate oxidase-dependent HO production regulates IAA biosynthesis in rice.

Background: Glycolate oxidase (GLO) is not only a key enzyme in photorespiration but also a major engine for HO production in plants. Catalase (CAT)-dependent HO 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 HO production in IAA regulation.

Results: In this study, we found that in glo mutants of rice, as HO levels decreased IAA contents significantly increased, whereas high CO abolished the difference in HO 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 HO.

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 HO signaling, essentially via photorespiration, confers regulation over IAA biosynthesis in rice plants.