Gene response upon illumination in forming mRNA encoding peroxisomal glycollate oxidase.

Glycollate oxidase is a constituent of leaf peroxisomes. Its biosynthesis is, like the biosynthesis of many chloroplastic proteins, controlled by light, via phytochrome. The level of mRNA coding for glycollate oxidase was determined at different stages of greening of etiolated plant cells. The appearance of glycollate oxidase mRNA in the cytoplasm was measured by hybridization with cDNA containing part of the coding sequence for glycollate oxidase. cDNA was prepared from enriched mRNA, inserted into the Pst I site of pBR 322, and cloned in Escherichia coli DH-1. By differential colony hybridization and hybrid selection, a clone containing a 670 bp sequence complementary to mRNA encoding glycollate oxidase was selected and identified. Northern blot hybridization was used to investigate mRNA levels induced by light. It was found that continuous light affected the formation of glycollate oxidase mRNA. When a large population of microbodies was present in the cells being induced, the immediate mRNA increase was very pronounced, and was detectable as little as 20 min after the beginning of the light treatment. In contrast, a lag period in the mRNA increase was observed when the induction was performed with etiolated leaves which are characterized by the occurrence of a rather small population of microbodies. For comparison, we measured the time-course of formation of mRNA coding for a light-induced chloroplastic protein, i.e., a protein of the light-harvesting complex. The time-courses of levels of the two mRNAs indicate that the program of gene expression differs between the two particular proteins destined either for chloroplasts or for peroxisomes. The formation of glycollate oxidase mRNA could also be stimulated by a short pulse of light, a treatment of 15 s being a sufficient trigger.