Light regulates alternative splicing of hydroxypyruvate reductase in pumpkin

Hydroxypyruvate reductase (HPR) is a leaf peroxisomal enzyme that functions in the glycolate pathway of photorespiration in plants. We have obtained t wo highly similar cDNAs for pumpkin HPR (HPR1 and HPR2). It has been reveal ed that two HPR mRNAs might be produced by alternative splicing from a sing le type of pre-mRNA. The HPR1 protein, but not the HPR2 protein, was found to have a targeting sequence into leaf peroxisomes at the C-terminus, sugge sting that alternative splicing controls the subcellular localization of th e two HPR proteins. Immunoblot analysis and subcellular fractionation exper iments showed that HPR1 and HPRZ proteins are localized in leaf peroxisomes and the cytosol, respectively. Moreover, indirect fluorescence microscopy and analyses of transgenic tobacco cultured cells and Arabidopsis thaliana expressing fusion proteins with green fluorescent protein (GFP) revealed th e different subcellular localizations of the two HPR proteins. Both mRNAs w ere induced developmentally and by tight, but with quantitative differences . Almost equal amounts of the mRNAs were detected in pumpkin cotyledons gro wn in darkness, but treatment with light greatly enhanced the production of HPR2 mRNA. These findings indicate that light regulates alternative splici ng of HPR mRNA, suggesting the presence of a novel mechanism of mRNA matura tion, namely light-regulated alternative splicing, in higher plants.