Identification of a novel chloroplast-localised cyclophilin involved in photosynthetic acclimation

Abstract

In order to maximise light capture during limiting light conditions and to prevent the harmful effects of high irradiance, plants have evolved elaborate mechanisms by which levels of photosynthetic proteins are regulated in response to environmental change. Low light grown plants are characterised by high levels of LHCII and a reduction in the amounts of electron transport components and Rubisco whereas in high light plants the situation is reversed. To identify proteins involved in photosynthetic acclimation to low light, a differential display screen was carried out using mRNA from Arabidopsis plants grown in high light (400µmol.m-2.s-1) and transferred to low light (100µmol.m-2.s-1). A transcript encoding a novel chloroplast localised cyclophilin (ROC8) was found to be up-regulated during this transient. ROC8 protein levels also increase and as expected the protein is only expressed in photosynthetic tissue. Recombinant ROC8 possesses cyclosporin-sensitive peptidyl-prolyl cis-trans isomerase activity. Initial analysis of antisense ROC8 lines show slowed development and reduced levels of chlorophyll. In humans, cyclophilins have been shown to play a number of important roles in signal transduction but little is known about their role in plants. These data suggest that ROC8 may play an important role during acclimation of photosynthesis to the environment.