SppA is new protease component of thylakoid membranes involved in the light acclimation

Abstract

A new component of the chloroplast proteolytic machinery from Arabidopsis thaliana was identified as an SppA-type protease. Subfractionation of intact chloroplasts demonstrated that SppA is associated exclusively with thylakoid membranes and behaves as an intrinsic membrane protein which may have an unusual monotopic arrangement in the thylakoids. We showed that SppA is a light-inducible protein in higher plants on both transcriptional and posttranslational levels. The physiological role of this component was studied on the strain disrupted in protease gene sppA1 in Synechocystis sp. PCC 6803. DsppA1 mutant strain demonstrated the loss of some adaptation mechanisms to various light intensities, that resulted in the reduced degradation of phycobilisome antenna, visualized as a less bleaching phenotype under middle light intensities (150 µE m-2 s-1), but rapidly bleaching when transferred to strong light regimes (700 µE m-2 s-1). The fluorescence and biochemical analysis of PSII and phycobilisome antenna in the mutant strain proved that the amount of attached to the PSII phycobilisomes is higher than in the wild type. We discuss the possible involvement of SppA component in the degradation of antenna and PSII core complexes that both involve serine-type protease in higher plants.