UV-B-induced Differential Transcription of psbAGenes Encoding the D1 Protein of Photosystem II in the Cyanobacterium Synechocystis 6803

Zoltán Máté,László Sass,Miklós Szekeres,Imre Vass,Ferenc Nagy

doi:10.1074/jbc.273.28.17439

Abstract

UV-B irradiation of intact Synechocystis sp. PCC 6803 cells results in the loss of photosystem II activity, which can be repaired via de novo synthesis of the D1 (and D2) reaction center subunits. In this study, we investigated the effect of UV-B irradiation on the transcription of the psbA2 and psbA3 genes encoding identical D1 proteins. We show that UV-B irradiation increases the level of psbA2 mRNA 2-3-fold and, more dramatically, it induces a 20-30-fold increase in the accumulation of the psbA3 mRNA even at levels of irradiation too low to produce losses of either photosystem II activity or D1 protein. The induction of psbA3 transcript accumulation is specific for UV-B light (290-330 nm). Low intensity UV-A emission (330-390 nm) and white light induce only a small, at most, 2-3-fold enhancement, whereas no effect of blue light was observed. Expression patterns of chimeric genes containing the promoter regions of the psbA2, psbA3 genes fused to the firefly luciferase (luc) reporter gene indicate that (i) transcription of psbA2/luc and psbA3/luc transgenes was elevated, similarly to that of the endogenous psbA genes, by UV-B irradiation, and that (ii) a short, 80-base pair psbA3 promoter fragment is sufficient to maintain UV-B-induced transcription of the luc reporter gene. Furthermore, our findings indicate that UV-B-induced expression of the psbA2 and psbA3 genes is a defense response against UV-B stress, which is regulated, at least, partially at the level of transcription and does not require active electron transport.

Highlights

Recent reductions in the stratospheric ozone layer allowing more ultraviolet-B (UV-B, 280 –320 nm) radiation to reach the Earth’s surface and ecologically significant depths of the ocean [1] have initiated extensive research efforts to elucidate molecular mechanisms regulating responses of various organisms to UV irradiation [2]
Differential Induction of the psbA Genes by UV-B Light—Repair of PSII via de novo synthesis of the D1 reaction center protein following its damage by UV-B radiation is a multistep process [22]
The effect of UV-B light on the expression of the Synechocystis psbA genes encoding the D1 protein was studied as an approach to gain information about the early steps of the protein repair process that was shown by Sass et al [22] to be required for restoring the activity of the UV-B damaged PSII

Summary

Introduction

Recent reductions in the stratospheric ozone layer allowing more ultraviolet-B (UV-B, 280 –320 nm) radiation to reach the Earth’s surface and ecologically significant depths of the ocean [1] have initiated extensive research efforts to elucidate molecular mechanisms regulating responses of various organisms to UV irradiation [2].

Results

Conclusion