The PsbP Protein Is Required for Photosystem II Complex Assembly/Stability and Photoautotrophy in Arabidopsis thaliana

Xiaoping Yi,Stefan R Hargett,Haijun Liu,Laurie K Frankel,Terry M Bricker

doi:10.1074/jbc.m705011200

Abstract

Interfering RNA was used to suppress the expression of the genes At1g06680 and At2g30790 in Arabidopsis thaliana, which encode the PsbP-1 and PsbP-2 proteins, respectively, of photosystem II (PS II). A phenotypic series of transgenic plants was recovered that expressed intermediate and low amounts of PsbP. Chlorophyll fluorescence induction and Q(A)(-) decay kinetics analyses were performed. Decreasing amounts of expressed PsbP protein led to the progressive loss of variable fluorescence and a marked decrease in the fluorescence quantum yield (F(V)/F(M)). This was primarily due to the loss of the J to I transition. Analysis of the fast fluorescence rise kinetics indicated no significant change in the number of PS II(beta) centers present in the mutants. Analysis of Q(A)(-) decay kinetics in the absence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea indicated a defect in electron transfer from Q(A)(-) to Q(B), whereas experiments performed in the presence of this herbicide indicated that charge recombination between Q(A)(-) and the oxygen-evolving complex was seriously retarded in the plants that expressed low amounts of the PsbP protein. These results demonstrate that the amount of functional PS II reaction centers is compromised in the plants that exhibited intermediate and low amounts of the PsbP protein. Plants that lacked detectable PsbP were unable to survive in the absence of sucrose, indicating that the PsbP protein is required for photoautotrophy. Immunological analysis of the PS II protein complement indicated that significant losses of the CP47 and D2 proteins, and intermediate losses of the CP43 and D1 proteins, occurred in the absence of the PsbP protein. This demonstrates that the extrinsic protein PsbP is required for PS II core assembly/stability.

Highlights

Deletion of the genes for these components results in the disassembly of the photosystem II (PS II) complex and the complete loss of oxygen evolution activity
The studies performed in tobacco indicated that RNAi suppression of the PsbQ proteins led to no observable phenotype, but RNAi suppression of the PsbP proteins led to retardation of photoautotrophic growth, lower quantum yield of PS II, loss of PsbQ, and an unstable manganese cluster that disassembled in the dark
Studies performed in Arabidopsis showed that the RNAi suppression of PsbQ led to the impaired assembly/stability of PS II in low light growth conditions, resulting in the loss of photoautotrophy [16]

Summary

Introduction

Deletion of the genes for these components results in the disassembly of the PS II complex and the complete loss of oxygen evolution activity (for review, see Ref. 4). The precise roles of these proteins in oxygen evolution and PS II assembly/stability in vivo, remain unclear These three extrinsic components interact with intrinsic membrane proteins and possibly with each other to yield fully functional oxygen-evolving complexes. Studies performed in Arabidopsis showed that the RNAi suppression of PsbQ led to the impaired assembly/stability of PS II in low light growth conditions, resulting in the loss of photoautotrophy [16]. Our studies differ from those performed in tobacco [18] in that we find, in Arabidopsis, the PsbP protein appears to be required for photoautotrophy and that, in its absence, significant decreases in the amounts of the PS II core proteins D2 and CP47 occur. We provide fluorescence yield data, immunological data, and growth characterization to support the hypothesis that PsbP is required for PS II assembly/ stability and photoautotrophic growth in Arabidopsis

Methods

Results

Conclusion