LOW PHOTOSYNTHETIC EFFICIENCY 1 is required for light-regulated photosystem II biogenesis in Arabidopsis

Significance

Photosystem II (PSII) reaction center protein D1 is encoded by chloroplast gene psbA and is crucial to the biogenesis and functional maintenance of PSII. D1 proteins are highly dynamic under varying light conditions and thus require efficient synthesis, but the mechanism remains poorly understood. We reported that Arabidopsis LPE1 directly binds to the 5′ UTR of psbA mRNA in a light-dependent manner through a redox-based mechanism and facilitates the association of HCF173 with psbA mRNA to regulate D1 translation. These findings fill a major gap in our understanding of the mechanism of light-regulated D1 synthesis in higher plants and imply that higher plants and primitive photosynthetic organisms share conserved mechanisms but use distinct regulators to regulate biogenesis of PSII subunits.

Abstract

Photosystem II (PSII), a multisubunit protein complex of the photosynthetic electron transport chain, functions as a water-plastoquinone oxidoreductase, which is vital to the initiation of photosynthesis and electron transport. Although the structure, composition, and function of PSII are well understood, the mechanism of PSII biogenesis remains largely elusive. Here, we identified a nuclear-encoded pentatricopeptide repeat (PPR) protein LOW PHOTOSYNTHETIC EFFICIENCY 1 (LPE1; encoded by At3g46610) in Arabidopsis, which plays a crucial role in PSII biogenesis. LPE1 is exclusively targeted to chloroplasts and directly binds to the 5′ UTR of psbA mRNA which encodes the PSII reaction center protein D1. The loss of LPE1 results in less efficient loading of ribosome on the psbA mRNA and great synthesis defects in D1 protein. We further found that LPE1 interacts with a known regulator of psbA mRNA translation HIGH CHLOROPHYLL FLUORESCENCE 173 (HCF173) and facilitates the association of HCF173 with psbA mRNA. More interestingly, our results indicate that LPE1 associates with psbA mRNA in a light-dependent manner through a redox-based mechanism. This study enhances our understanding of the mechanism of light-regulated D1 synthesis, providing important insight into PSII biogenesis and the functional maintenance of efficient photosynthesis in higher plants.