Regulation of Reversible Dissociation of LHCII from PSII by Phosphorylation in Plants

Zhenhai Cui,Ao Zhang,Lijun Zhang,Yanpeng Wang

doi:10.4236/ajps.2014.52032

Abstract

LHCII is a crucial light-harvesting pigment/protein complex in photosystem II (PSII) supercomplex. It also participates in the light energy redistribution between photosystems and in the photoprotection via its reversible dissociation with PSII and PSI (photosystem I). This reversible detachment of LHCII is regulated by phosphorylation of its own and PSII core protein. Under low light conditions, LHCII is phosphorylated and dissociated with PSII core protein complex and combined with PSI, which balances the excitation energy between PSII and PSI; Under high light environment, the phosphorylation of PSII core proteins makes LHCII detach from PSII. The dissociated LHCII presents in a free state, which involves in the thermal dissipation of excess excitation energy. During photodamage, dual phosphorylations of both PSII core proteins and LHCII complexes occur. The phosphorylation of D1 is conductive to the disintegration of photodamaged PSII and the cycle of repair. In this circumstance, the phosphorylation of LHCII is induced by reactive oxygen species (ROS) and then the phosphorylated LHCII migrates to PSI, into the repair cycle of damaged PSII. The ferredoxin (Fdr) and thioredoxin (Tdr) system may play a possible central role in the phosphorylation regulation on LHCII dissociation.

Highlights

Photosynthetic organisms utilize sunlight energy, CO2 and H2O to synthesize carbohydrates
The electron transfer chain locates in the membrane of thylakoid, containing the two types of photosystems (PSII, PSI) and cytochrome b6-f (Cytb6-f) complexes
It is suggested that when PSI is over excited under long-wavelength light, PQH2 is oxidized and released from the Qo site, and the phosphatases in stromal side become active and catalyze the dephosphorylation of phosphorylated LHCIIproteins [48, 49], Light-Harvesting Complex II (LHCII) dissociated from photosystem II (PSII)

Summary

Introduction

Photosynthetic organisms utilize sunlight energy, CO2 and H2O to synthesize carbohydrates. Light reaction occurs inside chloroplasts, to generate NADPH and ATP by photosynthetic electron transfer chain and photophosphorylation. The resulting excess energy in photosynthetic apparatus damages PSII complexes and reduces the photosynthetic efficiency. This phenomenon is so-called photoinhibition or photodamage. Under the light condition with changing wavelength, the reversible detachment of LHCII complex makes the excitation energy redistributed between the two photosystems [10,12]. In continuous intensive light condition, a number of LHCIIs dissociate from PSII and present in a free state inside chloroplast stroma, preventing more excitation energy from destroying the reaction centers [13,14]. The reversible dissociation of LHCII with the photosystems is regulated by phosphorylation [6,17], and the mechanism of phosphorylation according to the light intensity

LHCII Phosphorylation in State Transition

Phosphorylation of PSII Core Proteins in Photoprotection

LHCII Phosphorylation in Photodamage

Perspectives