Abstract：Abstract Photosystem Ⅱ subunit R (PsbR) is a small subunit protein in photosystemⅡ and plays important roles in photosynthetic physiology of plants. To investigate the function of PsbR in winter turnip rape (Brassica campestris), a strong cold-tolerance winter turnip rape cultivar "Longyou 7" was used as experimental materials in this study. The PsbR was separated and cloned from the leaf by differential display reverse transcription PCR(DDRT-PCR) and rapid-amplification of cDNA ends (RACE). The full length cDNA of PsbR was 570 bp and the open reading frame (ORF) encoding a protein of 138 amino acids was 417 bp. The accession number was KC894423 in GenBank. Its molecular mass was 14.39 kD and the isoelectric point (pI) was 9.42. The prediction of the second structures indicated that PsbR was a steady protein and had a transmembrane region and contained a conserved amino acid sequence. PsbR belonged to the PsbR superfamily, which presented high similarity with PsbR proteins from B. oleracea var. oleracea, E. salsugineum and B. juncea. The relative expression of PsbR gene under low temperature stress and the net photosynthetic rate (Pn)and efficiency of primary conversion of light energy of photosystemⅡ(Fv/Fm) in the natural temperature falling were determined with qRT-PCR technology, CIRAS-2 photosynthetic apparatus and FMS-2 pulse modulated fluorometer, respectively. The main results showed that as temperature fell, the expression of PsbR, Pn and Fv/Fm decreased. Therefore, the expression of the PsbR gene may be inhibited under low temperature stress and then decreased net photosynthetic rate and photochemical efficiency of PSⅡ. The results provide a theoretical basis for resolving the biological functions of PsbR and the cold-tolerance molecular mechanism of winter turnip rape.
