Abstract: 【Objective】 High light (HL) stress inhibits plant photosynthesis. Severe HL stress will destroy photosynthetic potential, affecting crop growth and production. The objective of this study was to investigate the physiological function of rice ABC1 (activity of bc1 complex) kinase gene OsABC1K3 in HL stress response pathway. 【Method】 To verify the alternative splicing forms of OsABC1K3, 3′ RACE was performed using primers designed from common sequences of different OsABC1K3 transcripts predicted in the Rice Genome Annotation Project Database. Subsequently, a T-DNA insertion mutant of the gene, osabc1k3, was obtained from the Rice T-DNA Insertion Sequence Database. The homozygous mutants were identified by adding-generation propagation and PCR. Then, the mutant agronomic traits such as plant height, seed setting rate and seed size were examined. The leaf pigment contents were determined according to the method of Arnon. The leaf photosynthetic rate and chloroplast ultrastructure were analyzed using a LI-6400 portable photosynthesis measurement system and transmission electron microscopy, respectively. To perform HL treatment, wild type and mutant seedlings grown at 300 μmol·m^-2·s^-1 light intensity were transferred into 800 μmol·m^-2·s^-1. The plant phenotype was photographed, and the variation of chloroplast ultrastructure and chlorophyll content after treatment was analyzed. To perform methyl viologen (MV) treatment, wild type and mutant seedlings were sprayed with 20 μmol·L^-1 MV in 0.1% Tween 20 (V/V). Control plants were sprayed with water and 0.1% Tween 20. The leaf phenotype after treatment was photographed, and the superoxide dismutase (SOD) activity and malondialdehyde (MDA) content were measured. Finally, the expression of starch biosynthesis, chloroplast prenyllipid biosynthesis and chloroplast ABC1 kinase genes in mutants was analyzed using quantitative real-time PCR. 【Result】 Only one transcript, LOC_Os05g25840.3, was detected for the OsABC1K3 gene. The plant height, seed setting rate and seed size of osabc1k3 mutants were reduced compared with wild type. The grain width, grain thickness and 1 000-grain weight were reduced by 13.4%, 6.8% and 18.2%, respectively. However, the grain length was not significantly different from that of wild type. The chlorophyll content of mutant leaves was lower than wild type, while the chlorophyll a/b ratio and carotenoid content were higher. In addition, the mutant chloroplasts were morphologically normal, but lacking starch granules. Photosynthetic activity analysis revealed that the photosynthetic rate of mutants did not differ significantly from that of wild type. After 7 days of HL stress, the mutant leaves etiolated. After 9 days, some of the plants died. The chloroplast thylakoid structure of mutants was disrupted after treatment, presenting extensive vacuolation. Further determination of chlorophyll content revealed that the chlorophyll attenuation of mutants was more severe than wild type. However, the necrosis degree, SOD activity and MDA content of mutant leaves were not significantly different from wild type after MV treatment. Furthermore, OsABC1K3 mutation affected the expression of leaf starch biosynthesis, chloroplast prenyllipid biosynthesis and chloroplast ABC1 kinase genes. 【Conclusion】 OsABC1K3 might participate in HL stress response through genetically controlled signaling pathways, rather than direct oxidative stress defense.

Key words: rice, ABC1, T-DNA insertion mutant, high light stress, starch synthesis