Jun Fang, Chenglin Chai, Qian Qian, Chunlai Li, Jiuyou Tang, Lei Sun, Zejun Huang, Xiaoli Guo, Changhui Sun, Min Liu, Yan Zhang, Qingtao Lu, Yiqin Wang, Congming Lu, Bin Han, Fan Chen, Zhukuan Cheng, Chengcai Chu. Mutations of genes in synthesis of the carotenoid precursors of ABA lead to preharvest sprouting and photo-oxidation in rice The Plant Journal (OnlineAccepted Articles). doi:10.1111/j.1365-313X.2008.03411.x

Preharvest sprouting (PHS) or vivipary in cereals is an important agronomic trait that results in significant economic loss. A considerable number of mutations that cause preharvest sprouting have been identified in several species. However, relatively few viviparous mutants in rice have been reported. To explore the PHS mechanism in rice, we carried out an extensive genetic screening and identified 12 pre-harvest spouting (phs) mutants. Based on their phenotypes, these phs mutants were classified into three groups. Here we characterized in detail one group of them, which contains mutations in genes encoding major enzymes of the carotenoid biosynthesis pathway, including phytoene desaturase (OsPDS), ζ-carotene desaturase (OsZDS), carotenoid isomerase (OsCRTISO) and lycopene β-cyclase (β-OsLCY), which are essential for biosynthesis of carotenoid precursors of ABA. As expected, ABA amount was reduced in all four phs mutants compared to that in wild type. Chlorophyll fluorescence analysis revealed the occurrence of photoinhibition in photosystem and decreased capacity in eliminating excess energy by thermal dissipation. The greatly increased activities of reactive oxygen species (ROS) scavenging enzymes and reduced photosystem (PS) II core proteins CP43, CP47 and D1 in leaves of Oscrtiso/phs3-1mutant and OsLCY RNAi transgenic rice indicated that photooxidative damages occurred in PS II, consistent with the accumulation of ROS in these plants. These results suggest that the impairment in carotenoid biosynthesis causes photo-oxidation and ABA-deficiency phenotypes, of which the latter is a major factor controlling the preharvest sprouting trait in rice.

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