Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), 125 Gwahak-ro, Daejeon 34141, Korea.
Department of Green Chemistry and Environmental Biotechnology, Korea University of Science and Technology (UST), 217 Gajeong-ro, Daejeon 34113, Korea.
Sci Rep. 2016 Sep 16;6:33563. doi: 10.1038/srep33563.
Carotenoids have essential roles in light-harvesting processes and protecting the photosynthetic machinery from photo-oxidative damage. Phytoene synthase (PSY) and Orange (Or) are key plant proteins for carotenoid biosynthesis and accumulation. We previously isolated the sweetpotato (Ipomoea batatas) Or gene (IbOr), which is involved in carotenoid accumulation and salt stress tolerance. The molecular mechanism underlying IbOr regulation of carotenoid accumulation was unknown. Here, we show that IbOr has an essential role in regulating IbPSY stability via its holdase chaperone activity both in vitro and in vivo. This protection results in carotenoid accumulation and abiotic stress tolerance. IbOr transcript levels increase in sweetpotato stem, root, and calli after exposure to heat stress. IbOr is localized in the nucleus and chloroplasts, but interacts with IbPSY only in chloroplasts. After exposure to heat stress, IbOr predominantly localizes in chloroplasts. IbOr overexpression in transgenic sweetpotato and Arabidopsis conferred enhanced tolerance to heat and oxidative stress. These results indicate that IbOr holdase chaperone activity protects IbPSY stability, which leads to carotenoid accumulation, and confers enhanced heat and oxidative stress tolerance in plants. This study provides evidence that IbOr functions as a molecular chaperone, and suggests a novel mechanism regulating carotenoid accumulation and stress tolerance in plants.
类胡萝卜素在光捕获过程中起着重要作用，并能保护光合作用机器免受光氧化损伤。类胡萝卜素生物合成和积累的关键植物蛋白是八氢番茄红素合酶（PSY）和橙（Or）。我们之前分离了参与类胡萝卜素积累和耐盐胁迫的甘薯（Ipomoea batatas）Or 基因（IbOr）。IbOr 调节类胡萝卜素积累的分子机制尚不清楚。在这里，我们表明 IbOr 通过其在体外和体内的热休克蛋白伴侣活性在调节 IbPSY 稳定性方面起着至关重要的作用。这种保护导致类胡萝卜素的积累和非生物胁迫耐受性。热胁迫后，IbOr 在甘薯茎、根和愈伤组织中的转录水平增加。IbOr 定位于细胞核和叶绿体中，但仅在叶绿体中与 IbPSY 相互作用。暴露于热应激后，IbOr 主要定位于叶绿体中。过表达 IbOr 的转基因甘薯和拟南芥增强了对热和氧化应激的耐受性。这些结果表明，IbOr 的热休克蛋白伴侣活性保护 IbPSY 的稳定性，导致类胡萝卜素的积累，并赋予植物增强的耐热和抗氧化应激能力。本研究提供了 IbOr 作为分子伴侣发挥功能的证据，并提出了一种调节植物中类胡萝卜素积累和应激耐受性的新机制。
