Mussgnug Jan H, Thomas-Hall Skye, Rupprecht Jens, Foo Alexander, Klassen Viktor, McDowall Alasdair, Schenk Peer M, Kruse Olaf, Hankamer Ben
Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld 4072, Australia.
Plant Biotechnol J. 2007 Nov;5(6):802-14. doi: 10.1111/j.1467-7652.2007.00285.x. Epub 2007 Aug 31.
The main function of the photosynthetic process is to capture solar energy and to store it in the form of chemical 'fuels'. Increasingly, the photosynthetic machinery is being used for the production of biofuels such as bio-ethanol, biodiesel and bio-H2. Fuel production efficiency is directly dependent on the solar photon capture and conversion efficiency of the system. Green algae (e.g. Chlamydomonas reinhardtii) have evolved genetic strategies to assemble large light-harvesting antenna complexes (LHC) to maximize light capture under low-light conditions, with the downside that under high solar irradiance, most of the absorbed photons are wasted as fluorescence and heat to protect against photodamage. This limits the production process efficiency of mass culture. We applied RNAi technology to down-regulate the entire LHC gene family simultaneously to reduce energy losses by fluorescence and heat. The mutant Stm3LR3 had significantly reduced levels of LHCI and LHCII mRNAs and proteins while chlorophyll and pigment synthesis was functional. The grana were markedly less tightly stacked, consistent with the role of LHCII. Stm3LR3 also exhibited reduced levels of fluorescence, a higher photosynthetic quantum yield and a reduced sensitivity to photoinhibition, resulting in an increased efficiency of cell cultivation under elevated light conditions. Collectively, these properties offer three advantages in terms of algal bioreactor efficiency under natural high-light levels: (i) reduced fluorescence and LHC-dependent heat losses and thus increased photosynthetic efficiencies under high-light conditions; (ii) improved light penetration properties; and (iii) potentially reduced risk of oxidative photodamage of PSII.
光合作用过程的主要功能是捕获太阳能并以化学“燃料”的形式储存起来。越来越多的光合机制被用于生产生物燃料，如生物乙醇、生物柴油和生物氢气。燃料生产效率直接取决于该系统捕获和转换太阳能光子的效率。绿藻（如莱茵衣藻）已经进化出遗传策略来组装大型光捕获天线复合体（LHC），以便在低光照条件下最大限度地捕获光能，但其缺点是在高太阳辐照度下，大部分吸收的光子会以荧光和热的形式浪费掉，以防止光损伤。这限制了大规模培养的生产过程效率。我们应用RNA干扰技术同时下调整个LHC基因家族，以减少荧光和热造成的能量损失。突变体Stm3LR3的LHCI和LHCII mRNA及蛋白质水平显著降低，而叶绿素和色素合成功能正常。叶绿体基粒的堆叠明显不那么紧密，这与LHCII的作用一致。Stm3LR3还表现出荧光水平降低、光合量子产率提高以及对光抑制的敏感性降低，从而在高光条件下提高了细胞培养效率。总体而言，就自然高光水平下藻类生物反应器的效率而言，这些特性具有三个优势：（i）减少荧光和LHC依赖性热损失，从而在高光条件下提高光合效率；（ii）改善光穿透特性；（iii）潜在降低PSII氧化光损伤的风险。
