New Mexico Consortium and Los Alamos National Laboratory, Los Alamos, NM, 87544, USA.
Donald Danforth Plant Science Center, St. Louis, MO, 63132, USA.
Plant J. 2020 Jul;103(2):584-603. doi: 10.1111/tpj.14751. Epub 2020 Apr 20.
One of the major factors limiting biomass productivity in algae is the low thermodynamic efficiency of photosynthesis. The greatest thermodynamic inefficiencies in photosynthesis occur during the conversion of light into chemical energy. At full sunlight the light-harvesting antenna captures photons at a rate nearly 10 times faster than the rate-limiting step in photosynthetic electron transport. Excess captured energy is dissipated by non-productive pathways including the production of reactive oxygen species. Substantial improvements in photosynthetic efficiency have been achieved by reducing the optical cross-section of the light-harvesting antenna by selectively reducing chlorophyll b levels and peripheral light-harvesting complex subunits. Smaller light-harvesting antenna, however, may not exhibit optimal photosynthetic performance in low or fluctuating light environments. We describe a translational control system to dynamically adjust light-harvesting antenna sizes for enhanced photosynthetic performance. By expressing a chlorophyllide a oxygenase (CAO) gene having a 5' mRNA extension encoding a Nab1 translational repressor binding site in a CAO knockout line it was possible to continuously alter chlorophyll b levels and correspondingly light-harvesting antenna sizes by light-activated Nab1 repression of CAO expression as a function of growth light intensity. Significantly, algae having light-regulated antenna sizes had substantially higher photosynthetic rates and two-fold greater biomass productivity than the parental wild-type strains as well as near wild-type ability to carry out state transitions and non-photochemical quenching. These results have broad implications for enhanced algae and plant biomass productivity.
限制藻类生物量生产力的一个主要因素是光合作用的低热力学效率。光合作用中最大的热力学效率低下发生在将光转化为化学能的过程中。在全阳光照射下，捕光天线吸收光子的速度几乎比光合电子传递的限速步骤快 10 倍。多余的捕获能量通过非生产途径耗散，包括产生活性氧物质。通过选择性降低叶绿素 b 水平和外围捕光复合物亚基来减少光捕获天线的光学横截面，可以显著提高光合作用效率。然而，较小的光捕获天线在低光照或波动光照环境下可能无法表现出最佳的光合作用性能。我们描述了一种翻译控制系统，用于动态调整光捕获天线的大小，以提高光合作用性能。通过在 CAO 敲除系中表达具有编码 Nab1 翻译抑制物结合位点的 5' mRNA 延伸的叶绿素脱镁加氧酶（CAO）基因，可以通过 Nab1 对 CAO 表达的光激活抑制来连续改变叶绿素 b 水平，并相应地改变光捕获天线的大小，这是作为生长光强度的函数。重要的是，具有光调节天线大小的藻类具有比亲本野生型菌株高得多的光合作用速率和两倍以上的生物量生产力，以及近乎野生型的进行状态转换和非光化学猝灭的能力。这些结果对提高藻类和植物生物量生产力具有广泛的意义。
