Department of Horticultural Science, North Carolina State University, Box 7609, Raleigh, NC 27695, USA.
Biotechnol Prog. 2011 Mar-Apr;27(2):351-9. doi: 10.1002/btpr.573. Epub 2011 Mar 1.
Sweet potato is a major crop in the southeastern United States, which requires few inputs and grows well on marginal land. It accumulates large quantities of starch in the storage roots and has been shown to give comparable or superior ethanol yields to corn per cultivated acre in the southeast. Starch conversion to fermentable sugars (i.e., for ethanol production) is carried out at high temperatures and requires the action of thermostable and thermoactive amylolytic enzymes. These enzymes are added to the starch mixture impacting overall process economics. To address this shortcoming, the gene encoding a hyperthermophilic α-amylase from Thermotoga maritima was cloned and expressed in transgenic sweet potato, generated by Agrobacterium tumefaciens-mediated transformation, to create a plant with the ability to self-process starch. No significant enzyme activity could be detected below 40°C, but starch in the transgenic sweet potato storage roots was readily hydrolyzed at 80°C. The transgene did not affect normal storage root formation. The results presented here demonstrate that engineering plants with hyperthermophilic glycoside hydrolases can facilitate cost effective starch conversion to fermentable sugars. Furthermore, the use of sweet potato as an alternative near-term energy crop should be considered.
甘薯是美国东南部的主要作物，它所需的投入很少，在边际土地上生长良好。它在贮藏根中积累大量的淀粉，并且已被证明在东南部，每英亩种植面积的乙醇产量与玉米相当或优于玉米。淀粉转化为可发酵糖（即用于乙醇生产）是在高温下进行的，需要热稳定和热活性的淀粉分解酶的作用。这些酶被添加到淀粉混合物中，影响整体工艺经济性。为了解决这一缺点，从海洋栖热菌（Thermotoga maritima）中克隆并在转基因甘薯中表达了编码一种嗜热α-淀粉酶的基因，通过根癌农杆菌介导的转化生成，从而创造了一种具有自我加工淀粉能力的植物。在 40°C 以下检测不到明显的酶活性，但在转基因甘薯贮藏根中的淀粉很容易在 80°C 下水解。该转基因对正常贮藏根的形成没有影响。这里呈现的结果表明，用嗜热糖苷水解酶工程化植物可以促进成本效益高的淀粉转化为可发酵糖。此外，应考虑将甘薯用作替代的近期能源作物。
