Dalal Jyoti, Lopez Harry, Vasani Naresh B, Hu Zhaohui, Swift Jennifer E, Yalamanchili Roopa, Dvora Mia, Lin Xiuli, Xie Deyu, Qu Rongda, Sederoff Heike W
Department of Crop Science, North Carolina State University, Campus Box 7287, Raleigh, NC 27695-7287 USA.
Department of Plant and Microbial Biology, North Carolina State University, Campus Box 7612, Raleigh, NC 27695-7612 USA.
Biotechnol Biofuels. 2015 Oct 29;8:175. doi: 10.1186/s13068-015-0357-1. eCollection 2015.
Camelina sativa is an oilseed crop with great potential for biofuel production on marginal land. The seed oil from camelina has been converted to jet fuel and improved fuel efficiency in commercial and military test flights. Hydrogenation-derived renewable diesel from camelina is environmentally superior to that from canola due to lower agricultural inputs, and the seed meal is FDA approved for animal consumption. However, relatively low yield makes its farming less profitable. Our study is aimed at increasing camelina seed yield by reducing carbon loss from photorespiration via a photorespiratory bypass. Genes encoding three enzymes of the Escherichia coli glycolate catabolic pathway were introduced: glycolate dehydrogenase (GDH), glyoxylate carboxyligase (GCL) and tartronic semialdehyde reductase (TSR). These enzymes compete for the photorespiratory substrate, glycolate, convert it to glycerate within the chloroplasts, and reduce photorespiration. As a by-product of the reaction, CO2 is released in the chloroplast, which increases photosynthesis. Camelina plants were transformed with either partial bypass (GDH), or full bypass (GDH, GCL and TSR) genes. Transgenic plants were evaluated for physiological and metabolic traits.
Expressing the photorespiratory bypass genes in camelina reduced photorespiration and increased photosynthesis in both partial and full bypass expressing lines. Expression of partial bypass increased seed yield by 50-57 %, while expression of full bypass increased seed yield by 57-73 %, with no loss in seed quality. The transgenic plants also showed increased vegetative biomass and faster development; they flowered, set seed and reached seed maturity about 1 week earlier than WT. At the transcriptional level, transgenic plants showed differential expression in categories such as respiration, amino acid biosynthesis and fatty acid metabolism. The increased growth of the bypass transgenics compared to WT was only observed in ambient or low CO2 conditions, but not in elevated CO2 conditions.
The photorespiratory bypass is an effective approach to increase photosynthetic productivity in camelina. By reducing photorespiratory losses and increasing photosynthetic CO2 fixation rates, transgenic plants show dramatic increases in seed yield. Because photorespiration causes losses in productivity of most C3 plants, the bypass approach may have significant impact on increasing agricultural productivity for C3 crops.
亚麻荠是一种油料作物，在边际土地上具有巨大的生物燃料生产潜力。亚麻荠种子油已被转化为喷气燃料，并在商业和军事试飞中提高了燃油效率。由于农业投入较低，亚麻荠氢化衍生的可再生柴油在环境方面优于油菜籽衍生的可再生柴油，并且其籽粕已获美国食品药品监督管理局批准可用于动物食用。然而，相对较低的产量使其种植利润较低。我们的研究旨在通过光呼吸支路减少光呼吸造成的碳损失，从而提高亚麻荠种子产量。引入了编码大肠杆菌乙醇酸分解代谢途径中三种酶的基因：乙醇酸脱氢酶（GDH）、乙醛酸羧化酶（GCL）和羟基丙二酸半醛还原酶（TSR）。这些酶竞争光呼吸底物乙醇酸，在叶绿体内将其转化为甘油酸，并减少光呼吸。作为该反应的副产物，二氧化碳在叶绿体内释放，从而增强光合作用。用部分支路（GDH）或完整支路（GDH、GCL和TSR）基因转化亚麻荠植株。对转基因植株的生理和代谢性状进行了评估。
在亚麻荠中表达光呼吸支路基因可降低部分和完整支路表达系的光呼吸并增强光合作用。部分支路的表达使种子产量提高了50 - 57%，而完整支路的表达使种子产量提高了57 - 73%，种子质量没有损失。转基因植株还表现出营养生物量增加和发育加快；它们开花、结籽并比野生型提前约1周达到种子成熟。在转录水平上，转基因植株在呼吸、氨基酸生物合成和脂肪酸代谢等类别中表现出差异表达。与野生型相比，支路转基因植株生长的增加仅在环境或低二氧化碳条件下观察到，而在高二氧化碳条件下未观察到。
光呼吸支路是提高亚麻荠光合生产力的有效途径。通过减少光呼吸损失和提高光合二氧化碳固定率，转基因植株的种子产量显著增加。由于光呼吸会导致大多数C3植物生产力损失，因此支路方法可能对提高C3作物的农业生产力产生重大影响。
