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A photorespiratory bypass increases plant growth and seed yield in biofuel crop Camelina sativa.

Dalal J, Lopez H, Vasani NB, Hu Z, Swift JE, Yalamanchili R, Dvora M, Lin X, Xie D, Qu R, Sederoff HW - Biotechnol Biofuels (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Crop Science, North Carolina State University, Campus Box 7287, Raleigh, NC 27695-7287 USA.

ABSTRACT

Background: 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.

Results: 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.

Conclusions: 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.

No MeSH data available.


Related in: MedlinePlus

Phenotypes of bypass transgenics when grown in elevated or reduced CO2 environment. a In elevated CO2 conditions (1500 ppm), bypass plants have no detectable growth advantage over WT plants. b, c At 5 weeks of age, bypass transgenics grown in high CO2 showed no significant height or leaf number advantage over WT (dark red bars). This is in contrast with the significant advantage (marked by asterisk) in height and leaf number observed in bypass transgenics in ambient CO2 conditions (light gray bars). d When plants are grown in ambient CO2 and exposed to low CO2 conditions (100 ppm) for 5 h, WT show a shriveling response, which is not shown by the bypass transgenics. 10 ≤ n ≤ 12, error bars standard error
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Fig8: Phenotypes of bypass transgenics when grown in elevated or reduced CO2 environment. a In elevated CO2 conditions (1500 ppm), bypass plants have no detectable growth advantage over WT plants. b, c At 5 weeks of age, bypass transgenics grown in high CO2 showed no significant height or leaf number advantage over WT (dark red bars). This is in contrast with the significant advantage (marked by asterisk) in height and leaf number observed in bypass transgenics in ambient CO2 conditions (light gray bars). d When plants are grown in ambient CO2 and exposed to low CO2 conditions (100 ppm) for 5 h, WT show a shriveling response, which is not shown by the bypass transgenics. 10 ≤ n ≤ 12, error bars standard error

Mentions: To test if the increase in growth in the transgenic plants was due to higher CO2 use efficiency, we measured the growth of bypass expressing plants under ambient CO2, high CO2 and low CO2 conditions. At 5 weeks of age, when grown in ambient CO2 conditions, transgenic plants were about 4–7 cm taller than WT plants, but at elevated CO2 (1500 ppm), the heights of the transgenic plants were similar to WT (Fig. 8a, b). Similarly, in ambient CO2 conditions, bypass plants had 5–7 leaves more than WT, but at elevated CO2 conditions, there was no significant difference in the leaf numbers (Fig. 8c). We further tested if there was an effect of low CO2 on the growth of transgenics. When the plants were grown for 5 weeks in ambient CO2 and then moved to low CO2 conditions (~100 ppm) for 5 h, we observed a dramatic phenotypic difference between transgenic and WT plants. Under this treatment, the WT plants became wilted, whereas the DEF2 and DEF2+TG1 plants remained turgid (Fig. 8d). Upon restoration of ambient CO2 conditions, WT plants reverted back to a turgid phenotype. These data indicate that CO2 supply may have improved in bypass transgenic plants.Fig. 8


A photorespiratory bypass increases plant growth and seed yield in biofuel crop Camelina sativa.

Dalal J, Lopez H, Vasani NB, Hu Z, Swift JE, Yalamanchili R, Dvora M, Lin X, Xie D, Qu R, Sederoff HW - Biotechnol Biofuels (2015)

Phenotypes of bypass transgenics when grown in elevated or reduced CO2 environment. a In elevated CO2 conditions (1500 ppm), bypass plants have no detectable growth advantage over WT plants. b, c At 5 weeks of age, bypass transgenics grown in high CO2 showed no significant height or leaf number advantage over WT (dark red bars). This is in contrast with the significant advantage (marked by asterisk) in height and leaf number observed in bypass transgenics in ambient CO2 conditions (light gray bars). d When plants are grown in ambient CO2 and exposed to low CO2 conditions (100 ppm) for 5 h, WT show a shriveling response, which is not shown by the bypass transgenics. 10 ≤ n ≤ 12, error bars standard error
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4625952&req=5

Fig8: Phenotypes of bypass transgenics when grown in elevated or reduced CO2 environment. a In elevated CO2 conditions (1500 ppm), bypass plants have no detectable growth advantage over WT plants. b, c At 5 weeks of age, bypass transgenics grown in high CO2 showed no significant height or leaf number advantage over WT (dark red bars). This is in contrast with the significant advantage (marked by asterisk) in height and leaf number observed in bypass transgenics in ambient CO2 conditions (light gray bars). d When plants are grown in ambient CO2 and exposed to low CO2 conditions (100 ppm) for 5 h, WT show a shriveling response, which is not shown by the bypass transgenics. 10 ≤ n ≤ 12, error bars standard error
Mentions: To test if the increase in growth in the transgenic plants was due to higher CO2 use efficiency, we measured the growth of bypass expressing plants under ambient CO2, high CO2 and low CO2 conditions. At 5 weeks of age, when grown in ambient CO2 conditions, transgenic plants were about 4–7 cm taller than WT plants, but at elevated CO2 (1500 ppm), the heights of the transgenic plants were similar to WT (Fig. 8a, b). Similarly, in ambient CO2 conditions, bypass plants had 5–7 leaves more than WT, but at elevated CO2 conditions, there was no significant difference in the leaf numbers (Fig. 8c). We further tested if there was an effect of low CO2 on the growth of transgenics. When the plants were grown for 5 weeks in ambient CO2 and then moved to low CO2 conditions (~100 ppm) for 5 h, we observed a dramatic phenotypic difference between transgenic and WT plants. Under this treatment, the WT plants became wilted, whereas the DEF2 and DEF2+TG1 plants remained turgid (Fig. 8d). Upon restoration of ambient CO2 conditions, WT plants reverted back to a turgid phenotype. These data indicate that CO2 supply may have improved in bypass transgenic plants.Fig. 8

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Crop Science, North Carolina State University, Campus Box 7287, Raleigh, NC 27695-7287 USA.

ABSTRACT

Background: 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.

Results: 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.

Conclusions: 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.

No MeSH data available.


Related in: MedlinePlus