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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

Gas exchange measurements and anatomical features of leaves of bypass transgenics. aA/Cicurves were generated at saturating light (1500 PAR) using the youngest fully expanded leaf. The A/Ci curves were used to calculate Vcmax (maximum rate of RuBiSCO-mediated carboxylation) (c) and Jmax (maximum rate of electron transport) (d) in transgenic and WT leaves. b Apparent rate of CO2 fixation rate (A-value µmol/m2/s) of representative plants from two independent DEF2, DEF2+TG1 and WT lines was measured using LI6400-XT at chamber light levels(~440 PAR). On average, DEF2 transgenics had 20–26 % and DEF2+TG1 plants had 15–28 % increase in photosynthesis over WT plants (n = 4, p < 0.05; error bars standard error). e The leaves on transgenic plants were larger than WT. The twelfth leaf of 7-week-old plants was harvested and approximate leaf area was compared. On average, DEF2 transgenics had about 50 % and DEF2+TG1 plants had about 75 % increase in leaf area over WT plants (n = 4, p < 0.05). f The leaf 12 from representative plants was cleared, and the cross-section was examined for cell distribution. The palisade mesophyll cells and the intercellular spaces were larger the leaves of the bypass leaves (scale bar 0.5 mm)
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Fig3: Gas exchange measurements and anatomical features of leaves of bypass transgenics. aA/Cicurves were generated at saturating light (1500 PAR) using the youngest fully expanded leaf. The A/Ci curves were used to calculate Vcmax (maximum rate of RuBiSCO-mediated carboxylation) (c) and Jmax (maximum rate of electron transport) (d) in transgenic and WT leaves. b Apparent rate of CO2 fixation rate (A-value µmol/m2/s) of representative plants from two independent DEF2, DEF2+TG1 and WT lines was measured using LI6400-XT at chamber light levels(~440 PAR). On average, DEF2 transgenics had 20–26 % and DEF2+TG1 plants had 15–28 % increase in photosynthesis over WT plants (n = 4, p < 0.05; error bars standard error). e The leaves on transgenic plants were larger than WT. The twelfth leaf of 7-week-old plants was harvested and approximate leaf area was compared. On average, DEF2 transgenics had about 50 % and DEF2+TG1 plants had about 75 % increase in leaf area over WT plants (n = 4, p < 0.05). f The leaf 12 from representative plants was cleared, and the cross-section was examined for cell distribution. The palisade mesophyll cells and the intercellular spaces were larger the leaves of the bypass leaves (scale bar 0.5 mm)

Mentions: During photorespiration, glycolate forms glyoxylate which is transaminated to glycine [33], which in turn reacts with folate to form serine (Fig. 1). The amount of glycine and serine in leaves is indicative of the carbon flux through photorespiration [34]; higher ratios of glycine/serine are related to higher RUBP oxygenation [21, 35]. We investigated the glycine/serine ratio in leaves of DEF2 and DEF2+TG1 transgenics. Samples were taken in photorespiratory conditions (high light, about 5 h after dawn; day samples), and non-photorespiratory conditions (1 h before dawn; night samples). In the day samples, glycine/serine ratio was reduced by 23 % in DEF2 and 27 % in DEF2+TG1 plants. There were no differences in glycine/serine ratio between the night time samples. We further investigated whether the bypass-related CO2 evolution in chloroplasts improved plant photosynthesis. CO2 fixation rates (A) were measured in leaves of WT, DEF2 and DEF2+TG1 plants at different intercellular CO2 concentrations (Ci) in high light (1500 PAR) to generate A/Ci curves using LI-6400XT. At low CO2 levels starting from about 100 Ci (ppm), DEF2 and DEF2+TG1 had higher rates of photosynthetic CO2 fixation compared to WT (Fig. 3a). At ambient CO2 and light (~400 ppm, 430 PAR), 4-week-old DEF2 plants showed 20–25 % and DEF2+TG1 plants showed 14–28 % increase in CO2 fixation over WT per unit leaf area (Fig. 3b). The data from A/Ci curves were used to calculate Vcmax (maximum rate of RuBiSCO-mediated carboxylation) and Jmax (maximum rate of electron transport) for multiple WT, DEF2 and DEF2+TG1 plants using the equations by von Caemmerer, Farquhar and Sharkey [36, 37]. In DEF2 line 60 and DEF2+TG1 lines 51 and 69, there was a significant increase in both Vcmax and Jmax (Fig. 3c, d). To determine if the increased photosynthesis was due in part to increased photosynthetic efficiency of photosystem II, we measured the chlorophyll fluorescence in dark-adapted (pre-dawn) plants. The Fv/Fm ratios (Additional file 1: Figure S2) showed no significant change in photosystem efficiency between transgenic plants and WT.Fig. 3


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)

Gas exchange measurements and anatomical features of leaves of bypass transgenics. aA/Cicurves were generated at saturating light (1500 PAR) using the youngest fully expanded leaf. The A/Ci curves were used to calculate Vcmax (maximum rate of RuBiSCO-mediated carboxylation) (c) and Jmax (maximum rate of electron transport) (d) in transgenic and WT leaves. b Apparent rate of CO2 fixation rate (A-value µmol/m2/s) of representative plants from two independent DEF2, DEF2+TG1 and WT lines was measured using LI6400-XT at chamber light levels(~440 PAR). On average, DEF2 transgenics had 20–26 % and DEF2+TG1 plants had 15–28 % increase in photosynthesis over WT plants (n = 4, p < 0.05; error bars standard error). e The leaves on transgenic plants were larger than WT. The twelfth leaf of 7-week-old plants was harvested and approximate leaf area was compared. On average, DEF2 transgenics had about 50 % and DEF2+TG1 plants had about 75 % increase in leaf area over WT plants (n = 4, p < 0.05). f The leaf 12 from representative plants was cleared, and the cross-section was examined for cell distribution. The palisade mesophyll cells and the intercellular spaces were larger the leaves of the bypass leaves (scale bar 0.5 mm)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig3: Gas exchange measurements and anatomical features of leaves of bypass transgenics. aA/Cicurves were generated at saturating light (1500 PAR) using the youngest fully expanded leaf. The A/Ci curves were used to calculate Vcmax (maximum rate of RuBiSCO-mediated carboxylation) (c) and Jmax (maximum rate of electron transport) (d) in transgenic and WT leaves. b Apparent rate of CO2 fixation rate (A-value µmol/m2/s) of representative plants from two independent DEF2, DEF2+TG1 and WT lines was measured using LI6400-XT at chamber light levels(~440 PAR). On average, DEF2 transgenics had 20–26 % and DEF2+TG1 plants had 15–28 % increase in photosynthesis over WT plants (n = 4, p < 0.05; error bars standard error). e The leaves on transgenic plants were larger than WT. The twelfth leaf of 7-week-old plants was harvested and approximate leaf area was compared. On average, DEF2 transgenics had about 50 % and DEF2+TG1 plants had about 75 % increase in leaf area over WT plants (n = 4, p < 0.05). f The leaf 12 from representative plants was cleared, and the cross-section was examined for cell distribution. The palisade mesophyll cells and the intercellular spaces were larger the leaves of the bypass leaves (scale bar 0.5 mm)
Mentions: During photorespiration, glycolate forms glyoxylate which is transaminated to glycine [33], which in turn reacts with folate to form serine (Fig. 1). The amount of glycine and serine in leaves is indicative of the carbon flux through photorespiration [34]; higher ratios of glycine/serine are related to higher RUBP oxygenation [21, 35]. We investigated the glycine/serine ratio in leaves of DEF2 and DEF2+TG1 transgenics. Samples were taken in photorespiratory conditions (high light, about 5 h after dawn; day samples), and non-photorespiratory conditions (1 h before dawn; night samples). In the day samples, glycine/serine ratio was reduced by 23 % in DEF2 and 27 % in DEF2+TG1 plants. There were no differences in glycine/serine ratio between the night time samples. We further investigated whether the bypass-related CO2 evolution in chloroplasts improved plant photosynthesis. CO2 fixation rates (A) were measured in leaves of WT, DEF2 and DEF2+TG1 plants at different intercellular CO2 concentrations (Ci) in high light (1500 PAR) to generate A/Ci curves using LI-6400XT. At low CO2 levels starting from about 100 Ci (ppm), DEF2 and DEF2+TG1 had higher rates of photosynthetic CO2 fixation compared to WT (Fig. 3a). At ambient CO2 and light (~400 ppm, 430 PAR), 4-week-old DEF2 plants showed 20–25 % and DEF2+TG1 plants showed 14–28 % increase in CO2 fixation over WT per unit leaf area (Fig. 3b). The data from A/Ci curves were used to calculate Vcmax (maximum rate of RuBiSCO-mediated carboxylation) and Jmax (maximum rate of electron transport) for multiple WT, DEF2 and DEF2+TG1 plants using the equations by von Caemmerer, Farquhar and Sharkey [36, 37]. In DEF2 line 60 and DEF2+TG1 lines 51 and 69, there was a significant increase in both Vcmax and Jmax (Fig. 3c, d). To determine if the increased photosynthesis was due in part to increased photosynthetic efficiency of photosystem II, we measured the chlorophyll fluorescence in dark-adapted (pre-dawn) plants. The Fv/Fm ratios (Additional file 1: Figure S2) showed no significant change in photosystem efficiency between transgenic plants and WT.Fig. 3

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