Photorespiration is required in C3 plants to metabolize toxic glycolate formed when ribulose-1,5-bisphosphate carboxylase-oxygenase oxygenates rather than carboxylates ribulose-1,5-bisphosphate. Depending on growing temperatures, photorespiration can reduce yields by 20 to 50% in C3 crops. Inspired by earlier work, we installed into tobacco chloroplasts synthetic glycolate metabolic pathways that are thought to be more efficient than the native pathway. Flux through the synthetic pathways was maximized by inhibiting glycolate export from the chloroplast. The synthetic pathways tested improved photosynthetic quantum yield by 20%. Numerous homozygous transgenic lines increased biomass productivity by >40% in replicated field trials. These results show that engineering alternative glycolate metabolic pathways into crop chloroplasts while inhibiting glycolate export into the native pathway can drive increases in C3 crop yield under agricultural field conditions.

Synthetic glycolate metabolism pathways stimulate crop growth and productivity in the field

A number of recent studies have provided strong support demonstrating that improving the photosynthetic processes through genetic engineering can provide an avenue to improve yield potential. The major focus of this review is on improvement of the Calvin–Benson cycle and electron transport. Consideration is also given to how altering regulatory process may provide an additional route to increase photosynthetic efficiency. Here we summarize some of the recent successes that have been observed through genetic manipulation of photosynthesis, showing that, in both the glasshouse and the field, yield can be increased by >40%. These results provide a clear demonstration of the potential for increasing yield through improvements in photosynthesis. In the final section, we consider the need to stack improvement in photosynthetic traits with traits that target the yield gap in order to provide robust germplasm for different crops across the globe.

Feeding the world: improving photosynthetic efficiency for sustainable crop production

Camelina uses, genetics, genomics, production, and management

Global food security depends on three main cereal crops (wheat, rice and maize) achieving and maintaining high yields, as well as increasing their future yields. Fundamental to the production of this biomass is photosynthesis. The process of photosynthesis involves a large number of proteins that together account for the majority of the nitrogen in leaves. As large amounts of nitrogen are removed in the harvested grain, this needs to be replaced either from synthetic fertilizer or biological nitrogen fixation. Knowledge about photosynthetic properties of leaves in natural ecosystems is also important, particularly when we consider the potential impacts of climate change. While the relationship between nitrogen and photosynthetic capacity of a leaf differs between species, leaf nitrogen content provides a useful way to incorporate photosynthesis into models of ecosystems and the terrestrial biosphere. This review provides a generalized nitrogen budget for a C3 leaf cell and discusses the potential for improving photosynthesis from a nitrogen perspective.

/pdf/the-nitrogen-cost-of-photosynthesis-vt7jk3y5so.pdf

The nitrogen cost of photosynthesis.

In this article, we have altered the levels of three different enzymes involved in the Calvin-Benson cycle and photorespiratory pathway. We have generated transgenic Arabidopsis plants with altered combinations of sedoheptulose 1,7-bisphosphatase (SBPase), fructose 1,6-bisphophate aldolase (FBPA) and the glycine decarboxylase-H protein (GDC-H) gene identified as targets to improve photosynthesis based on previous studies. Here, we show that increasing the levels of the three corresponding proteins, either independently or in combination, significantly increases the quantum efficiency of PSII. Furthermore, photosynthetic measurements demonstrated an increase in the maximum efficiency of CO2 fixation in lines over-expressing SBPase and FBPA. Moreover, the co-expression of GDC-H with SBPase and FBPA resulted in a cumulative positive impact on leaf area and biomass. Finally, further analysis of transgenic lines revealed a cumulative increase of seed yield in SFH lines grown in high light. These results demonstrate the potential of multigene stacking for improving the productivity of food and energy crops.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/pbi.12676

Simultaneous stimulation of sedoheptulose 1,7‐bisphosphatase, fructose 1,6‐bisphophate aldolase and the photorespiratory glycine decarboxylase‐H protein increases CO2 assimilation, vegetative biomass and seed yield in Arabidopsis

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.

/pdf/a-photorespiratory-bypass-increases-plant-growth-and-seed-5du7qy8tfd.pdf

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

Summary Adding semitransparent organic solar cells (ST-OSCs) to a greenhouse structure enables simultaneous plant cultivation and electricity generation, thereby reducing the greenhouse energy demand. However, there is a need to establish the impact of such systems on plant growth and indoor climate and to optimize system tradeoffs. In this work, we consider plant growth under OSCs and system-relevant design. We evaluate the growth of red leaf lettuce under ST-OSC filters and compare the impact of three different OSC active layers that have unique transmittance. We find no significant differences in the fresh weight and chlorophyll content of the lettuce grown under these OSC filters. In addition, OSCs provide an opportunity for further light and thermal management of the greenhouse through device design and optical coatings. The OSCs can thus affect plant growth, power generation, and thermal load of the greenhouse, and this design trade space is reviewed and exemplified.

Balancing crop production and energy harvesting in organic solar-powered greenhouses

Semi-transparent Organic Solar Cells for Greenhouse Application

Yuan Xiong1*, Eshwar Ravishankar2, Jennifer Swift3, Harald Ade1*, Ronald Booth2, Melodi Charles4, Reece Henry1, Brendan O’Connor2, Jeromy James Rech5, Carole Saravitz3, Heike Sederoff4, Long Ye1, Wei You5
1. Department of Physics, Organic and Carbon Electronics Lab (ORaCEL), North Carolina State University, Raleigh, NC 27695, USA
2. Department of Mechanical and Aerospace Engineering and ORaCEL, North Carolina State University, Raleigh, NC 27695, USA 
3. Department of Plant Biology, North Carolina State University, Raleigh, NC 27695, USA
4. Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC 27695, USA 
5. Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
E-mail: yxiong8@ncsu.edu; hwade@ncsu.edu

 Semitransparent organic solar cells (ST-OSCs) show great potential in building-integrated photovoltaics due to the advantages in solution processability, flexibility, and transparency. Herein, we present a systematic study on the application of high-performance ST-OSC filters in a greenhouse by utilizing three representative systems with different spectral responses, namely, FTAZ:PC71BM[1], FTAZ:IT-M[2, 3], and PTB7-Th:IEICO-4F[4]. Specifically, the cultivation of red leaf lettuce is conducted in a controlled environment growth chamber, which is possible to duplicate any climate, and under different ST-OSC filters. In principle, the ST-OSCs absorb a portion of the solar spectrum for power generation and lettuce utilizes the penetrated light for photosynthesis. Furthermore, we quantitatively investigate the leaf area and number profiles, plant biomass, and photosynthetic rate under the as-prepared ST-OSC filters treatments. On the base of statistical analysis after the growth cycle, we can identify the best ST-OSC for plant growth. These results thus pave the way to integrate ST-OSCs with greenhouses. 

[1]	S. C. Price, A. C. Stuart, L. Yang, H. Zhou, W. You, Journal of the American Chemical Society 2011, 133, 4625.
[2]	L. Ye, Y. Xiong, Q. Zhang, S. Li, C. Wang, Z. Jiang, J. Hou, W. You, H. Ade, Advanced Materials 2018, 30, 1705485.
[3]	Y. Xiong, L. Ye, A. Gadisa, Q. Zhang, J. J. Rech, W. You, H. Ade, Advanced Functional Materials 2019, 29, 1806262.
[4]	X. Song, N. Gasparini, L. Ye, H. Yao, J. Hou, H. Ade, D. Baran, ACS Energy Letters 2018, 3, 669.

Jennifer Swift

Papers

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

Balancing crop production and energy harvesting in organic solar-powered greenhouses

Semi-transparent organic solar cells for greenhouse application (Conference Presentation)