Engineering crassulacean acid metabolism to improve water-use efficiency

doi:10.1016/j.tplants.2014.01.006

Trends in Plant Science

Volume 19, Issue 5, May 2014, Pages 327-338

https://doi.org/10.1016/j.tplants.2014.01.006 Get rights and content

Highlights

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CAM species exhibit high WUE.
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Introduction of CAM into crops should enhance WUE and improve carbon balance.
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Genome and transcriptome sequencing of diverse taxa of CAM species is in progress.
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Coexpression network modelling can help define the genetic requirements for CAM biodesign.
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Carboxylation, decarboxylation, and stomatal regulation module engineering will be required.

Climatic extremes threaten agricultural sustainability worldwide. One approach to increase plant water-use efficiency (WUE) is to introduce crassulacean acid metabolism (CAM) into C₃ crops. Such a task requires comprehensive systems-level understanding of the enzymatic and regulatory pathways underpinning this temporal CO₂ pump. Here we review the progress that has been made in achieving this goal. Given that CAM arose through multiple independent evolutionary origins, comparative transcriptomics and genomics of taxonomically diverse CAM species are being used to define the genetic ‘parts list’ required to operate the core CAM functional modules of nocturnal carboxylation, diurnal decarboxylation, and inverse stomatal regulation. Engineered CAM offers the potential to sustain plant productivity for food, feed, fiber, and biofuel production in hotter and drier climates.

Section snippets

Photosynthesis for a parched planet

Earth's population is projected to exceed 9 billion by 2050. The consequent demands on agriculture for food, feed, fiber, and fuels, coupled with decreasing arable land area and increasing nitrogen and phosphate fertilizer requirements for crop production, all point to the need to produce more plant-derived biomass with reduced resource inputs [1]. Approximately 40% of the world's land area is considered arid, semi-arid, or dry sub-humid, with precipitation amounts that are inadequate for most

CAM – a strategic target for synthetic biology

The major plant inorganic CCMs in terrestrial vascular plants are CAM and C₄ photosynthesis [22]. CAM arose through multiple independent evolutionary origins in at least 343 genera across 36 plant families representing >6% of higher plant species [23]. CAM resembles C₄ photosynthesis in its use of C₄ organic acids as storage intermediates during carbon fixation, but exploits a temporal separation of primary and secondary CO₂ fixation. Furthermore, CAM maximizes WUE by concentrating CO₂ around

Engineering of CAM

The development of bioenergy feedstocks and food crops engineered with the improved WUE of CAM plants complements the direct use of CAM species to supply human needs. CAM and C₄ photosynthesis have been described as products of either parallel or convergent evolution of a complex trait with the implication that many, if not all, of the genes and some regulatory elements necessary for these photosynthetic specializations are already present in C₃ species 23, 41, 42, 43. Such reasoning also

Probing phylogenetically diverse lineages to enable comparative CAM genomics

A fundamental requirement for engineered CAM is to first understand the minimal set of genes and proteins required for its efficient establishment and operation. Until recently, there has been a paucity of genome or transcriptome information available for CAM species. However, the genomic sequences and transcriptome atlases available from cycling, facultative, or obligate CAM species sampled from diverse phylogenetic origins should rapidly redefine our understanding of the molecular genetics of

Comparative CAM genomics

Comparative transcriptomic and genomic approaches can be used to discern CAM gene function by comparing the expression patterns of known CAM enzymes and transporters among closely related C₃ and CAM species within the same genus or family that show C₃, weak CAM or strong CAM [23]. Comparative genome and transcriptome sequencing studies of C₃ and C₄ model species from diverse taxonomic origins do not support the duplication or expansion of C₄ pathway genes or the longstanding hypothesis that C₄

Coexpression network modeling of CAM

A key challenge for the engineering of CAM into C₃ plant species lies in understanding the temporal regulatory events controlling not only the core carboxylation–decarboxylation of C₄ acids, but also the coincident metabolic fluxes through glycolysis–gluconeogenesis and storage carbohydrate synthesis and breakdown, as well as stomatal control, over the course of the day–night cycle as illustrated in Figure 3A. A multilayer approach incorporating transcriptional data, functional genomics

Biodesign of CAM modules

Although network-modeling approaches can provide information about new candidate genes by virtue of their association with known genes within a functional module, empirical testing of minimal functional modules, coupled with information from loss-of-function studies of individual enzymes, regulatory proteins, or transcription factors can provide important empirical information about the basic genetic requirements for CAM biodesign. For simplicity, a set of discrete functional modules for

Identifying target host species

Initial CAM biodesign efforts will target the genetic model Arabidopsis, or close relatives, owing to its rapid growth rate and ease of transformation. With regard to bioenergy feedstocks, preferred targets are rapid-cycling C₃ crops such as members of the Brassicaceae, particularly oilseed crops, and fast-growing woody plants within the Populus genus, which are used extensively in the timber, pulp, and paper industries and more recently as a bioenergy crop. There are many genetic and genomic

Moving complex traits into target host species

Many biological processes are controlled by gene modules comprising an array of genes 120, 121. Similarly, complex trait engineering, such as the proposed CAM engineering project outlined here, will require the use of multigene stacking technologies. Most plant genetic engineering attempts have been limited to the introduction of one or a few genes at a time [122]. To address this limitation, new methods have been developed recently to assemble multigene plant transformation vectors that

Concluding remarks and future directions

The ability of succulent CAM species, such as Agave and Opuntia, to maintain high biomass productivities with water input of only 20% of that required by C₃ or C₄ crops has drawn attention to their possible use as feedstocks for biofuel production. Indeed, such CAM species can be grown in areas where precipitation is typically insufficient to support C₃ or C₄ crops. Thus, exploring the agricultural uses of CAM species should bear fruit as global warming continues to erode finite arable land and

Acknowledgments

This Review is based on work supported by the DOE, Office of Science, Genomic Science Program under Award Number DE-SC0008834. The M. crystallinum transcriptome and mRNA expression data were supported by the National Science Foundation, USA (IOS-084373 awarded to K.A.S. and J.C.C.). The K. fedtschenkoi sequencing and CAM functional genomics project was supported by the Biotechnology and Biological Sciences Research Council, UK (BB/F009313/1 awarded to J.H.). This publication was also made

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Trends in Plant Science

ReviewSpecial Issue: Systems BiologyEngineering crassulacean acid metabolism to improve water-use efficiency

Highlights

Section snippets

Photosynthesis for a parched planet

CAM – a strategic target for synthetic biology

Engineering of CAM

Probing phylogenetically diverse lineages to enable comparative CAM genomics

Comparative CAM genomics

Coexpression network modeling of CAM

Biodesign of CAM modules

Identifying target host species

Moving complex traits into target host species

Concluding remarks and future directions

Acknowledgments

Curr. Opin. Chem. Biol.

Curr. Opin. Biotechnol.

J. Plant Physiol.

Plant Sci.

Trends Plant Sci.

Theory Biosci.

Engineering photosynthesis in plants and synthetic microorganisms

J. Exp. Bot.

Global Environment Outlook: Environment for Development

Climate Change 2007: The Physical Science Basis

Widespread crown condition decline, food web disruption, and amplified tree mortalinity with increased climate change-type drought

Proc. Natl. Acad. Sci. U.S.A.

Changes in precipitation with climate change

Clim. Res.

Groundwater depletion and sustainability of irrigation in the US High Plains and Central Valley

Proc. Natl. Acad. Sci. U.S.A.

Water in the balance

Science

Groundwater depletion in the Middle East from GRACE with implications for transboundary water management in the Tigris–Euphrates–Western Iran region

Water Resour. Res.

GRACE, GLDAS and measured groundwater data products show water storage loss in Western Jilin, China

Water Sci. Technol.

Improving photosynthesis

Plant Physiol.

A critical review on the improvement of photosynthetic carbon assimilation in C3 plants using genetic engineering

Crit. Rev. Biotechnol.

The role of tobacco Aquaporin1 in improving water use efficiency, hydraulic conductivity, and yield production under salt stress

Plant Physiol.

The cyanobacterial CCM as a source of genes for improving photosynthetic CO2 fixation in crop species

J. Exp. Bot.

Cyanobacterial-based approaches to improving photosynthesis in plants

J. Exp. Bot.

Design and analysis of synthetic carbon fixation pathways

Proc. Natl. Acad. Sci. U.S.A.

A survey of carbon fixation pathways through a quantitative lens

J. Exp. Bot.

Engineering photorespiration: current state and future possibilities

Plant Biol. (Stuttg.)

The evolution of inorganic carbon concentrating mechanisms in photosynthesis

Philos. Trans. R. Soc. Lond. B: Biol. Sci.

Evolution along the crassulacan acid metabolism continuum

Funct. Plant Biol.

Crassulacean acid metabolism: a curiosity in context

Annu. Rev. Plant Physiol.

Crassulacean acid metabolism: a re-appraisal of physiological plasticity in form and function

Adv. Bot. Res.

A system dynamics model integrating physiology and biochemical regulation predicts extent of crassulacean acid metabolism (CAM) phases

New Phytol.

Metabolite control overrides circadian regulation of phosphoenolpyruvate carboxylase kinase and CO2 fixation in crassulacean acid metabolism

Plant Physiol.

Isolation and characterization of mutants of common ice plant deficient in crassulacean acid metabolism

Plant Physiol.

Crassulacean acid metabolism

CO2-concentrating: consequences in crassulacean acid metabolism

J. Exp. Bot.

Evolutionary and ecological aspects of photosynthetic pathway variation

Annu. Rev. Ecol. Syst.

High productivities of certain agronomic CAM species

Exploiting the potential of plants with crassulacean acid metabolism for bioenergy production on marginal lands

J. Exp. Bot.

The photosynthetic plasticity of crassulacean acid metabolism: an evolutionary innovation for sustainable productivity in a changing world

New Phytol.

Feedstocks for lignocellulosic biofuels

Science

The global potential for Agave as a biofuel feedstock

Review
Special Issue: Systems Biology
Engineering crassulacean acid metabolism to improve water-use efficiency

A critical review on the improvement of photosynthetic carbon assimilation in C₃ plants using genetic engineering

The cyanobacterial CCM as a source of genes for improving photosynthetic CO₂ fixation in crop species

Metabolite control overrides circadian regulation of phosphoenolpyruvate carboxylase kinase and CO₂ fixation in crassulacean acid metabolism

CO₂-concentrating: consequences in crassulacean acid metabolism

Photorespiration and the evolution of C₄ photosynthesis

Evolution of C₄ photosynthesis in the genus Flaveria: how many and which genes does it take to make C₄?