Understanding the mechanism of lipolysis in plants: an opportunity to increase oil yield in crops

Lead Research Organisation: University of Warwick
Department Name: Warwick HRI

Abstract

Oil from seeds forms a major source of nutrition for humans and livestock. It also has many important industrial uses, among them providing an increasingly relevant source of renewable energy (bio-diesel). The rate of oil accumulation in developing seeds is governed predominantly by biosynthesis. However, a number of studies have reported that a significant amount of oil is also turned over during seed development. Blocking this turnover could potentially elevate oil levels by between 5 and 25%, depending on the species and growth conditions. Controlling oil breakdown in seeds requires knowledge of the molecular mechanism, which until recently was completely lacking. This process also occurs after seed germination where it plays a fundamentally important role in providing energy for early seedling growth. I have gained a new insight into the mechanism of oil breakdown by isolating mutants in the model oilseed plant Arabidopsis that are impaired in post-germinative growth. I have discovered that one of these mutants, called sugar-dependent1, has a defect in the enzyme triacylglycerol hydrolase, which catalyses the first step in oil breakdown. The rate of oil breakdown is dramatically slowed in this mutant and as a consequence the developing seeds accumulate significantly more oil. The goals of this proposal are (i) To study how SDP1 is regulated and establish whether oil breakdown can be inhibited during seed development and not following germination. This would allow oil yield to be enhanced with the minimum impact on seedling vigour. (ii) To identify additional structural and regulatory proteins that function with SDP1 to govern the rate of oil breakdown. Disruption of these proteins will be used to block oil breakdown completely and thereby maximize oil accumulation. (iii) To investigate the role of SDP1 in the crop species oilseed rape and determine if oil yield can also be increased by impairing oil turnover. Addressing these objectives will contribute greatly to our fundamental knowledge of the mechanism and regulation of lipolysis, which is major metabolic process that is essential for the life cycle of many plants. The work could also lead to the development of crop plants with a higher oil yield.

Technical Summary

Theoretically, oil accumulation in developing seeds depends on a balance between synthesis and degradation. Several studies suggest that a significant turnover of oil does occur in a variety of oilseed species including the crop oilseed rape. This is evident particularly in the later stages of seed development where there is a fall in oil content. Restricting oil breakdown during seed development might therefore represent a new strategy to enhance oil accumulation and yield in oilseed crops. I have recently discovered the triacylglycerol lipase (SDP1) that is largely responsible for initiating oil breakdown in seeds. Disruption of SDP1 in Arabidopsis impairs oil breakdown following seed germination and therefore slows the rate of early seedling growth. However, it also elevates the level of oil in mature seeds. This supports the hypothesis that there is significant oil turnover during seed development. The first objective of the proposal will be to investigate the regulation of SDP1 and whether oil breakdown can be inhibited during seed development but not following germination. This will be addressed by transforming Arabidopsis with various constructs designed to tag SDP1 in vivo or to control when during development SDP1 is produced. The second objective will be to identify genes that function together with SDP1 to govern oil breakdown, and to disrupt them in order to maximize oil accumulation. These genes will be identified in Arabidopsis using a combination of experimental approaches that utilise mutants I have previously isolated. The third objective of this proposal is to determine if oil yield can also be increased in the crop oilseed rape. This will be investigated using a transgenic approach. SDP1 levels will be suppressed in developing seeds using RNAi and the effect on oil accumulation will be measured.

Publications

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Lessire R (2009) Highlights of recent progress in plant lipid research. in Plant physiology and biochemistry : PPB

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Quettier AL (2009) Storage oil hydrolysis during early seedling growth. in Plant physiology and biochemistry : PPB

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Theodoulou FL (2012) Seed storage oil catabolism: a story of give and take. in Current opinion in plant biology

 
Description Vegetable oils form a major source of nutrition for humans and livestock. They also have many important industrial uses; among them providing a source of renewable energy (bio-diesel). Oil accumulation in developing seeds is governed mainly by synthetic capacity. However, a number of studies have reported that a small but significant amount of oil is being turned over during seed development. Blocking this turnover might elevate oil levels by between 5 and 25%, depending on the species and growth conditions. Controlling oil breakdown in seeds requires knowledge of the biological mechanism, which until recently was lacking. Oil breakdown primarily occurs after seed germination where it plays a fundamental role in providing carbon and energy for early seedling growth. We previously isolated a mutant in the model plant Arabidopsis that allowed us to identify the specific triacylglycerol lipase enzyme called SDP1, which catalyses the first step in oil breakdown. The rate of oil breakdown is dramatically slowed in this mutant and as a consequence the developing seeds accumulate more oil but also have poor seedling growth. The goal of this project was to study how SDP1 is regulated and determine what others lipases account for the residual oil breakdown observed in the mutant, and then to use this knowledge to determine whether oil breakdown can be controlled in the crop oilseed rape to boost oil content in the seeds without impairing the growth of the seedlings. We have established that SDP1 is present in many plant tissues, not just seeds, and that it is regulated in response to energy, stress and growth signals in the cell. Furthermore, we have identified a second lipase called SDP1L that accounts for most of the residual oil breakdown observed in the sdp1 mutant. Finally, we were able to develop a strategy to switch off SDP1 (and SDP1L) specifically during seed development in oilseed rape leading to an 8% increase in seed oil content, without disrupting seedling growth.
Exploitation Route Characterisation of the role of SDP1 in plant oil metabolism has allowed other to use the gene as a tool to study fatty acid and oil synthesis in vegetative tissues.
Sectors Agriculture, Food and Drink,Energy,Manufacturing, including Industrial Biotechology

 
Description Our findings have been used to increase oil content in the seeds of oilseed rape and jatropha and also to greatly increase oil content in the leaves of plants in combination with enhanced rates of fatty acid synthesis. SDP1 therefore provides an underpinning technology for development of food crops and bioenergy crops with enhanced oil content.
First Year Of Impact 2005
Sector Agriculture, Food and Drink,Energy,Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description EUFP7
Amount € 5,790,000 (EUR)
Organisation European Union 
Sector Public
Country European Union (EU)
Start 04/2009 
End 03/2013
 
Description GIN
Amount £1,555,000 (GBP)
Funding ID IF0144 
Organisation Department For Environment, Food And Rural Affairs (DEFRA) 
Sector Public
Country United Kingdom
Start 04/2008 
End 06/2014
 
Description Seeding Catalyst Awards
Amount £10,000 (GBP)
Funding ID BB/SCA/Rothamsted/17 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 11/2017 
End 02/2018
 
Description Industrial collaboration 
Organisation BASF
Country Germany 
Sector Private 
PI Contribution Scientific data, materials and intellectual property.
Collaborator Contribution Scientific data and materials.
Impact Demonstration of a transgenic technology to increase seed oil content and yield in oilseed rape.
Start Year 2007
 
Title Reduced RDM-1 gene expression in plants 
Description Enhanced oil content in plant cells by disrupting expression of triacylglycerol lipase genes related to Arabidopsis SDP1 (aka RDM-1) 
IP Reference US8093452 
Protection Patent granted
Year Protection Granted 2012
Licensed Yes
Impact Disruption of the lipase SDP1 has now been shown my us and by other groups to increase oil content in seeds and leaves of several species of plant.