In Control of Transpiration: The Evolutionary Interplay between Cuticle, Stomata, and Air Pores

Lead Research Organisation: University of Cambridge
Department Name: Plant Sciences

Abstract

If you scrape your fingernail lightly across the surface of some plants like the Cactus, you may pick up a smattering of wax, as if you'd run your fingernail down the side of a candle. In fact, almost all the surfaces of plants, the stems, leaves, flowers and fruit are covered in a tiny layer of wax called the cuticle. This layer is too thin to see because it is thousands of times thinner than a human hair. However its effects can be seen. It is this waxy layer that makes leaves look shiny, allows you to polish your apple, and causes water droplets to roll smoothly off the surface of leaves in a rain shower.
It is this waxy cuticle that allows plants to live on the land without drying out. As such, the cuticle is one of the most important evolutionary inventions in the history of our planet because it has allowed life to leave the watery oceans and survive on dry land. Life and land has never been the same since. The cuticle also does a lot of other useful things for the plants. For example, it blocks bacteria and fungi from infecting the plant, much like human skin. Indeed, one of the reasons that fruit can last for days in the fruit bowl without becoming rotten is due to the protective effects of the waxy cuticle.
We have a lot to learn about how plants make waxes, and move these waxes from where they are manufactured inside the plants to the surface of the plant. The waxy components of the cuticle are made, transported and assembled on the surface by proteins, which are encoded for by genes in a plant's DNA. However we have still to identify many of the genes involved in making the cuticle. It is important to identify these genes because it could help us to design better crops to resist diseases and to create fruit that last longer, and have a longer shelf life with less food waste. It may also help us to commercially synthesise waxes by copying these genes into the DNA of other organisms.
Remarkably we also do not know how plants first evolved the wax cuticle. We do not know what the function of the waxy layer was in the first land plants, what steps were involved in the evolution of the waxy layer, and how it affected the biology of these land plants. We don't know which genes were important in its evolution or how the cuticle has changed and evolved over millions of years. However, by studying the cuticle in plants that represent the first lineages to survive on land, we can get a sense of how the cuticle has changed through evolution and with changing climate.
In this project I would look at living relatives of some of the earliest plants to move onto land. I will compare the DNA of plants that never moved onto land and do not have a cuticle, with DNA from land plants that do have a cuticle. This will help detect genes that are involved in making the cuticle and reveal how these genes have changed over time. I will interfere with these genes to stop them working, in order to see how they make the waxy cuticle in these early plants. Together this will help us to better understand to what extent all land plants have the same genes to make cuticle in the same way, and to what extent the cuticle had similar properties and functions in the past and present.
Plants are constantly absorbing water from the soil and transferring it to the atmosphere via tiny pores called stomata - a process called transpiration. Together plants all over the planet release an enormous amount of moisture into the air, which in turn forms clouds and rain. The waterproof cuticle drastically reduces transpiration and consequently affects the global climate. We do not know how the cuticle of plants will respond to man made changes to the climate. This study will lead to better understanding of the cuticle across all land plants and allow us to predict the effect of changing temperature, carbon dioxide, and drought on the cuticle. This in turn will allow us to better understand how plants will respond to the changing climate

Planned Impact

Climate Change Science. Our rapidly changing global climate impacts on plant traits such as stomata, which can then feedback on global processes including transpiration. It is an important applied research to evaluate and predict how plants will respond to changing environments and climate. These predictions may indicate when and where plants may mitigate or exacerbate the effects of climate change. Such predictions depend in part on a thorough understanding of plant physiology, and how plant processes will respond to environmental stimulus. In this regard it is far from clear to what extent the cuticle or cuticle-stomatal interactions respond to changing environment and this is a significant gap in our knowledge that may affect predictive power. This proposed research will give some insight into these uncertainties and allow better predictions about plant responses in a changing world.

Agriculture and Food Security. The cuticle performs many important roles in crop plants. These functions include: 1) acting as physical barrier to pathogen attack and a source of signals in plant-pathogen interactions; 2) maintaining the integrity, appearance, and shelf life of fruit, and; 3) determining the degree of water loss from crop plants, in conjunction with stomatal pores. The cuticle is an important but under-utilised target for crop improvement and marker assisted breeding, and offers a important target for crop improvement particularly for arid agricultural land. An example of a crop that has been improved by breeding of a cuticle trait is the naked hulled variety of barley, used for human consumption as it is easily threshed. The easily removed barley hull in this variety is due to an allelic mutant of the SHN gene family that controls cuticle formation and hull adhesion in the barley seed. The research proposed here will reveal the conservation and diversification of genetic pathways regulating cuticle formation, and highlight important targets within genetic 'toolkit' that may be manipulated to improve crop plants. Modifications to cuticle on fruits for example could lead to better fruit preservation, longer shelf life, and less food waste. Better understanding of cuticle-stomatal interactions will help understand potential trade-offs associated with cuticle modification.

Biofuels Industry. Waxes, such as occur in plant cuticle, are high-value, high-energy products that are used in a variety of industrial and commercial applications e.g jojoba wax esters. Most commercial waxes are produced by chemical synthesis, fossil fuel extraction, and from a small number of plant and animal species. The diversity and yield of these waxes is low. Improved understanding of plant wax biosynthesis will allow genetic engineering of wax synthesis in higher yielding oil-rich seed crops, such as oil seed rape, on in lipid-rich algal species. Such approaches would produce higher yields and improved commercialization of waxes and generate a greater range of different waxes with different properties. The value and the range of applications of biofuels would be greatly increased. This proposal would generate abundant data regarding the conservation of was biosynthesis components across land plants and algae and highlight genomic diversity in these genetic components that would be useful in synthesizing a range of wax products in diverse organisms.

Public Interest and Students. This research touches on several areas of research that are of topical interest to the public: agriculture, food security, biofuels and climate change. The data and publications from this research will therefore enhance and inform public debate. Such practical concerns are also engaging points of discussion and provide useful foci for high school and undergraduate teaching.

Publications

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Cheng S (2018) 10KP: A phylodiverse genome sequencing plan. in GigaScience

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Ellis AG (2014) Floral trait variation and integration as a function of sexual deception in Gorteria diffusa. in Philosophical transactions of the Royal Society of London. Series B, Biological sciences

 
Description ll land plants are pigmented by flavonoids and their anthocyanin derivatives, with one exception. In the order Caryophyllales, which contains the colourful beetroot, anthocyanins have been replaced with a pigment type called Betalains. Collaborative research between the Brockington Lab and colleagues at the University of Michigan, and Oberlin College, USA has revealed the genetic origins of the betalain pathway. The research demonstrates that lineage-specific radiations of cytochrome P450 and 4,5-dioxygenase genes within the Caryophyllales simultaneously gave rise to new enzymatic isoforms associated with betalain synthesis. The novel isoforms likely evolved new substrate specificities that allowed them to synthesise betalains from tyrosine precursors. These discoveries open a range of possibilities with respect to the genetic engineering of betalain pigmentation. The work is published in two linked papers in Molecular Biology and Evolution and the New Phytologist, and was funded by NERC and the National Science Foundation. We have since discovered the identify of a key previously unknown enzymatic isoform of Arogenate De-hydrogenase which is responsible for the emergence of tryosine-enriched metabolisms in Caryophylalles. We have also shown that betalain pigmentation has evolved multiple times within Caryophyllales. With respect to cuticle evolution we have discovered that there are two isoforms of a cuticle related enzyme. We believe that one. of the isoforms is representative of an earlier pre-adaptation state and are testing this hypothesis to see if we can identify what changes occurred in this protein to enable cuticle evolution. We think this finding will be a major leverage in understanding the evolution of the cuticle. With respect to the garden network we have shown that gardens do an exceptional job of conserving plant diversity world-wide but have key objectives still to fulfil with respect to ex-situ conservation.
Exploitation Route lots of applied aspects to this - mainly there production of betalains, betalain intermediates, and tyrosine derived pharmaceuticals
Sectors Communities and Social Services/Policy,Environment,Leisure Activities, including Sports, Recreation and Tourism,Pharmaceuticals and Medical Biotechnology

 
Description Our data from our Nature Plants paper has been used to improve the quality of the Plant Search database that allows our garden network to monitor the conservation value of botanic gardens world-wide. We have implemented a 10 year living collection strategy in the Cambridge University Botanic Gardens, which is built on the findings of our Nature Plants paper.
Sector Environment
Impact Types Societal,Policy & public services

 
Description BBSRC High Value Chemicals from Plants Award
Amount £29,230 (GBP)
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 01/2016 
End 01/2017
 
Description BBSRC iCASE PHD Studentship
Amount £120,000 (GBP)
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 10/2017 
End 10/2021
 
Description NSF Department of Environmental Biology
Amount $45,000 (USD)
Funding ID DEB-1354048 
Organisation National Science Foundation (NSF) 
Sector Public
Country United States
Start 03/2014 
End 03/2017
 
Title A database of all unique plants grown in the word's botanic gardens 
Description We analysed the redundancy of all collections data from 1/3 of the worlds botanic gardens, and produced a unique list of all plants currently cultivated ex-situ as a measure of the conservation capacity of botanic gardens globally. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact It allowed analysis of the performance of botanic gardens with respect to conservation, and allows gardens to search the contents of other gardens. 
URL https://www.bgci.org/plant_search.php
 
Title Asymmetric Gene Radiation Detection 
Description The technique is an important pipeline in identifying gene radiations that are unique to selected lineages of land plants, and which may harbour adaptive genes. 
Type Of Material Data analysis technique 
Provided To Others? No  
Impact I delivered a successful job talk based on this technique and was subsequently appointed as a permanent lecturer at the Department of Plant Sciences, Cambridge 
 
Description Morphological analysis of the cuticle in Marchantia 
Organisation National Museum of Natural History
Country United States 
Sector Academic/University 
PI Contribution Provision of material, and analyses, and research time towards a scanning electron microscopy
Collaborator Contribution Provision of expertise, material and microscopes for analyses of our material
Impact A substantial data set, including many thousands of images which are currently being prepared for publication.
Start Year 2013
 
Description BBC Interview: "Flowering of the Titan Arum" 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact A conducted an interview with the BBC on the rare flowering of the Titan Arum at the Cambridge University Botanic Gardens, the interview was broadcast on local radio and the reported on the main BBC website.
Year(s) Of Engagement Activity 2015
URL http://www.bbc.co.uk/news/uk-england-cambridgeshire-33611757
 
Description Exhibit at the Festival of Plants 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact about 1500 people attended festival of plants, and we communicated directly to a few hundred, numbers at the festival are increasing indicating positive impact
Year(s) Of Engagement Activity 2016
 
Description Magazine Article: "Exposing our Hidden Collections" 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact A wrote a centre-spread article in the Botanic Gardens Newsletter on the botanical heritage collections present in the University of Cambridge
Year(s) Of Engagement Activity 2016
 
Description Magazine Article: "From Japan, with Love" 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact I wrote a brief article on the impact and implications of the Nagoya Protocol for Plant Sciences
Year(s) Of Engagement Activity 2016
 
Description Media outreach associated with publication on contents of world's botanic gardens 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Our paper published in Nature Plants "Ex-situ conservation of plant diversity in the world's botanic gardens" was covered by 31 news stores in 26 media outlets, was tweeted over 200 times, and recommended on F1000
Year(s) Of Engagement Activity 2017
URL https://www.bgci.org/news-and-events/news/1428/
 
Description Public Lecture: "Tour of the Systematic Beds" 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact The tour of the systematics beds was given as part of a Bioblitz event held at the Cambridge University Botanic Gardens, and involved guiding about 20 people around a heritage part of the garden and teaching them about plant conservation.
Year(s) Of Engagement Activity 2016
URL http://www.cambridge-news.co.uk/Discover-weird-wonderful-wildlife-Cambridge/story-26674017-detail/st...
 
Description Public Lecture: "Extreme Green: Plant Adaptations to the Worlds Harshest Environments" 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact A public lecture delivered as part of a drop in Science on Sundays programme, with about 15-20 in the audience, good questions and good feedback on the forms.
Year(s) Of Engagement Activity 2015
URL http://www.cambplants.group.cam.ac.uk/news-and-events/events/science-on-sundays-extreme-green-explor...
 
Description Public Lecture: "What shall we take with us in the ark" 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact The talk on the importance of plant conservation was delivered as part of a "Fascination with Plants" day, and was attended by about 20 people - it was well received and stimulated many questions and good debate.
Year(s) Of Engagement Activity 2015
 
Description Sat on a strategic review panel looking at the 10year research plan for Xishuangbanna Botanic Garden, China 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Policymakers/politicians
Results and Impact The purpose of this activity was to help a leading Chinese Botanical Institution to develop a long term strategy to support plant diversity research. One of the outcomes and reccomndation was a focus on early diverging land plants, which is the subject of my NERC award.
Year(s) Of Engagement Activity 2019
URL http://xtbgsymposium2019.csp.escience.cn/dct/page/1
 
Description Schools Lecture: "How do Botanic Gardens Work" 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact 15 high school students from the Cambridge University Technical College attended the lecture during a visit to the botanic gardens, and found the talk stimulating, with many questions and good discussion. Feedback from their teacher and students was good.
Year(s) Of Engagement Activity 2015
 
Description Talk given at the Festival of Plants 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Talk lead to several minutes of discussion and questions.
Many individuals delivered positive feed-back

After my talk many people visited out permanent festival stand for further engagement
Year(s) Of Engagement Activity 2014
URL http://www.botanic.cam.ac.uk/Botanic/Event.aspx?prcid=0&ix=351&ppid=0&pid=0