Why we should all (evolutionary biologists) be excited about studying Cannabis.

 

c1

Figure 1. Cannabis plants at the Centennial Seeds facilities.

This is a guest post by Daniela Vergara, a postdoctoral researcher studying the genomic architecture of hybrid species of sunflowers and Cannabis in Nolan Kane’s Lab at the University of Colorado, Boulder.  Daniela also blogs about science at A Ciencia Abierta. Check out her blog for a spanish version of this post.

Cannabis is definitely a cool plant. It has fun names like matanuska thunderfuck, jesus OG or trainwreck and it has been trendy among humans for a very long time (humans have utilized it for thousands of years). Despite this long history, and the fact that Cannabis is the most widely used recreational drug in the world [1], the genomics and the general the biology of these plants have only been partially studied. At the Cannabis Genomic Research Initiative (CGRI) at the University of Colorado Boulder we want to study this genus of plants for several reasons, including: (i) its medical significance, (ii) its importance in the biofuel, fiber, oil, textile and food industries, (iii) its long co-evolutionary relationship with humans as an ancient crop, and (iv) in general, because it is an exciting emerging study system in evolutionary biology.

Why should evolutionary biologists be excited about studying Cannabis?

1. Cannabis plants exhibit amazing phenotypic diversity, especially in the production of secondary metabolites.

Cannabis plants appear to differ in numerous phenotypic aspects.  For example, there is a huge diversity of secondary compounds such as terpenes, which give the plant its smell, and the cannabinoids (the plant produces at least 85 known cannabinoids [2]), which give the plant its medicinal and psychedelic properties. In Cannabis, the production of these secondary metabolites is mostly found in the flower (buds) of the female plant. All plants produce secondary metabolites, which are usually used as chemical defenses against herbivory, pathogens, and abiotic stresses, as well as to mediate symbiotic relationships. However, in many domesticated plants, we have selected against these secondary metabolites [3,4]. In Cannabis the opposite has happened, we have selected for an increase in secondary metabolites. The productions of these metabolites, both the cannabinoids [5,6] and the terpenes [7,8], varies between strains.

Figure 2. Chemical structure of some of the cannabinoids produced by Cannabis plants. Some of the cannabinoids in this picture are the decarboxylated form of the compounds, which occurs upon heating. Taken from Hillig and Mahlberg 2004.

Figure 2. Chemical structure of some of the cannabinoids produced by Cannabis plants. Some of the cannabinoids in this picture are the decarboxylated form of the compounds, which occurs upon heating. Taken from Hillig and Mahlberg (2004).

Furthermore, there are other phenotypic traits that appear to vary between species and strains, such as leaf shape, that have been documented informally (ie. here, here and here). However, there have not been formal scientific studies that quantify these differences. Additionally, there have not been studies that associate genes to any of these important and cool phenotypic characteristics, which is one of the main goals of CGRI. We would like to understand the genetic basis of these phenotypic traits, which give the plant its uniqueness.

 2. We still don’t know exactly how sex and sexual traits are determined in Cannabis.

 Cannabis is typically a dioecious plant, with the production of male (heterogametic sex XY) and female (homogametic sex XX) flowers in different plants [9]. However, some plants are monoecious and produce both male and female flowers.  For a long time, breeders and growers have known that stressing female plants by using, for example, irregular light cycles or adding silver nitrate, causes female plants to start producing male flowers. Some plants may even produce male flowers without being stressed.  Understanding how is sex determined is one of the major outstanding questions in Cannabis biology.  Establishing the determination of sexual traits in Cannabis is, in my opinion, one of the most exciting things offered by this system. In the future, we can expand our research to understand things such as the evolution of sexual chromosomes in plants or sexual antagonism.

 3. We don’t even know how many species of Cannabis there are!

There are many basic questions about the origins and taxonomic classification of this genus, which are both topics of controversy among evolutionary biologists.  For example, we still do not know whether Cannabis is comprised of one or three species (10-12). Or maybe even four?  At the CGRI, we would like to understand first, how much genetic variation there is in the numerous pure C. sativa, C. indica, and C. ruderalis accessions and heirloom varieties. This will lead us to understand the relationships among the major lineages within the genus, the spread of Cannabis throughout the globe, and rates of historical hybridization between the named species.   This line of inquiry will shed light on many interesting topics in evolutionary fields, including gene flow, hybrid speciation and reproductive isolation.

Figure 3. Neighbor-joining tree of four different Cannabis strains, two of them hemp cultivars (USO-31 and Finola) and two of them resin marijuana strains (Purple Kush and Chemdawg). This tree shows the relationship between these four Cannabis accessions, indicating a separation between the hemp and marijuana strains. Taken from van Bakel et al 2011.

Figure 3. Neighbor-joining tree of four different Cannabis strains, two of them hemp cultivars (USO-31 and Finola) and two of them resin marijuana strains (Purple Kush and Chemdawg). This tree shows the relationship between these four Cannabis accessions, indicating a separation between the hemp and marijuana strains. Taken from van Bakel et al (2011).

4. Cannabis has a long, complicated, and interesting history of domestication.

Cannabis offers that unique opportunity to study a plant that has had several events of domestication at different points in time by various cultures. The Chinese used marijuana for medical purposes and for fiber since approximately 2700 BC; the Egyptians used it medically since 1150 BC; the Indians and the Greeks and Romans used for recreation and medical purposes since 2000 BC and 200 BC respectively [13, 14]. Like other domesticated species such as dogs and rice, Cannabis likely has genetic signatures of domestication, in other words, regions in the genome that show signs of selection by humans. Furthermore, Cannabis ruderalis has not been under strong selection because it lacks second metabolite production, which offers a great baseline for genome comparisons. This allows us to determine whether Cannabis genomes vary in different regions suggesting that in the multiple domestication events they were selected for different purposes. For example, we would expect that individuals that have been domesticated for fiber or oil production would have different signatures of selection than those that have been domesticated for second metabolite production.

Figure 4. Female bud with glandular trichomes (clear structures) where most of the secondary metabolites are produced.

Figure 4. Female bud with glandular trichomes (clear structures) where most of the secondary metabolites are produced.

5.  Cannabis has many emerging medical and economical applications.

I hope to have convinced you that Cannabis is not only exciting politically and socially, but is also extremely interesting biologically. I didn’t mention many other cool biological aspects about the plant such as its potentials in treating a variety of diseases: medical marijuana has been used as a pain reliever, in patients with glaucoma, multiple sclerosis, Alzheimer’s disease, depression and breast cancer . Other promising uses include reducing nausea, and either increasing or decreasing appetite, depending on which varieties are used. Hemp, which is a variety of marijuana low in second metabolite production but of high growth, can be used to extract oil and fiber. The products made out of hemp include paper, clothes, body products (lip balm, body lotion, shampoo and conditioner), food products, housing material, biodegradable plastic, isolating material and biofuel.  In the future, at the CGRI we hope to determine the genomic regions in Cannabis related to both the fiber and oil production in hemp and the medical benefits of resin marijuana types, creating useful collaborations between industry and basic research.

Literature Cited:

 1.  UNODC: World Drug Report 2013 United Nations Publication, Sales No. E.11. XI.10.

2. A. T. El-Alfy, K. Ivey, K. Robinson, S. Ahmed, M. Radwan, D. Slade, I. Khan, M. ElSohly, S. Ross. Pharmacology Biochemistry and Behavior 95, 434-442 (2010).

3.  A. Kempel, M. Schaedler, T. Chrobock, M. Fischer, M. van Kleunen. Proceedings of the National Academy of Sciences of the United States of America 108, 5685-5689 (2011).

4.  J. P. Rosenthal, R. Dirzo. Evolutionary Ecology 11, 337-355 (1997).

5.  J. A. Beutler, A. H. Dermarderosian. Economic Botany 32, 387-394 (1978).

6.  K. W. Hillig, P. G. Mahlberg. American Journal of Botany 91, 966-975 (2004).

7.  S. Casano, G. Grassi, V. Martini, M. Michelozzi. Xxviii International Horticultural Congress on Science and Horticulture for People (Ihc2010): A New Look at Medicinal and Aromatic Plants Seminar 925, 115-121 (2011).

8.  K. W. Hillig. Biochemical Systematics and Ecology 32, 875-891 (2004).

9.  V. M. C. Moliterni, L. Cattivelli, P. Ranalli, G. Mandolino. Euphytica 140, 95-106 (2004).

10. K. W. Hillig. Genetic Resources and Crop Evolution 52, 161-180 (2005).

11. H. van Bakel, J. M. Stout, A. G. Cote, C. M. Tallon, A. G. Sharpe, T. R. Hughes, J. E. Page. Genome Biology 12,  (2011).

12. E. P. M. de Meijer, M. Bagatta, A. Carboni, P. Crucitti, V. M. C. Moliterni, P. Ranalli, G. Mandolino. Genetics 163, 335-346 (2003).

13. E. B. Russo. Chemistry & Biodiversity 4, 1614-1648 (2007).

14. H. L. Li. Economic Botany 28, 293-301 (1974).

 

 

7 comments on “Why we should all (evolutionary biologists) be excited about studying Cannabis.

  1. […] overview and history of evolutionary biology. Three more […]

  2. […] Why we should all (evolutionary biologists) be excited about studying Cannabis. […]

  3. […] Why we should all (evolutionary biologists) be excited about studying Cannabis. […]

  4. […] Why we should all (evolutionary biologists) be excited about studying Cannabis. […]

  5. […] Why we should all (evolutionary biologists) be excited about studying Cannabis. […]

Comments are closed.