7 Plants You’ll Be Seeing More Of As Model Species

You are likely to have come across the famous thale cress, Arabidopsis thaliana if you follow plant science publications. This small weed is from the mustard (Brassicaceae) family and it is quick to grow in greenhouses compared to crop species and easy to use for molecular studies. Arabidopsis is therefore a ‘model’ organism (i.e. can be used as a model for other species) and many discoveries have been previously highlighted on Botany One relating to such as seed germination, nutrient uptake and drought, salt, disease resistance. 

Cesarino and his six colleagues from Brazil, Italy, Germany, Australia, and Saudi Arabia reviewed how plant scientists have benefited from studying model organisms, and introduce new plant species that could be the future model species. 

The researchers write in Annals of Botany, “…[W]e will discuss Marchantia polymorpha as a model to study land plant evolution, Setaria viridis as a model for C4 photosynthesis and biomass recalcitrance, Phragmites australis for invasive plants, Striga hermonthica for plant parasitism, Eutrema salsugineum for salt tolerance, and Cardamine hirsuta for comparative developmental studies.”
Dr Marc Somssich from the University of Melbourne previously written about the history of Arabidopsis and Dr Igor Cesarino from the University of São Paulo has researched Setaria viridis and genes involved in lignification.Dr Raffaele Dello Ioio from the Università di Roma La Sapienza has co-authored a previous publication on how Cardamine hirsuta can be used a model for the evolution of morphological diversity. If you have not come across these species, let me introduce them based on Cesarino and colleagues’ review.

1. Marchantia polymorpha

The common liverwort, Marchantia polymorpha went through a slow molecular evolution, conserving most of their genetic makeup similar to the common ancestor of land plants. As it has a three-month life cycle, it provides an opportunity to study plant evolution relatively quickly. Genome assemblies, transformation protocols have been established in the last decades.

2. Cardamine hirsuta

The hairy bittercress, Cardamine hirsuta is a Arabidopsis look-alike plant but with compound leaves, trichomes, root hairs and exploding pods. It diverged about 14 million years ago from A. thaliana but more developmental mechanisms governing its morphology can be researched using this plant. It has a three to four month life cycle and has a small diploid genome (196 MB). Genome and transcriptome datasets are available and multiple transformation methods have been established for it.

3. Setaria viridis

The green foxtail, Setaria viridis is a common C4 grass, which belongs to the sister tribe of Andropogoneae that includes maize, sorghum and sugarcane. It is the wild ancestor of the cereal crop, foxtail millet and has a life cycle of six to eight weeks. It can be used to research C4 photosynthesis, crop domestication and production of biofuels. Its competition is the model species, Brachypodium distachyon, a C3 grass. Genome assemblies are available and molecular protocols have been produced for it.

4. Eutrema salsugineum

The salt cress, Eutrema salsugineum is a halophytic (salt-tolerant) Arabidopsis look-alike plant. Understanding the mechanisms of its survival of extreme salinity, drought and frost could help breeding more resilient crops. It has a two to three month life cycle and EMS mutagenesis can be done in it. Multiple genome assemblies and transcriptome datasets have been previously reported.

5. Striga hermonthica

The witchweed, Striga hermonthica is a widely distributed parasitic plant that feeds on monocotyledonous plants (e.g. rice, maize, millet, sorghum). The plant can be grown in growth chambers, completing its life cycle in three to four months and it can be attached to the host plant in labs and on agar plates. A reference genome is available and can be transformed by the Agro-drench method.

6. Phragmites australis

The common reed, Phragmites australis is a common perennial grass, which can tolerate many different environments such as salt marshes and arid areas. It has spread from North America across the US and into Canada from the 1800s and can be used to model invasion biology, phenotypic plasticity and testing the “large genome constraint” and  “enemy-release” hypotheses. The reed can be easily propagated through stolons and rhizomes and can reach two meters in height within five months.  Whilst no full genome is available, plastid genome and transcriptome datasets are available, along with transformation protocols.

7. Pisum sativum

Last but not least, the pea, Pisum sativum, has been famous since Mendel but surprisingly little research is focused on peas as it has a large, complicated genome. It is surprising that the pea genome has only been assembled in 2019 but it can now enable scientists to shift from the model legume species Medicago truncatula and Lotus japonica, which are not seed-crop plants. The pea life cycle is eight to twelve weeks long and can be easily grown in the field, glasshouses and growth chambers to study developmental processes (e.g. flowering time control, circadian rhythms) and crop domestication. Over 6,000 accessions are available at the USDA National Plant Germplasm System and several transformations have been published. 

Cesarino and colleagues conclude that “The nineteenth and twentieth centuries were mostly defined by the use of non-model plant models to investigate agriculturally relevant or phenotypically interesting traits” and “With the availability of new ‘omics’ tools, new plant models are added to our collection at an unprecedented speed, and old non-model plant models are, in many regards, elevated to proper model system status”. 

This comprehensive review shows how lesser-known plants could help scientists understand different mechanisms of evolution, stress tolerance, developmental mechanisms and crop domestication. It might also inspire some plant scientists to spice up their Arabidopsis research! 

Follow the authors on Twitter: @KelseyOnScience, @CesarinoIgor, @DelloRaffaele, @itsMikeOgden, @somssichm, @MSomssich