Have you ever wondered how plant organs have evolved over the hundreds and millions of years? Land plants evolved from a group of green algae as early as 470 million years ago and all thanks to their evolution, the Earth is beautifully colonized with plants of different species – from algae, to land plants, such as mosses, liverworts and flowering plants, where the latter makes up most of the food on our plate.
However, unlike green algae, land plants developed complex and special organs that have biochemically adapted to withstand environmental changes on land such as high temperature and ultraviolet stresses. These organs can be very different and highly specialized to different groups of plants. For example in the following figure you can see several organs of a moss, a liverwort, and two flowering plants.
Figure extracted from Nature Plants paper “Comparative transcriptomic analysis reveals conserved programmes underpinning organogenesis and reproduction in land plants“
Assistant Professor Marek Mutwil and Dr. Irene Julca from the School of Biological Sciences (SBS) recently published a paper in Nature Plants titled Comparative transcriptomic analysis reveals conserved programmes underpinning organogenesis and reproduction in land plants that shed some light on the evolution of plants’ organs and gametes, also known as reproductive cells.
What piqued the team’s interest to conduct this study on the evolution of land plants’ organs?
There are many existing studies on how the very diverse members of the plant kingdom have evolved. However, the team realized that there is little information about the functions of individual genes, and how these genes contribute to the many different traits (e.g. organs, resistance to desiccation, different metabolites) that plants have evolved. Furthermore, most evolutionary studies are performed by looking only at genomes.
While the genomes can tell you which genes are present in a plant, and whether certain types of genes are more abundant than others, they often cannot tell you which genes are working together or where and when these genes are expressed (well, exceptions are well-studied and conserved genes from model organisms). “Fortunately, there are nowadays lots of gene expression data publicly available, which provided us with the means to study plant evolution from a new angle,” commented Prof. Mutwil, “We felt that the evolution of plant organs is a largest, lowest-hanging fruit and decided to take a closer look.”
First author Dr. Irene Julca, added, “Plants have experienced amazing changes during their evolution, including the development of new organs. Understanding the evolution of such structures and which genes are controlling their functions and features is crucial to know more about how plants adapt to different environments or how to improve our food.”
How was the research conducted?
To conduct the research, the team identified and analyzed hundreds of gene expression profiles for ten land plants, comprising representatives from different clades – bryophytes, lycophytes, gymnosperms, Amborella (a sister to all angiosperms), monocots and eudicots. These clades include both early diverging plants such as mosses, and late diverging plants like rice and wheat. “By performing a comparative analysis of ten plant species, we cover the largest collection of representatives of land plants,” added Dr. Julca.
The data used for this study came from two sources: public databases and the EVOREPRO consortium. While the EVOREPRO consortium aimed to study the evolution of sexual reproduction in plants, Prof. Mutwil and Dr. Julca decided to expand the analysis to include all major organ types in land plants.
The team used all the data collected (transcriptomic and genomic) to conduct the comparative analysis of the different species. These analyses identified which genes are likely important for the formation and function of plant organs (e.g. for making roots) and plant sexual reproduction (e.g. for pollen or egg function).
Plant research does not stop for the dedicated team of researchers during the pandemic as majority of the data analysis was conducted from home and was completed in 1.5 years. Prof. Mutwil commented, “Constant virtual communication is critical to keep the research going especially during the circuit breaker period when lab work was put on hold.”
What are the results gathered from the study and what do they imply?
The outcome of these study are numerous as they:
- Identified hundreds of organ-specific genes that are likely important for the function of the organs.
- Showed that plant organs express similar sets of genes, despite hundreds of million years of evolution.
- Observed that gene expression of male organs and cell types (e.g. pollen, sperm) is more conserved across plants than female organs and cell types (ovules, eggs), suggesting that the male and female reproduction evolves in a fundamentally different way.
- Showed that rather than evolving new genes, land plants tend to repurpose old genes to evolve new organs.
These results highlights that evolution doesn’t only rely on acquiring new genes, but reuses available genetic material.
How do the discoveries in this research impact the future of e.g. other plant research?
“We are the first to do a large-scale comparative transcriptome analysis in the plant kingdom, which opens new opportunities to understand which genes are responsible for the many plant traits (food, medicines, materials) important for humankind, and to understand how plants have evolved,” explained Prof. Mutwil.
“To provide easy access to the data and analyses generated, we have constructed an online database that is publicly available at www.evorepro.plant.tools”, added Dr. Julca. This platform gives researchers all around the globe information about which genes are important for the different organs and allows any user to do custom searches and comparative analysis.
Are there any upcoming research that the team is currently working on?
“Today, Singapore is a City in a Garden, and is one of the greenest cities in the world. We set aside large nature reserves, with about a third of our island covered by trees.”
– Desmond Lee, Minister for National Development (Adapted from https://www.greenplan.gov.sg/key-focus-areas/city-in-nature/)
With Singapore’s emphasis on evolving the country into a City in a Garden, the team looks forward to expanding on this research by including a greater variety of plant species, which will bring about even greater benefits for plant researchers worldwide.