Annelie Carlsbecker: “Plants must be prepared for just about anything”
When it comes to growth and flexibility, the plant kingdom exceeds us humans by far. Annelie Carlsbecker keeps finding new signs of the intricate interplay and adaptability of plants. “The fascinating part is that not only do plant cells have the ability to exchange information, they also know what information they need to share in order to develop properly. And how do they know that?”
At Campus Ultuna, visitors are greeted by Uppsala BioCenter’s bright yellow entrance. BioCenter is home to one of the smaller research programmes at Uppsala University: Physiological Botany. The department belongs to the Department of Organismal Biology at the Evolutionary Biology Centre, EBC, but is also part of the Linnean Centre for Plant Biology, which is a joint centre of excellence between Uppsala University and the Swedish University of Agricultural Sciences.
Annelie Carlsbecker meets us in the foyer and guides us to her office, nested among those of her fellow plant researchers at SLU.
“Our research program is small, so it benefits us enormously to be around so many people with such great expertise. Here you’ll find researchers who master all kinds of methods, ranging from genetics and different types of microscopy to advanced molecular biological methods and bioinformatics. On the other hand, EBC is where we teach at and have joint seminars with others at our department. So both campuses are our natural habitats.”
The research group studies the development of plants on a genetic and molecular level. The group makes use of the model plant thale cress, Arabidopsis thaliana, a small weed that grows in most parts of the northern hemisphere. The vast majority of the world’s plant researchers utilise it in their research since the flowers naturally self-pollinate, produce many seeds, and allow researchers to go from one generation to another in 6 to 8 weeks.
“Therefore, we’ve got a lot of knowledge to build upon. Thale cress is easy to use because it has a limited number of cells. The plant is so anatomically simple that tracking and identifying abnormalities in it is easy”, says Annelie Carlsbecker.
The research group’s focus is on the vascular tissues of the plant. There, the xylem tissue transports water from the root to the sprout, and the so-called phloem carries the photo-synthetically produced sugar through the plant to the roots. To get a continuous water flow, long lines of xylem vessels must develop into a regular, functional pattern. The question scientists ask themselves is what regulates the development of patterns and the functions of various cells.
In that area, Annelie Carlsbecker was among the first in the world to discover that microRNA, a kind of sister molecule to DNA, plays a role in cell-to-cell communication. In 2010, she and her researcher colleagues in Finland and the United States published their findings in the scientific journal Nature. The study showed that microRNAs can move from the cell they are produced in to other cells, and even regulate how these develop.
“We saw that a layer of cells in the plant's root can send a microRNA signal to another layer of cells, which in turn responds. The microRNA regulates the levels of specific mRNA or messenger RNA, and thus affects the levels of proteins, which determine what type of cell the vascular tissue will consist of,” she says.
In the research group's laboratory, countless Arabidopsis thaliana seedlings huddle in small growing slabs. When the plants are around five days old, it is time to begin to study their development. One approach is to treat the seeds with a potent poison to produce mutations in the genes. When Annelie Carlsbecker worked as a post doc at the University of Helsinki “for a fantastic researcher, Ykä Helariutta”, she and her colleagues managed to produce a very specific mutation in their research objects.
“In a normal plant, some xylem vessels have spirally thickened cell walls. Other vessels, particularly those in the middle, feature more homogenous cell walls with tiny pores. But we got a mutant which only formed the second type of xylem vessels. We discovered that it was caused by an excess of a particular development-regulating protein, as the mutation prevented a microRNA to recognize and break down the mRNA of the protein.”
At the same time, their American colleagues found that another mutant exhibited the same aberrant pattern. It had been previously known among physiological botanists that the protein in question moves from within the vascular tissue to the surrounding cell layer. Now, they were able to show that this protein activates the microRNA in this cell layer.
“All in all, these discoveries put us on the right track so that we in 2010 could reveal that the activated microRNA moves from the surrounding cell layer into the vascular tissue,” says Annelie Carlsbecker. In the long run, the microRNA adjusts the level of a special form of development--regulating proteins. These proteins in turn determine the identities of the xylem vessels: a thinner type with spiral cell walls in the periphery and wider with a more intact cell wall toward the centre of the vasculature.”
This shows, according to Annelie Carlsbecker, how plant cells communicate with each other to ensure proper development. But it also opens up the possibility for external factors to influence this communication and thus plant development.
“Researchers had seen that for example poplars growing in dry areas feature many more and thinner water-transporting vessels. But otherwise, we knew very little about what is happening with the plant vasculature during drought.”
Her research group recently published a study of the effect of reduced water availability on the plant's vasculature, and the molecular mechanisms involved. It turns out that the response to the drought does not happen inside the vascular tissue. Instead, it is the surrounding cell layers that react by producing stress hormones and sending signals to the vascular tissue.
“During a drought, a stress hormone is generated that activates even more of the same microRNA that we had previously studied,” says Annelie Carlsbecker. “This leads to even lower levels of the proteins that regulate the development of the plant's xylem vessels. The roots therefore form more of the thinner xylem cells with spiral cell walls, similar to the cells in the wood of trees growing in a dry environment.”
One of her hopes is that the research will lead to such a detailed understanding such that the knowledge can be used for plant breeding purposes. With ongoing climate change, there is an increasing need for plants with great adaptability to everything from droughts to flooding - or still unknown challenges.
Annelie Carlsbecker therefore disagrees with the polarisation in large parts of the general public and, in particular, politicians painting a picture of genetically modified plants as something hazardous.
“I have a very hard time seeing the danger in all this. We have an extreme level of control and know exactly what we are doing. If we adjust a nucleotide, a gene, and it is deactivated, then that's exactly what we've done and nothing else. This is all very unfortunate for we are faced with the task of securing a healthy food supply for both us and our animals. We live off our plants, they make both our food and our oxygen, so we cannot survive without them.”
23 July 2018