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Biologist Kaisa Kajala conducts research on the evolution of the exodermis, a protective layer in the roots of flowering plants. With the Vidi grant of 800.000 euros she received in November, she wants to breed legume plants that are both climate change resilient and, at the same time, mitigate climate change themselves.

Kaisa Kajala is originally from Finland. “However, I haven’t lived there since I finished high school. I started studying at Cambridge right away and have gained my bachelor’s and PhD degree in the UK. I don’t have a master’s: for most biology courses at Cambridge, that’s not obligatory if you flow into a PhD directly. Your first PhD-year then equals a master.”

After obtaining her PhD, Kajala worked as a postdoc at the ľ�ϸ���Ӱ�� of California Davis for five years. “There, I studied the gene expression in tomato plant roots. We have developed transgenic marker lines with which we could study the gene expression of each cell type in the roots of tomato plants. With that, you can for example determine how each cell responds to environmental factors such as drought.” With a certain sense of pride: “We have made an atlas for the gene expression in the root.”

We know little about the exodermis that is present in 80% of all flowering plants, as our model plant Arabidopsis lacks an exodermis.

In love

It was at UC Davis that Kajala “fell in love” with one specific type of tomato root cell: the exodermis. ”These cells form a layer, just beneath the outer cells of the root. The exodermis cells excrete the two long molecules suberin and lignin, which are the main components of cork and wood, respectively. Together, they form a protective barrier.”

“The tomato, and together with it 80% of all flowering plants, has an exodermis. “But we know little about it and that is caused by the fact that it lacks in the model plant Arabidopsis. Deeper inside the root, there is a comparable layer called the endodermis, which is present in all plants. For a long time, biologists assumed that the flowering plants’ exodermis has the same function and similar genetics as the endodermis in plants that lack an exodermis. By now, we know that we can translate surprisingly little endodermis knowledge. The Arabidopsis endodermis is more comparable to the tomato plant’s endodermis after all.”

Oxygen to the root

The exodermis protects plant roots against their surroundings within the soil. “Against everything really: against drought and salinity by keeping water inside the root, against toxics compounds and pathogens.” Apart from that, different plant groups use their exodermis differently. “Rice uses the space between endodermis and exodermis to transport oxygen all the way from the leaves to the root tip and exodermis keeps that oxygen from escaping into the soil.”

Kajala would like to understand the molecular changes that are the basis to the exodermis’ function and evolution. “That is why, during the next five years, I will compare a series of legumes, together with a postdoc and a PhD-candidate. In legumes, based on their genetic codes, the evolution of exodermis seems to have happened in steps. If we can find a genetic regulator for exodermis, we can breed plants with the right genes for stronger exodermis barriers.”

Climate change

The work offers perspective for plants’ adjustment to climate change and the drought and flooding events that, consequently, happen more frequently. “Breeding for crops that are more resilient against these events would help us secure our future food supply. The model plants for this Vidi work, legumes, contain many field crops and sources of plant protein: soy, beans, peas and lentils. This eases the translation of the research into applications.”

Interestingly, exodermis according to Kajala also has the potential to combat climate change. “The suberin and lignin that form the exodermis barrier, are among the slowest degrading components in the soil. This makes the exodermis barriers a good way to tie up carbon into the soil. Hence, it may be possible to reduce atmospheric carbon dioxide by capturing more carbon into the soil through growing plants with stronger exodermis barriers.”