Plant Diseases: What I Study

Mar 10, 2016 By Carolina Grandellis
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I find plants fascinating because they can produce their own food directly from sunlight: plants do photosynthesis to convert light and carbon dioxide from the sun into chemical energy in the form of sugar.

Plants also need to capture water from the roots to do that, and oxygen is released during the process. Photosynthesis then maintains oxygen levels in the environment necessary for life on Earth.

Also, since plants are sessile, meaning they cannot walk or run, they are at the mercy of the environment. They face pathogens and nasty environmental conditions and must fight against them. How do plants do that? Do they have an immune system like us to protect themselves?

Studying Citrus Canker

My research is about plant diseases. Plants, as animals, also get sick when a bacteria, virus or fungi invades them. These are plant-pathogens or phytopathogens.

I am studying a bacteria which causes a disease in Citrus species. Citrus is an important source of fruits: oranges, grapefruit, limes and lemons. The bacteria is called Xanthomonas citri and causes a disease called Citrus Canker. Citrus Canker generates lesions on leaves, stem and fruits of the Citrus trees.

Cankers affect the vitality of the trees, and the leaves and fruits drop earlier, affecting the yield (the amount of fruit produced). Even though the disease is not a threat to humans directly, many countries from Europe will not buy the infected fruits because they don’t want their plants to get infected.

In my country, Argentina, fruit production is very important. Argentina is the eighth producer of Citrus worldwide. That is why we are looking for solutions to help the plant get better after the infection, and stay healthy.

Using A Model Plant First...

With Citrus Canker, when the bacteria enters the plant, it infects the vegetal tissue. I am trying to identify how molecules from the bacteria enter the plant and produce the disease.

We don’t always study the disease in Citrus plants. Sometimes we use what is called a model plant, the most popular is Arabidopsis thaliana, because is very easy to work with in the lab. This is similar to animal research, where we sometimes use mice before testing on humans to learn if a new vaccine works.

Similarly, we first analyze the disease in this model plant, and then try to reproduce our results in the crop of interest, Citrus in my case. If we understand the molecular basis of this plant-pathogen interaction, we can then find a way to disrupt this interaction, to prevent the bacteria from entering the plant cells.

To do that, I recreate the infection in the lab, by growing the bacteria in tubes and then putting in contact with the leaves. After some time, I collect the plant tissue and extract the protein, the DNA and RNA, and study the genes and proteins that are activated, during the infection. Based on that, I understand how the plant is fighting the disease. I can construct a map of the molecules that produce the disease and what defenses the plant has.

This information is helping us find ways to make sure these important plants don’t get sick, and can produce great fruit for us.