Andre Velasquez: Plants on the defensive
May 17, 2017
Disease is one of the major issues holding back crop yield, with studies reporting annual productivity drops costing in the billions of dollars, which is why scientists are conducting large-scale studies to reduce crop losses around the world.
Recently, some people in the Sheng Yang He lab, where I work, and I wanted to find out how many types of defenses a plant could muster against bacteria. No other study has ever done that on a large-scale; at most, a few have tackled 20, 40, maybe 80 plant varieties at any one time.
We collected and examined 1,041 natural variations of one plant, called Arabidopsis, that mainly grows in Europe and Western Asia. Then we dipped them into pots full of harmful bacteria to see who would make it through unscathed.
Interestingly, plant immune systems don’t work like ours. When bacteria attack us, we produce antibodies tailored to fend them off, but plants are stuck with the defenses they are born with, like thorns, an almost impenetrable bark, or antimicrobial compounds. If a strain of a bacterium successfully infiltrates a plant once, the next time it attacks, chances are the plant will get sick again. It just can’t adapt like we can.
So it was important to know how our plants would fare against an invader they had never encountered before. We pit them against a bacterium that is a foe of tomatoes.
Only 14 out of more than 1000 plants actually fought off the bacteria. Admittedly, we subjected them to a severe test, more extreme than usual. The strategies ranged from surface defenses that prevent invasions, to molecular defenses that are activated once the bacteria breach through. In some cases, we didn’t know how the defenses worked, which shows the limits of our current knowledge.
We’re still years away from fully understanding plant defense strategies. Arabidopsis is just one plant. And although it is easy to work with – you can hold tens of thousands of seeds in one handful, and they grow fast, which makes it simple to do lab experiments quickly – it has no economic or food value.
However, we have to start somewhere. It’s tough to study diseases in agricultural crops. They grow much slower. And we can’t get our hands on as many variants as for Arabidopsis.
Ultimately, cataloging the basics of how plants resist disease might be the way to understand how this all works across different plant species.
And as our knowledge base increases, we can perhaps identify wild plants with specific defenses and cross them with their cultivated relatives. We could even genetically make plants that are more resistant to specific diseases.
We are still scratching the surface of what is possible. The number of plants, bacteria, viruses, and the interplay between them… there is a stunning variety of things going on in nature.