Plants have their cake and eat it too
Scientists have thought for a long time now that plants have a remarkable ability to grow or defend themselves, but they don’t do a good job doing both functions at the same time.
The Howe lab has created a plant that challenges that assumption, and the future implications for agriculture and food security could be very significant.
“The long-held idea makes intuitive sense,” says Dr. Gregg Howe, co-author of the study. “If you think about it, plants work with a limited amount of resources, and it would seem like they would prioritize these resources for particular processes – in this case, growth or defense – depending on the need.”
Casual observations would confirm this concept, known as the defense-growth trade-off. Plants that defend more are smaller, yet plants that grow more have severely weakened defenses.
Creating a genetic test
Marcelo Campos, a former graduate student in the Howe lab and lead co-author of the study, wondered if they could devise a genetic approach to somehow make a plant that can have it both ways.
“To be honest,” says Dr. Gregg Howe, “I was a bit skeptical at first, because it’s impossible to predict how a random combination of genes will affect an organism’s interaction with the environment. But I encouraged him to go ahead and try it.”
First, it was necessary to create a plant – which they named jazQ – that produced high levels of defense compounds at all times, even when the plant was under no threat from insects.
The jazQ plant was indeed remarkably resistant to insect attackers but, as predicted by the defense-growth trade-off idea, also grew much slower than its wild counterparts.
Taking the next step, the lab randomly mutated thousands of jazQ plants to see if they could find a fast growing plant that retained the high defense feature. The team found that some plants grew fast, but they had lost their ability to defend in the process.
But, and to the researchers' surprise, one stood out.
“Have Your Cake and Eat It Too”
All plants have molecular pathways dedicated to the production of proteins, hormones, or other molecules that are used to develop and protect the plant. An analogy would be the logistical network of drivers, warehouses, and communications systems that work together to deliver a package from its starting point right to your doorstep.
It turns out that molecular pathways for plant growth and defense are generally antagonistic to each other. So when one is more active, the other tends to be reduced.
Looking closer at the new plant, the researchers found a very interesting mechanism to explain how it worked. The specific mutation, which removed a photoreceptor (called phytochrome B) that is part of the growth pathway and is responsible for detecting red light, suddenly dissolved the antagonism, and both pathways appeared to work at full capacity.
“Our lab has been joking around that this plant has its cake and eats it too!’”
Dismantling the Defense-Growth Trade-off
“There must be some other reason why stressed plants grow more slowly than non-stressed plants. This is a phenomenon that is also seen in animals and bacteria, so why do stressed plants grow slower?” That is next on the lab's agenda.
“Down the road, we are also interested in applying this genetic combination to crop plants”, says Ian Major, study co-author and post doc in the Howe lab.
For example, packing crops, such as corn, closer together increases yield. But increased planting density results in crops growing taller as they compete intensely for sunlight, which makes them vulnerable to insects and pathogens.
“But if we make appropriate genetic modifications through breeding or molecular approaches, we can hopefully help design the next generation of crops to meet the food and fuel demands of the growing world population.”
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