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The Plant Whisperer: Understanding the Communication between a Plant’s Roots and its Shoots

Do plants communicate? If so, how, what do they say and how does this help them grow? These sorts of questions have intrigued plant molecular and cell biologist, Byung-Kook (Brian) Ham. Ham, the research chair in plant molecular signaling at the Global Institute for Food Security (GIFS) is also assistant professor in the biology department at the University of Saskatchewan (USask). “Plant-speak” is his area of interest, specifically the communication that goes on between a plant’s roots and its shoots.  

“We know that the plant root is the primary organ for mineral nutrient uptake from the soil. Now, we’re also clearly seeing that root-to-shoot and shoot-to-root signaling plays a pivotal role in mineral nutrient uptake throughout the plant,” said Ham.

Ham moved to Saskatoon from the University of California Davis (UCDavis) in January 2018, to further his research in this area. He is studying the signals that run between a plant’s root system and its shoot tissues – its leaves, flowers, buds and above-ground stem. Much like humans have veins or vascular systems, plants also have vascular tissues, xylem and phloem, that transport water and nutrients through them.

When a plant has favourable conditions, like the right balance of temperature, water, nutrients and soil, its vascular tissue can transport and deliver what it needs to its various tissues for their development. This right balance is necessary for plants to make the food they need—the process known as photosynthesis. But what happens when growth conditions are not favourable and one or more of the elements needed are out of balance?

Enter root-to-shoot communication

Through his research, Ham has shown that plant roots are able to inform their shoots about a scarcity of nutrients. Indeed, the roots respond to the stressful conditions by generating molecular signals, which the vascular tissues send to the shoots. The shoots receive this information through the signals and are able to interpret what the nutrient limitations are. They in turn send signals back through the vascular tissues, instructing the roots on how to adapt to the limiting conditions so the plant can continue to grow.

“These molecular signals are generated in response to various stress conditions and are transported through the xylem and phloem, which function like an information superhighway within the plant,” says Ham.

Understanding this communication will help scientists learn how to increase the way plants use nutrients more efficiently. This is particularly important, as all plants need nitrogen, phosphate and potassium to grow well. Where there is a shortage of one or more of these nutrients, it is possible to supply them through fertilizers and other agricultural practices. However, research shows that the world will eventually run out of phosphates.

“Studying plant communication in nutrient-limiting conditions will help provide information on how to breed plants that can acquire and use mineral nutrients more efficiently. The efficient use of nutrients will lead to better crop outcomes, and by extension, improved food security,” said Ham.

So how does Ham study this root-to-shoot communication? Just as doctors can inject dyes into veins to examine them under an X-ray, Ham and his team at GIFS are studying the vascular-mediated transport of plant molecular signals using imaging systems. Various advanced imaging techniques exist, including certain types of scanners, X-rays and the synchrotron, which provides a brilliant light source that can show materials at the molecular level.

Recently, Ham was one of eight researchers at USask to receive a Canada Foundation for Innovation (CFI) John R. Evans Leaders Fund. His $225,000 award will fund the purchase of a confocal microscopy platform that will provide high-resolution real-time imaging of cells in plant vascular systems. These images will make it possible to analyze the molecules that communicate nutrient demand between plant roots and shoots.

Ham in a GIFS lab studying plant samples under a microscope

So vested is Ham in this research, that he has travelled around the world studying plant biology. He received his PhD in plant molecular biology at Korea University, South Korea in 2005, following which, he moved to UCDavis for a post-doctoral fellowship. After 12 years in UCDavis, during which time he rose to the rank of Associate Project Scientist, he made his way to Saskatoon to accept the research chair opportunity at GIFS and the faculty appointment in USask.

“I didn’t know much about Saskatoon, Saskatchewan, but I did know it had an excellent research and development ecosystem, including the University of Saskatchewan and the Global Institute for Food Security.”

What will success look like?

“Understanding root-to-shoot communication is vital to plant breeding,” said Ham. “Once we can identify how these molecular signals work, it will help scientists develop plants with more efficient root systems that can effectively sustain the plant’s optimal growth, even when soil nutrient conditions are less than optimal.”