Studying gravitropism in lateral roots

Arabidopsis seedlings showing lateral rootsQuick, what’s the first thing you think of when you think about plants? A tree? Leaves? A flower? Chances are slim that you thought first of a root, yet roots make up nearly half of the typical plant’s body. They are the hidden side of the plant, feeling their way in the dark, around stones and through soil, in search of the water and minerals needed for survival. They sense things like moisture gradients, solid objects like rocks and pebbles, and can tell up from down, using these cues in ways that remain largely unknown to guide their growth. Considering that we humans are completely dependent upon our photosynthetic, green cousins for the food we eat and the air we breathe, and considering the vulnerability of plants to drought, we would do well to learn more about how roots do what they do.

Despite making up the vast majority of the root system, how lateral roots choose their path remains uncharted territory. For example, lateral roots are content to grow sideways for long periods, a situation that is anathema to primary roots, which react swiftly with a course correction when they find themselves growing sideways. It isn’t like lateral roots are unable, however, to mount such a course correction. When displaced from their route, they will return to it, whatever it was. But when the course was not-quite-vertical, how do they know where to go? Are they using the same cellular tools as the primary root to detect gravity? Are the same circuits that activate curvature in the primary root activated in lateral roots? Given their role in nutrient uptake, do lateral roots change their course when nutrient conditions change? In our most recent paper, we set out to address some of these questions about lateral root growth. Over the coming weeks, I’ll be posting more on how we carried out our experiments and what we found out.

AJB Special Issue on Tropisms

I am honored to have a paper in this month’s American Journal of Botany, a special issue focused on plant tropisms. Below is a collection of links highlighting some of the work:

Scientists join forces to bring plant movement to light:

Elementary school students often learn that plants grow toward the light. This seems straightforward, but in reality, the genes and pathways that allow plants to grow and move in response to their environment are not fully understood. Leading plant scientists explore one of the most fundamental processes in plant biology—plant movement in response to light, water, and gravity—in a January Special Issue of the American Journal of Botany.

Low Phosphate Alters Lateral Root Setpoint Angle and Gravitropism (our paper):

Lateral root orientation and gravitropism are affected by Pi status and may provide an important additional parameter for describing root responses to low Pi. The data also support the conclusion that gravitropic setpoint angle reacts to nutrient status and is under dynamic regulation.

I’ll post again on the work that went into our paper, including a breakdown of the inputs of time and talent that made this work possible. In short though, three awesome students worked many hours in the lab over the course of four years to produce these insights.

Gravitropism goes mainstream

How Do Plants Know Which Way Is Up And Which Way Is Down?:

Think of a seed buried in a pot (…) It’s dark down there in the potting soil. There’s no light, no sunshine. So how does it know which way is up and which way is down? It does know. Seeds routinely send shoots up toward the sky, and roots the other way. Darkness doesn’t confuse them. Somehow, they get it right…

As the resident expert on gravitropism, I had several friends send me this link, excited that they “knew all about this”. Krulwich takes this example from David Chamovitz’s new book, What a Plant Knows. He goes on to explain in words and drawings the concept of the starch-statolith theory of gravity sensing in plants. It’s an old concept that continues bearing fruitful research, as demonstrated by our recent work studying gravitropism in a starchless mutant.