Plant Email System Described

What do you call a long-distance signaling system that involves coded information?

Japanese researchers identified a coded string of information that acts as a signal, but it wasn’t intercepted email: it was a molecule inside a plant, the humble lab plant Arabidopsis thaliana. Phys.org says that scientists at Nagoya University identified a polypeptide that tells roots when the top of the plant is starved for nitrogen, essentially telling the roots to send some up pronto.

The polypeptide is not a random string of amino acids. It’s an ordered sequence that must be recognized by the plant to generate a purposeful response. The article shows that this is a two-way communication pathway, something like email with a molecular message:

Although not able to actively forage for their food, plants can nevertheless overcome problems relating to nutrient scarcity or varied distribution using a long-distance signaling mechanism. This helps determine their competitive success and productivity. For instance, nitrogen (usually in the form of nitrate) is essential for plant growth, but is often only present as patches in the soil. Nitrogen-starved roots express a mobile plant hormone (CEP) that travels upward to the shoot and eventually triggers compensatory nitrogen uptake by roots in more nitrogen-rich areas. This CEP signal is received by a receptor protein in the leaves, but the molecules involved in the shoot-to-root response signal were unknown.

That’s just the first signal, from root to shoot. When the leaves in the shoot receive the signal, they switch on genes that are only activated in the shoot. To complete the communication circuit, the message needs to get back down to the root. Expecting to find one, they intercepted the message:

The team showed that these polypeptides accumulated in the roots, although the genes encoding them were expressed only in the shoots. This indicated that the polypeptides act as mobile descending shoot-to-root signals.

Rounding out the comparison to an email system, the article shows that this is no simple thing:

Such a sophisticated signaling system ensures that plants maximize the efficiency at which they obtain nutrients, and could be exploited to improve fertilizer application and enhance plant productivity.

Well, what do you know! Plants have an intranet, and they communicate with email. That should cause some interesting conversation at the water cooler. You don’t need to email your office plants, though; they speak a different language.

Update 4/08/17: A paper in Nature Scientific Reports examines the “synergistic response” between roots and leaves in drought conditions. The authors speak of signals, crosstalk and feedback loops that keep all parts of the plant in touch with each other.

When subjected to drought, leaves were more sensitive than roots and seedling morphology changed significantly. Some physiological changes were irreversible if the drought period exceeded 24 h. Energy and protein metabolism are stimulated in roots responding to drought stress but inhibited in leaves. Drought significantly inhibits photosynthesis in leaves. In both roots and leaves, 14-3-3-like protein A played a key role in the synergistic response to drought stress defined by our PPI network analysis. The key to understanding the signal transduction processes involved in the response to drought stress may be found in the crosstalk pathways that connect roots and leaves under these conditions. Our results provide new insight into the molecular mechanisms plants adaptation to tolerate drought stress.

They ran experiments on a member of the grass family. Think about what’s going on under your feet when you walk on the lawn. To the blades of grass, it might be like an EMP attack on their communications network, but apparently, they have good recovery systems in place.

We first reported the possibility of “plant email” in the early days of CEH (7/13/01), and have not lost fascination with it. This story shows that the concept is still proving fruitful in advancing scientific knowledge. Notice that a string of amino acids is meaningless without an interpreter, and that genes at both ends of the plant have to understand the language convention. The system is irreducibly complex because all the sophisticated parts must exist simultaneously for there to be any function at all. Communication systems in living things bear the hallmarks of intelligent design – that is, to all who have not been brainwashed into supposing that “stuff happens” qualifies as a scientific explanation.