CITRUSBUSTERS supported a new review published in The Plant Journal by the Centro de Biotecnología y Genómica de Plantas (CBGP) at the Universidad Politécnica de Madrid. It explains how plants recognise danger, and how this knowledge could support greener crop protection.

Published in May 2026 in The Plant Journal; doi: 10.1111/tpj.70876
Authors: Vílchez-Pinto, Garrido-Arandia, Molina, Torres and Jordá, CBGP, UPM-INIA/CSIC, Madrid

When a citrus tree is attacked by a fungus or an insect vector, it cannot rely on antibodies.

Plants do not have specialised immune cells like animals. Instead, they use a different defence system. Every plant cell carries molecular sensors on its surface. These sensors read chemical warning signs from the outside world. They are called pattern recognition receptors, or PRRs. One of their most important jobs is recognising sugars.

Why sugars matter

Sugars, known in science as glycans, are everywhere in biology. They cover the surface of bacteria and fungi. They help build plant cell walls. When a pathogen attacks, small sugar fragments can break off. These fragments become warning signals. The plant reads them as a message: danger is here.

A new review published in The Plant Journal by a team from the Centro de Biotecnología y Genómica de Plantas (CBGP) at the Universidad Politécnica de Madrid, with funding support from CITRUSBUSTERS through Miguel Ángel Torres’ contribution, looks at exactly this process. The article “Structural insights into glycan recognition by plant immune receptors: a comparative perspective with animal innate immune systems” does something both ambitious and useful. It compares what we know about how plant immune receptors detect sugars with the much-better-understood story of how mammalian immune receptors do the same thing. The result is useful far beyond basic science. It could help researchers design new crop protection tools based on the plant’s own immune system.

Two types of warning signals

The review focuses on two main types of molecular flags. MAMPs (microbe-associated molecular patterns) are sugar signatures unique to invaders. DAMPs (damage-associated molecular patterns) are sugar signatures released when the plant’s own cells are damaged.

MAMPs are signals that come from microbes. They tell the plant that a bacterium, fungus or other invader may be present. DAMPs come from the plant itself. They are released when plant tissue is damaged. Both can activate plant immunity. Calcium signals rise inside cells. Defence genes switch on. Antimicrobial proteins are produced. The plant prepares to fight.

What the review found

Three takeaways stand out from the comparison of plant and animal systems.

Plants have their own immune toolkit. Plants and animals both recognise sugar signals. But they mostly use different molecular tools to do it. One important exception is a receptor module called LysM, which appears in both systems. Beyond that, plants seem to have evolved their own way of reading sugar-based danger signals.

Plant receptors come with a built-in signalling engine. Many plant immune receptors combine two jobs in one molecule. Outside the cell, they bind the danger signal. Inside the cell, they help pass the message on. This built-in design can make the response direct and efficient.

Structural biology can make crop protection more precise. Scientists know a lot about how mammalian immune receptors grip sugar molecules. Plant research is now catching up. With tools such as X-ray crystallography, cryo-EM and AI-based protein modelling, researchers can start to predict how plant receptors recognise specific sugars.

Why this matters for crop protection

The European Union is committed to cutting pesticide use by 50% by 2030. Agriculture urgently needs alternatives and one of the most promising is plant immune elicitors: molecules that, when applied to a crop, switch on the plant’s own immune system. The plant defends itself, naturally, with no synthetic chemistry left behind.

The challenge with elicitors today is precision. We don’t yet fully understand which sugar shapes the plant’s receptors recognise, or how strongly. That makes elicitor design slow and largely trial-and-error.

The review argues that structural biology, supported by AI, is now sophisticated enough to change that. On one hand, identifying these signals opens the possibility of “vaccinating” plants, treating them with defined molecules that prime and activate their defences in advance. On the other hand, mapping the exact way a plant PRR grips its sugar ligand opens the door for breeding programmes, enabling the development of crops with enhanced or broader immune recognition. Together, these advances pave the way for the rational design of targeted elicitors, tuned to switch on the plant’s immune system efficiently, without harming non-target species or leaving residues. Without that knowledge, discovery can be slow.

What comes next

The review also points to important open questions. How do several plant receptors work together? How do receptor complexes form at the cell surface? How can plant immunity be activated without harming beneficial microbes?

These key challenges will be among the questions CITRUSBUSTERS and its partner labs keep working on in the years ahead. The better we understand the molecular language of plant immunity, the closer we get to crops that can defend themselves.