Latest Insights into Plant Defense Mechanisms

Gundula A. Noll

        "The better we understand how plants activate their natural defenses, the more effectively we can help them do so. This has many benefits: We can reduce the use of chemicals, protect the environment, and breed hardy varieties that can withstand new pathogens, especially in the face of climate change."

A recent multidisciplinary study led by Dr. Alexandra Furch of the University of Jena in collaboration with apl. Prof. Dr. Gundula Noll and Professor Dirk Prüfer at Fraunhofer IME in Münster, along with further experts, explores how plants convert the perception of pathogens into electrical signals, thereby triggering local and systemic defense responses. Surprisingly, the results suggest that structural phloem proteins, which until now have been primarily associated with the closure of sieve plates following injury, may also be involved in signal transduction.

The research team investigated Arabidopsis thaliana and Vicia faba, revealing that the density of the pathogen receptor (FLS2) is notably high in the epidermis and vascular parenchyma. In the mesophyll, it is low, and there are virtually no FLS2 receptors in the sieve elements (SEs).

Recognition of the conserved bacterial flg22 peptides by the plant leads shortly thereafter to the emergence of double cytosolic Ca²⁺ spikes. These correlated with voltage shifts extending from the epidermis to the sieve elements. These electrical signals manifest as rapid long-range action potentials (APs) or slower short-range variation potentials (VPs).

In A. thaliana, the two SEO proteins AtSEOR1 and AtSEOR2 act in tandem during sieve element occlusion. To further analyze their role in defense against phytopathogenic bacteria, the researchers generated the Atseor1/2 double knockout line. Wild-type plants (SEO-competent) and Atseor1/2 double-knockout plants (non-SEO-competent) were locally inoculated with the bacterium Pseudomonas syringae, which frequently causes agricultural plant diseases. After three days, the researchers observed a significantly increased susceptibility in the mutants compared to the wild-type plants. This result highlights the importance of sieve element closure for plant pathogen defense.

Overall, the results not only provide new insights into the mechanisms of plant signal transduction and defense. They also open up prospects for the further development of disease-resistant crops through the targeted manipulation of relevant signaling and transport processes.