Pršić, J.

2024

Abstract: In recent years, the induced systemic resistance (ISR), triggered by elicitors produced by plant beneficial bacteria, emerged as a promising strategy for implementation in sustainable agriculture. Compared to chemical pesticides, ISR has certain advantages, such as provision of long-lasting and broad-spectrum protection and a low risk of development of resistant pathogens. Among ISR elicitors, cyclic lipopeptides (CLPs) are particularly important. Being reported in high diversity of phytopathosystems, the most studied CLP as an ISR elicitor is surfactin (Srf) produced by beneficial bacilli. However, the success of plant beneficial bacteria as stimulators of ISR has been rather limited due to a number of factors, including our global lack of knowledge about the mode of action of their elicitors. The aim of this work was therefore to investigate the elusive phenomena of ISR induced by these beneficials, using Srf as a model elicitor.To tackle this complex question, this work integrated biophysical, in silico, and in planta approaches. The first method was to compare immune responses triggered by Srf and a well-known pattern triggered immunity (PTI) elicitor flagellin 22. Being the first steps in immunity elicitation, perception by the plant cells and mechanisms for early immune events elicitation were firstly investigated. Furthermore, a genome-wide transcriptome analysis was performed to compare these two types of responses at the transcriptional level. The data indicated that Srf does not rely on previously described elicitors sensing receptors, but rather interacts with the lipid phase of plant plasma membrane (PPM). More specifically, Srf interacts with a specific class of lipids, causing changes in PPM lipid organization, structural and rheological properties. Such membrane changes have been described in the literature to be perceived via mechanosensitive ion channels, and this work shows that representatives of these channels are required for early immune responses activation and induction of ISR by Srf. In addition, genome-wide transcriptome analysis revealed that plant responses to Srf and during the onset of PTI significantly differ. Considering that the bioactivity of Srf is influenced by the presence of particular PPM lipids, other structurally different CLPs were tested, and it was observed that the affinity for lipids differs among them. This indicates that in different species, CLPs/PPM lipids interaction will result in different immune responses depending on plant’s plasma membrane lipid profile. Further structure activity studies revealed that CLP activity is a finely tuned process where structural changes in both the peptide and the acyl chain can cause loss of activity.Through in-depth data mining of results of the RNAseq analysis conducted on Arabidopsis thaliana roots, this work also provided data that could be used to decipher signaling during the onset of Srf-triggered ISR, as well as the mechanism for enhancing plant defense responses.Abstract2To our best knowledge, this is not only the first time that a perception of an ISR elicitor has been described, but also the first time that this peculiar way of perception of an immunity elicitor was described. Moreover, by revealing the perception pathway and the transcriptional changes induced upon Srf treatment, this work provides clues for further elucidation of Srf triggered ISR.

Keyword(s): Earth, Environment and Cultural Heritage (1st) ; Biology (2nd) ; Chemistry (2nd)

1. MARIA (MARIA)

1. MARIA: Magnetic reflectometer with high incident angle (NL5N)