Endogenous RALF peptide function is required for powdery mildew host colonization

Area of Science:

• Plant-pathogen interactions
• Molecular plant pathology
• Plant immunity and susceptibility

Background:

• The receptor kinase FERONIA (FER) is known as a susceptibility factor for powdery mildew in Arabidopsis thaliana.
• FER perceives endogenous RAPID ALKALINIZATION FACTOR (RALF) peptides, influencing plant growth, development, and immunity.
• RALFs interact with FER/LORELEI-LIKE GPI-ANCHORED PROTEIN (LLG) complexes or LEUCINE-RICH REPEAT EXTENSIN (LRX) proteins, affecting cellular responses and cell wall structure.

Purpose of the Study:

• To elucidate the molecular mechanisms by which FER and RALF peptides contribute to powdery mildew susceptibility in Arabidopsis.
• To investigate the roles of LLGs and LRXs in the interaction between Arabidopsis and powdery mildew fungi.
• To understand how RALF-mediated processes like cell wall remodeling and apoplastic pH homeostasis impact fungal colonization.

Main Methods:

• Genetic analysis of Arabidopsis mutants and wild-type plants.
• Cell biological techniques to visualize cellular processes.
• Biochemical assays to study protein interactions and peptide functions.

Main Results:

• Endogenous RALF ligands perceived by FER are essential for the successful colonization of Arabidopsis by Erysiphe cruciferarum.
• LLGs and LRXs also function as susceptibility factors for powdery mildew.
• RALF-mediated cell wall remodeling and apoplastic pH homeostasis promote fungal reproductive success, with RALF-dependent pathogenesis being partially independent of FER.

Conclusions:

• Powdery mildew fungi likely rely on endogenous plant RALFs, rather than producing mimics, for successful host colonization.
• RALF-mediated modulation of apoplastic pH and pectin remodeling represents a novel susceptibility mechanism exploited by obligate biotrophic fungi.
• This study highlights a new avenue for understanding plant susceptibility to fungal pathogens.