Cocoa Apoplastome Contains Defense Proteins Against Pathogens

Area of Science:

• Plant pathology
• Plant biochemistry
• Proteomics

Background:

• The apoplast plays a crucial role in plant defense mechanisms.
• Witches' broom disease (WBD), caused by *Moniliophthora perniciosa*, affects *Theobroma cacao* (cacao) by initially colonizing the apoplast.
• Understanding the apoplast's role in cacao-fungus interaction is key to managing WBD.

Purpose of the Study:

• To conduct the first apoplastic proteomic mapping of cacao genotypes contrasting in WBD resistance.
• To identify proteins involved in the *T. cacao*-*M. perniciosa* interaction during the biotrophic phase.
• To explore potential resistance markers and defense strategies against WBD.

Main Methods:

• Apoplastic washing fluid (AWF) collection from two cacao genotypes (CCN51-resistant and Catongo-susceptible).
• Two-dimensional gel electrophoresis for protein separation and identification.
• Proteomic analysis to map proteins in the AWF.

Main Results:

• Identified 36 proteins in the resistant CCN51 genotype and 15 in the susceptible Catongo genotype.
• Highlighted pathogenesis-related (PR) proteins like peroxidases, β-1,3-glucanases, and chitinases.
• Detected osmotin as a potential resistance marker in CCN51 and increased superoxide dismutase (SOD) activity in both genotypes under field conditions.
• Observed significant inhibition (>80%) of *M. perniciosa* basidiospore germination by cacao AWF.

Conclusions:

• The apoplast is vital for cacao defense against *M. perniciosa* during the initial infection phase.
• Identified specific proteins and enzymes (e.g., osmotin, SOD) that could serve as WBD resistance markers.
• AWF exhibits antifungal properties, suggesting potential for novel WBD control strategies targeting the apoplast.