Molecular chaperone modulation in cocoa leads to plant resistance to Moniliophthora perniciosa

Moniliophthora perciciosa, the causal agent of witches’ broom disease, is one of the major cocoa pathogens that affects cocoa farming in South and Central America. The control of this phytopathogen is usually carried out by replacing plants with resistant genotypes accompanied by phytosanitary pruning. The identification of plant genes that are related to the plant's defense mechanism is important not only to unravel the molecular basis of plant-pathogen interaction but also to identify new strategies to combat the pathogen. Research often seeks to identify genes that code for PRs (pathogenesis related proteins), a set of novel proteins associated with host defense which prevents the pathogen progress. PR proteins exist in plant cells intracellularly, also in the intercellular spaces, particularly in the cell walls of different tissues. In so, most PRs are secretory proteins and are translated and assembled in the lumen of the Endoplasmic Reticulum (ER). The Biding Protein (BiP) is a molecular chaperone located in the ER lumen that binds newly-synthesized proteins as they are translocated into the ER and maintains it in a competent state for subsequent folding and oligomerization. BiP is an abundant protein under all growth conditions, but its synthesis is markedly induced under conditions that lead to the accumulation of unfolded polypeptides in the ER as when plants are under pathogen attack. In the present study, we superexpressed BiP in tomato plants, a model plant susceptible to M. perniciosa. Ten transgenic lines showing different BiP levels on western blot analyzes, were inoculated with M. perniciosa spores. After 60 days, we observed that all control plants (not transformed) presented severe witch’s broom disease symptom, while transgenic lines symptom varied from severe to mild according to BiP level. In so we observed a positive correlation between BiP accumulation and M. perniciosa plant’s tolerance. Our results suggests that BiP might have a protective activity against pathogen attack. It is possible that under accumulation of BiP in ER lumen, secretory proteins as PRs are more promptly assembled giving the plant a molecular advance in responding to the pathogen infection. More research needs to be done in order to better understanding the molecular basis of the induced resistance. However, our results brings the notion that it might be possible to develop new strategies to control the pathogen based on the induction of endogenous cacao Molecular chaperones, as BiP.