Apoplastomes of contrasting cacao genotypes to witches' broom disease reveals differential accumulation of PR proteins

Witches' broom disease (WBD) affects cocoa trees ( L.) and is caused by the fungus that grows in the apoplast in its biotrophic phase and later progresses into the tissues, causing serious losses in the production of cocoa beans. Therefore, the apoplast of can provide important defense responses during the interaction with . In this work, the protein profile of the apoplast of the genotypes Catongo, susceptible to WBD, and CCN-51, resistant one, was evaluated. The leaves of were collected from asymptomatic plants grown in a greenhouse (GH) and from green witches' brooms grown under field (FD) conditions for extraction of apoplastic washing fluid (AWF). AWF was used in proteomic and enzymatic analysis. A total of 14 proteins were identified in Catongo GH and six in Catongo FD, with two proteins being common, one up-accumulated, and one down-accumulated. In CCN-51, 19 proteins were identified in the GH condition and 13 in FD, with seven proteins being common, one up-accumulated, and six down-accumulated. Most proteins are related to defense and stress in both genotypes, with emphasis on pathogenesis-related proteins (PR): PR-2 (β-1,3-glucanases), PR-3 and PR-4 (chitinases), PR-5 (thaumatine), PR-9 (peroxidases), and PR-14 (lipid transfer proteins). Furthermore, proteins from microorganisms were detected in the AWF. The enzymatic activities of PR-3 showed a significant increase (p < 0.05) in Catongo GH and PR-2 activity (p < 0.01) in CCN-51 FD. The protein profile of the apoplastome offers insight into the defense dynamics that occur in the interaction with the fungus and offers new insights in exploring future WBD control strategies.