Investigation of the role of auxin produced by the fungus Moniliophthora perniciosa in the development of witches' broom disease in cocoa trees

• Grant number: 23/10167-1
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: November 01, 2023
• End date: January 31, 2026
• Field of knowledge: Biological Sciences - Genetics - Molecular Genetics and Genetics of Microorganisms
• Principal Investigator: Paulo José Pereira Lima Teixeira
• Grantee: Nathália Cassia Ferreira Dias
• Host Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil
• Associated research grant: 18/24432-0 - Functional characterization of effector proteins from cacao pathogens and search for their cognate immune receptors, AP.JP

Abstract

The cocoa tree (Theobroma cacao) provides the raw material for chocolate production and is a culturally and economically significant crop for various countries in Latin America, including Brazil. However, the cultivation of cocoa trees in the American continent has been severely limited for several decades due to various diseases caused by fungi and oomycetes. Among them, the most important in Brazil is witches' broom disease, which is caused by the hemibiotrophic basidiomycete Moniliophthora perniciosa. Plants affected by witches' broom exhibit intense morphological alterations indicative of hormonal imbalance, including the development of abnormal branches with excessive growth. Recently, our group found that plants infected by M. perniciosa show high expression of genes responsive to auxin, which could explain the main symptoms of the disease. Interestingly, cacao genes involved in auxin synthesis are not induced in infected plants, leading us to hypothesize that the pathogen may be responsible for inducing the auxin response in the host. Indeed, we verified that M. perniciosa is capable of producing indole-3-acetic acid (IAA) when supplemented with tryptophan, the precursor of this auxin. Thus, we hypothesize that M. perniciosa produces auxin as a virulence strategy during its infection of the host. Despite the role of auxin in plant-pathogen interactions still being poorly understood, this hormone can suppress defense responses mediated by salicylic acid, favoring the colonization of biotrophic and hemibiotrophic pathogens. In this project, we will evaluate whether the auxin produced by M. perniciosa contributes to the suppression of the cacao immune system and/or to the development of the morphological alterations observed in infected tissues. To do this, we will produce mutants incapable of producing IAA using the CRISPR/Cas9 system. Protocols for the transformation of this fungus were recently established in our laboratory, and genes potentially involved in IAA synthesis have already been identified. Once obtained, mutants unable to produce this hormone will be inoculated into cacao seedlings, and the plants will be evaluated for symptom incidence. Thus, in addition to exploring a central aspect of the biology of this disease, this project will also investigate the role of auxin in the virulence of microorganisms, a topic that is still relatively unexplored in plant-pathogen interactions.