Investigation of transcriptional alterations and microRNAs of the Theobroma cacao x Moniliophthora perniciosa pathosystem during the progression of witches' broom disease

Author(s)

Adrielle Ayumi de Vasconcelos

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2023-06-27

Examining board members

Gonçalo Amarante Guimarães Pereira; Isabel Rodrigues Gerhardt; Luciana Lasry Benchimol Reis; Marcelo Mendes Brandão; Eder Marques da Silva

• Advisor: Gonçalo Amarante Guimarães Pereira

Abstract

Witches' broom (VDB) of cacao (Theobroma cacao) is caused by the basidiomycete fungus Moniliophthora perniciosa, which has a hemibiotrophic lifestyle and different biotypes. Despite being one of the most limiting diseases of cocoa production in America, effective methods to control the disease do not yet exist due to the complexity of the pathosystem. In this work, using RNA-Seq, we investigated little-studied aspects of the molecular biology of this pathosystem, such as the transcriptional changes that occur during disease progression in cacao branches and roots, differences between fungal biotypes related to host compatibility, small regulatory RNAs and the adaptive evolution of fungal pathogenicity genes. In Chapter I, based on the transcriptomes of four moments of VDB in branches, we support that the biotrophic phase is characterized by high auxin response, degradation of plant carbon sources, and suppression of plant defense response by expression of pathogenicity factors by the fungus, which also employs other evasion strategies of the plant immune system. By analyzing some indicator genes, such as specific transcription factors, we also support the fact that the stage transition occurs with nutrient depletion in the infected branch. In the necrotrophic phase, the plant's ethylene response is induced, resulting in an intense oxidative stress defense response, which gradually culminates in branch senescence. At this stage, the fungus also expresses necrosis elicitor proteins, plant wall degrading enzymes and resistance genes that ensure its survival against the host defense response. In the roots, the sink effect of infected branches and the high energy expenditure of the defense response possibly lead to the reduction of root biomass, which showed repression of carbohydrate biosynthesis and auxin metabolism, impairing the development and growth of secondary roots. In Chapter II, we investigated the differences between a compatible interaction of M. perniciosa (C-biotype) and an incompatible one (S-biotype) with T. cacao in two initial times of the interaction. We identified genes involved in initiating the establishment of the biotrophic phase of the C-biotype, including effectors and a putative receptor potentially related to host specificity. On the other hand, the interaction with the S-biotype seemed to induce a possible rapid resistance response in the plant. In Chapter III, we identified microRNAs during the progression of VDB and performed the prediction of their target genes. Few miRNAs were predicted for M. perniciosa, most being induced in the necrotrophic stage. On the other hand, many miRNAs were differentially expressed by the plant, of which several were related to the regulation of genes involved in the response to hormones and in plant development and growth. In Chapter IV, through evolutionary analyzes of Pathogenesis Related-1 proteins in Moniliophthora genomes, we demonstrate that the evolution of these proteins can be shaped by the interaction with the host in this genus, which can generate neofunctionalized and even exclusive copies between species and between biotypes. Finally, this work revealed a large amount of new information about the pathosystem that can help in its understanding and in the direction of new studies and development of solutions (AU)

• FAPESP's process: 17/13015-7 - Investigation of global transcriptional alterations in the Theobroma cacao x Moniliophthora perniciosa pathosystem during the progression of Witches Broom Disease of cacao
• Grantee: Adrielle Ayumi de Vasconcelos
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)