Abstract
The witches broom disease, caused by the basidiomycete Moniliophthora perniciosa [syn. Crinipellis perniciosa (Stahel) Singer; Marasmiaceae s.l.], is the most significant disease of cacao (Theobroma cacao). M. perniciosa can infect a variety of hosts, not only being restricted to cacao, allowing classification in three biotypes, C, L. and S. The C-biotype infects cacao and related species; the L-biotype infects lianas (vines) without inducing symptoms. The S-biotype colonizes solanaceae, and through artificial inoculation it is able to colonize the tomato (Solanum lycopersicum). Previous work carried out by our group showed that the tomato cultivar "Micro-Tom" (MT) is an adequate model for the study of the interaction with M. perniciosa, since the tomato presents symptoms of hypertrophy, stem hyperplasia, loss of apical dominance and formation of green brooms, and also demonstrated that cytokines play an important role in the development and progression of symptoms. These symptoms are also characteristic of infected cacao plants (C-biotype). Small non-coding RNAs play an important role in the interaction between plants and pathogens. These endogenous regulatory RNAs of 20-25 nucleotides do not encode proteins and are generally grouped into two major classes: interference RNAs (siRNAs) and microRNAs (miRNAs). MicroRNA156 downregulates most members of the SQUAMOSA PROMOTER BINDING-LIKE transcriptional factors (miR156 / SlSBP module). Such transcription factors are plant-specific and perform a variety of functions essential for plant development. Additionally, the miR156 expression pattern has been shown to be altered in response to infection by pathogens; however, to date, few studies have demonstrated the participation of such pathway in the interaction between plants and pathogens. Interestingly, overexpressing miR156 in MT tomato plants have some phenotypic characteristics that resemble M. perniciosa infected plants, such as loss of apical dominance and increase in the number of lobes in fruits. Therefore, the objective of this project is to evaluate the possible contribution of the miR156/SlSBP pathway and its correlation with cytokines in the interaction between S. lycopersicum and M. perniciosa (S-biotype), aiming to shed some light in the defense mechanisms or susceptibility to witches broom disease. The characterization of these pathways may contribute not only to a better understanding of the mechanisms associated with the interaction, but also to have potential future applications in the cacao improvement. (AU)
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