Transcriptomics and systems biology analysis in identification of specific pathways involved in cacao resistance and susceptibility to witches' broom disease

Abstract

This study reports on expression analysis associated with molecular systems biology of cacao-Moniliophthora perniciosa interaction. Gene expression data were obtained for two cacao genotypes (TSH1188, resistant; Catongo, susceptible) challenged or not with the fungus M. perniciosa and collected at three time points through disease. Using expression analysis, we identified 154 and 227 genes that are differentially expressed in TSH1188 and Catongo, respectively. The expression of some of these genes was confirmed by RT-qPCR. Physical protein-protein interaction (PPPI) networks of Arabidopsis thaliana orthologous proteins corresponding to resistant and susceptible interactions were obtained followed by cluster and gene ontology analyses. The integrated analysis of gene expression and systems biology allowed designing a general scheme of major mechanisms associated with witches' broom disease resistance/susceptibility. In this sense, the TSH1188 cultivar shows strong production of ROS and elicitors at the beginning of the interaction with M. perniciosa followed by resistance signal propagation and ROS detoxification. On the other hand, the Catongo genotype displays defense mechanisms that include the synthesis of some defense molecules but without success in regards to elimination of the fungus. This phase is followed by the activation of protein metabolism which is achieved with the production of proteasome associated with autophagy as a precursor mechanism of PCD. This work also identifies candidate genes for further functional studies and for genetic mapping and marker assisted selection.

The pathogenesis-related protein PR-4b from Theobroma cacao presents RNase activity, Ca2+ and Mg2+ dependent-DNase activity and antifungal action on Moniliophthora perniciosa

“…After the initial stage, in the resistant cacao plants, the TcPR-4b expression was observed in all the samples with a relatively high level (from 2 to 8 times higher than the control) while a gene repression was observed from 8 to 30 dai in susceptible plants (compared to the control) followed by an increase of expression from 45 to 90 dai (Figure  6). In the resistant cacao genotype, even if no macroscopic symptom were observed, some metabolic alterations have been related after inoculation of the plants by M. perniciosa [45,54,59]. Among them, H 2 O 2 production associated to calcium oxalate crystal (COC) dissolution as well as expression of genes involved in Ca 2+ dependent-signalization were observed at the initial stages after inoculation (24, 48 and 72 hai) [45,54,59].…”

“…In the resistant cacao genotype, even if no macroscopic symptom were observed, some metabolic alterations have been related after inoculation of the plants by M. perniciosa [45,54,59]. Among them, H 2 O 2 production associated to calcium oxalate crystal (COC) dissolution as well as expression of genes involved in Ca 2+ dependent-signalization were observed at the initial stages after inoculation (24, 48 and 72 hai) [45,54,59]. Moreover, a germin-like oxalate oxidase – responsible for COC dissolution – was expressed constantly in the resistant cacao genotype, making a high Ca 2+ amount available a long time after the plant has been in contact with the pathogen [54,59].…”

“…In the case of TcPR-10, this gene was related to defense responses in the final stages of the witches’ broom disease. The corresponding TcPR-10 protein also presents RNase enzymatic activity and antifungal action against M. perniciosa and Saccharomyces cerevisiae [40,45]. Here, we described another PR protein, the TcPR-4b, which was identified from a cacao pod- M. perniciosa interaction cDNA library (Ceplac project/unpublished data) and from a cacao meristem- M. perniciosa interaction library [46].…”

Genomic analyses and expression evaluation of thaumatin-like gene family in the cacao fungal pathogen Moniliophthora perniciosa

“…Leal et al [7], and Da Hora Jr. et al [8], have reported the expression of plant TLPs during the interaction between the chocolate tree Theobroma cacao and Moniliophthora perniciosa (Stahel) Aime & PhillipseMora [9], a basidiomycete hemibiotrophic pathogen that causes Witches' Broom Disease (WBD) of cacao. WBD is one of the most devastating plant diseases in the Americas, causing serious economical problems in cacao producing regions with yield losses reaching from 50% to 90% [10,11].…”

High-Resolution Transcript Profiling of the Atypical Biotrophic Interaction betweenTheobroma cacaoand the Fungal PathogenMoniliophthora perniciosa

“…Previous studies investigated cacao responses to M. perniciosa infection at the transcriptional level (Gesteira et al, 2007;Leal et al, 2007;da Hora Junior et al, 2012). However, they mainly involved comparisons between resistant and susceptible genotypes, with the aim of identifying resistance mechanisms.…”