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Abstract:
Witches’ broom disease of cacao is caused by Moniliophthora perniciosa. By using Micro-Tom (MT) tomato (Solanum lycopersicum) as a model system, we investigated the physiological and metabolic consequences of M. perniciosa infection to determine if symptoms result from sink establishment during infection. Infection of MT caused a reduction in root biomass and fruit yield, while decreasing leaf gas exchange and downregulating photosynthesis-related genes. The total leaf area and water potential decreased, while ABA levels, water conductance/conductivity, and ABA-related gene expression increased. Genes related to sugar metabolism and those involved in secondary cell wall deposition were upregulated upon infection, together with increased levels of sugars, fumarate, and amino acids. 14C-glucose was mobilized towards infected MT stems, but not in inoculated stems of the MT-line overexpressing CYTOKININ OXIDASE-2 (35S::AtCKX2), suggesting a role for cytokinin in establishing the sugar sink. The upregulation of genes involved in cell wall deposition and phenylpropanoid metabolism in infected MT, but not in 35S::AtCKX2 plants, suggests a cytokinin-mediated sink establishment that promotes tissue overgrowth with the increase in lignin. Possibly, M. perniciosa could benefit from the accumulation of secondary cell walls during its saprotrophic phase of infection.
