Evaluation of the contribution of plant hormones in the interaction Moniliophthora perniciosa x Solanum lycopersicum

Author(s)

Juliana Deganello

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB)
• Defense date: 2012-08-24

Examining board members

Antonio Vargas de Oliveira Figueira; Juliana de Freitas Astúa; Victor Alexandre Vitorello

• Advisor: Antonio Vargas de Oliveira Figueira

Abstract

Witches\' broom disease is a major disease of cacao (Theobroma cacao), caused by the basidiomycete Moniliophthora perniciosa, characterized by symptoms, such as tissue swelling and induction of lateral buds in infected branches. Cacao resistance mechanisms against M. perniciosa remain unknown, and the long lifecycle of such species impairs the study of the interaction. Moniliophthora perniciosa S-biotype- isolates infect tomato (Solanum lycopersicum), and the miniature cultivar \'Micro-Tom\' (MT) is a potential genetic model for the study of plant and pathogen interaction. Evaluation of this model started with the characterization of symptoms in MT plants inoculated with S-biotype isolates. Symptoms evaluated were stem swelling and the development of lateral broom. Through histological characterization of the interaction by scanning electron microscopy, it was possible to observe the preferential germination of basidiospores in the base of trichomes, with penetration points through wounds or directly through the epidermis. Increase in cellular volume in infected tissues was observed by light microscopy, and the colonization of the intercellular region by the fungus was detected through transmission electron microscopy, with the formation of an extracellular matrix involving the hypha. The contribution of plant hormones during pathogenesis was evaluated through the use of mutants and transgenic plants on the \'Micro-Tom\' background with alterations in hormonal biosynthetic pathways or perception/signaling. The hormonal classes and genotypes evaluated were for brassinosteroids (curl3), auxin (diageotropica), ethylene (epinastic and Never ripe), abiscisic acid (notabilis); gibberellin (procera); jasmonic acid (jasmonic acid insensitive 1e prosistemina); cytokinins (CKX2) and silicic acid (NahG). The genotypes epinastic, notabilis, procera e jasmonic acid insensitive 1 behaved as being more susceptible to M. perniciosa infection when compared to MT, while the remaining mutants were less susceptible, suggesting that the reduction in susceptibility to M. perniciosa might be related to the increase in jasmonate levels (JA), in the opposite to the levels of salicylate, which seems to increase together with the increase of symptomatic plants. Cross infection with biotype-C isolates was characterized in MT, hormonal mutants and transgenic plants, however typical symptoms of the disease were not observed in any of the genotypes inoculated. Genes involved in plant response and defense were evaluated for expression levels by RT-qPCR in the interaction between M. perniciosa S-and C-biotype with MT . After inoculation with S-biotype, the largest number of genes were up-regulated 48 h after inoculation, followed by a peak at the 120 h sampling. On the other hand, for C-biotype inoculation, gene induction started 48 h after inoculation, but the largest number of transcripts was detected after 72 hours. Hormonal mutants (jasmonic acid insensitive 1 and curl3) and transgenic plants (prosistemina and NahG) were also assessed for expression levels of genes related to plant response and defense. Both transgenic genotypes which behaved less susceptible to the disease showed up-regulation of a proteinase inhibitor typically signaled by JA pathway, corroborating the hypothesis that the reduction of the number of plants infected by M. perniciosa may be related to the jasmonic acid pathway (AU)

• FAPESP's process: 09/12785-7 - Evaluation of the contribution of plant hormones in the interaction Moniliophthora perniciosa - Solanum lycopersicum
• Grantee: Juliana Deganello
• Support Opportunities: Scholarships in Brazil - Master