The role of abscisic acid in modulating defense in \'Micro-Tom\' tomato against pathogens of contrasting lifestyle through transcriptional and post-transcriptional regulation

Author(s)

Jamille Santos da Silva

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2018-07-05

Examining board members

Antonio Vargas de Oliveira Figueira; Ronaldo José Durigan Dalio; Gabriel Rodrigues Alves Margarido; Lazaro Eustaquio Pereira Peres

• Advisor: Antonio Vargas de Oliveira Figueira

Abstract

Plant pathogens are often classified as biotrophic, necrotrophic or hemibiotrophic according to their mechanism of infection and lifestyle and, consequently, distinct host responses are activated in each case. Plant responses to pathogens are known to be regulated by plant hormones. Classically, salicylic acid (SA) signaling is required for resistance to biotrophic pathogens, whereas the combination of jasmonic acid (JA) and ethylene (ET) are required for necrotrophic resistance. In order to identify mutant and/or hormonal transgenic plants that showed differential response to infection by the necrotrophic pathogens Sclerotinia sclerotiorum and biotrophic Oidium neolycopersici, an experiment was carried out with nine mutants and hormonal transgenic tomato plants together with the \'MT\' control. In this screen, the sitiens mutant, with reduced levels of abscisic acid (ABA), presented greater susceptibility to the necrotrophic fungus and partial resistance to the biotrophic fungus in comparison to \'MT\'. Further evidence of the participation of ABA in these interactions was given by the fact that ABA contents increased in leaves of plants inoculated with both pathogens, GUS expression increased in the transgenic RD29B :: GUS whose promoter is responsive to ABA, and resistance was modulated by the exogenous application of 100 μM ABA or 2 μM fluridone in \'MT\', sitiens and the sp12 mutant (high levels of ABA). The objective of this work was to investigate the role of the ABA biosynthetic pathway in the modulation of the ascorbate-glutathione cycle of antioxidation and H2O2 removal, and the role of ABA in altering the transcriptional and protein profile in tomato leaves in response to infection by S. sclerotiorum or O. neolycopersici. sitiens presents high levels of H2O2 in the apoplast, which appears to result in programmed cell death (PCD). The presence of this mutation interrupts the ABA biosynthesis pathway, with a probable accumulation of intermediates, with the use of ascorbate by the enzyme violaxanthin de-epoxidase (VDE) in the chloroplast. Thus, this ascorbate is not transported to the apoplast to remove H2O2, promoting the accumulation of H2O2 and the consequent induction of PCD. In \'MT\' inoculated with S. sclerotiorum, the analysis of differential gene expression by RNA-seq revealed the enrichment of terms associated with groups of induced genes related to mechanisms of autophagy. Autophagy is a distinct type of PCD and is a survival strategy to prevent extensive cell death, resulting in increased resistance to necrotrophic pathogens, as observed in \'MT\'. Proteomic analysis showed that \'MT\' presented a greater relative abundance of proteins related to pathogenesis when inoculated with S. sclerotiorum. These proteins are related to JA and ET signaling pathways, secondary metabolites and cell wall degradation of fungi, conferring greater resistance to \'MT\'. In the interaction with O. neolycopersici, increased induction of resistance genes was observed in sitiens and no enrichment of terms linked to groups of autophagy genes in \'MT\' was detected. On the other hand, protein analysis revealed the participation of an endochitinase in sitiens with a presumed role in the partial resistance to this biotrophic pathogen. In conclusion, the ABA biosynthetic pathway can modify the H2O2 removal capacity and ABA can induce distinct forms of cell death and regulate the expression of resistance genes. (AU)

• FAPESP's process: 15/00060-9 - Evaluation of the role of plant hormones involved in differential response of tomato cv. Micro-Tom to fungi of genus Alternaria and Oidium through the change of transcripts
• Grantee: Jamille Santos da Silva
• Support Opportunities: Scholarships in Brazil - Doctorate