Study of miR156-targeted SPL/SBP-box genes in the interaction between the atypical pathogen Moniliophthora perniciosa and Solanum lycopersicum cv. Micro-tom

Author(s)

Rafael Monteiro do Carmo

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB)
• Defense date: 2021-09-14

Examining board members

Eder Marques da Silva; Luciano Freschi; Ana Karla Machado Wood

• Advisor: Lazaro Eustaquio Pereira Peres; Eder Marques da Silva

Abstract

Witches\' Broom Disease (WBD), caused by the hemibiotrophic basidiomycete Moniliophthora perniciosa [syn. Crinipellis perniciosa (Stahel) Singer; Marasmiaceae s.l.], is the most significant disease of cacao (Theobroma cacao) in Brazil. M. perniciosa can infect a variety of hosts, allowing classification into 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 solanaceous plants such as tomato (Solanum lycopersicum). Our group has demonstrated that the tomato cultivar Micro-Tom (MT) is a suitable model for studying the biotrophic phase of the interaction with M. perniciosa. Mainly because the pathogen induces in MT symptoms of hypertrophy, stem hyperplasia, and uncontrolled branching, forming green brooms (symptoms characteristic of C-biotype infected T. cacao). However, the transition to the necrotrophic stage of the disease with the formation of basidiocarps has never been reported in tomato. Additionally, our group showed that cytokinins (CKs) are important for the development and progression of symptoms. Recently, the repression of proteins from the SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL/SBP-box) family of transcription factors has been shown to be part of the infection strategy of pathogens causing WBD-like diseases. Such transcription factors are plant specific and play essential functions for plant development (e.g. branching) in addition to acting in response to abiotic and biotic stresses. Furthermore, some members of this family have been described to interfere negatively with CK signaling. Interestingly, transgenic MT plants with low levels of SPL/SBPs, due to the overexpression of microRNA156 (156-OE, which down-regulates SPL/SBPs), have some phenotypic characteristics that resemble M. perniciosa-infected MT plants. Such as increased branching and number of locules in the fruits. Looking at our group previous mRNA-seq data from inoculated MT plants, we observed that the repression of SPL/SBPs is part of the M. perniciosa infection strategy. Thus, we investigated whether the repression of such proteins has an impact on susceptibility by inoculating 156-OE plants. Such plants showed not only more symptoms, but also increased severity of symptoms, greater pathogen colonization, and, for the first time in a tomato genotype, we noticed the transition to the necrotrophic stage, producing basidiocarps. Orthologs of the tomato SlSBP15 gene (e.g. arabidopsis AtSPL9) participate in the immune response and also in CK signaling. Thus, we inoculated plants that overexpress a version of this protein resistant to the downregulation by the microRNA156 (rSBP15-OE). These plants developed fewer symptoms, and symptoms developed were milder. Furthermore, they demonstrated less pathogen colonization than MT. Consistently, rSBP15-OE plants show induced defense and CK-degradation genes, which is possibly responsible for the reduction of symptoms. Meanwhile, 156-OE plants have repressed defense genes and induced CK-synthesis genes, which may be favoring the pathogen. Thus, this gene is a potential candidate for further studies involving resistance to M. perniciosa, with potential applications in cacao improvement (AU)

• FAPESP's process: 19/12188-0 - Evaluation of the orchestrated pathways of miR156 in the interaction between Moniliophthora perniciosa and Solanum lycopersicum: consequences for pathogenesis and susceptibility
• Grantee: Rafael Monteiro Do Carmo
• Support Opportunities: Scholarships in Brazil - Master