RNAseq based transcriptome analysis and identification of sugarcane genes expressed in response to Sporisorium scitamineum, the causal agent of smut

Author(s)

Alessandra Carolina Palhares

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2014-09-09

Examining board members

Maria Lucia Carneiro Vieira; Lilian Amorim; Gabriel Rodrigues Alves Margarido; Maria Magdalena Rossi

• Advisor: Maria Lucia Carneiro Vieira; Claudia Barros Monteiro Vitorello

Abstract

Sugarcane (Saccharum spp.) is an important crop, and hosts several pathogens, including the biotrophic fungus Sporisorium scitamineum, the causal agent of smut. The disease reduces the sugarcane crop yield and the quality of its products, and is recognized by the development of a whip-like structure, where teliospores are produced. The objective of this study was to analyze the transcriptome of sugarcane - S. scitamineum interaction and to identify differentially expressed genes from the host in response to fungal infection. Buds of the tolerant variety \'RB92-5345\' were inoculated with S. scitamineum and maintained in a greenhouse for two sampling interaction moments: 120 h after inoculation, and at the moment of the whip emission, 200 days after inoculation. Twelve libraries were constructed based on RNAseq approach. Three computational strategies were used in the mapping step and differential expression analysis of sugarcane genes: (i) STAR and DESeq, using as reference the sorghum genome; (ii) Bowtie 2 and DESeq, and (iii) CLC Genomics Workbench, using as reference the coding sequences (CDS) from sorghum. Venn diagrams were created to identify differential expressed genes that were common to the three computational strategies, thus increasing the analysis accuracy. For annotation, the BLAST2GO tool was used. We have obtained 225 million reads; out of the 185 million reads used for mapping, 66% were mapped to genes and 51% to CDS. Approximately 77% and 87% of the mapped genes and CDS respectively showed transcriptional activity (at least one read was mapped) under the experimental conditions at both interaction moments. A total of 596 and 2,148 differentially expressed genes were identified at early and late responses to the infection, respectively; it was possible to attribute function to 79% of them. Through intersectioning, 41 (early response) and 206 (late response) genes were found to be common to the three strategies. It is suggested that the plant recognizes the pathogen at the beginning of interaction period, though the fungal is able to suppress the host defense response. It is also proposed that a defense-oriented transcriptional reprogramming takes place, supporting plant development even with the disease setting. The expression of genes related to resistance, hormone pathways, and cell wall formation (as well as inhibitors of fungal proteins) suggests that the plant makes exceptional efforts to survive after 200 days of interaction. Deciphering the sugarcane transcriptome profile during the interaction with S. scitamineum, this study should contribute to a better understanding of the resistance mechanisms to the smut. (AU)

• FAPESP's process: 12/09524-0 - Molecular studies on the interaction sugarcane x Sporisorium scitamineum, the smut causal agent
• Grantee: Alessandra Carolina Palhares
• Support Opportunities: Scholarships in Brazil - Doctorate