Abstract
Sugarcane smut caused by Sporisorium scitamineum is a critical fungal disease in the sugarcane industry. However, molecular mechanistic studies of pathological response of sugarcane to S. scitamineum are scarce and preliminary. Here, transcriptome analysis of sugarcane disease induced by S. scitamineum at 24, 48 and 120 h was conducted, using an S. scitamineum-resistant and -susceptible genotype (Yacheng05-179 and “ROC”22). The reliability of Illumina data was confirmed by real-time quantitative PCR. In total, transcriptome sequencing of eight samples revealed gene annotations of 65,852 unigenes. Correlation analysis of differentially expressed genes indicated that after S. scitamineum infection, most differentially expressed genes and related metabolic pathways in both sugarcane genotypes were common, covering most biological activities. However, expression of resistance-associated genes in Yacheng05-179 (24–48 h) occurred earlier than those in “ROC”22 (48–120 h), and more transcript expressions were observed in the former, suggesting resistance specificity and early timing of these genes in non-affinity sugarcane and S. scitamineum interactions. Obtained unigenes were related to cellular components, molecular functions and biological processes. From these data, functional annotations associated with resistance were obtained, including signal transduction mechanisms, energy production and conversion, inorganic ion transport and metabolism, and defense mechanisms. Pathway enrichment analysis revealed that differentially expressed genes are involved in plant hormone signal transduction, flavonoid biosynthesis, plant-pathogen interaction, cell wall fortification pathway and other resistance-associated metabolic pathways. Disease inoculation experiments and the validation of in vitro antibacterial activity of the chitinase gene ScChi show that this sugarcane chitinase gene identified through RNA-Seq analysis is relevant to plant-pathogen interactions. In conclusion, expression data here represent the most comprehensive dataset available for sugarcane smut induced by S. scitamineum and will serve as a resource for finally unraveling the molecular mechanisms of sugarcane responses to S. scitamineum.
Highlights
Sugarcane (Saccharum officinarum) is an important sugar crop, and disease within this commodity affects cane yield and sugar content
Merged data were assembled and clustered according to similarity to 15,394 sugarcane unigene sequences downloaded from the National Center for Biotechnology Information (NCBI) website to construct the merged unigene database (Merge_Unigene) and for subsequent analyses
We found some functional annotation information associated with smut resistance which involved in signal transduction mechanisms (21 genes distributed at 24 h, 40 genes distributed at 48 h, and 26 genes distributed at 120 h), energy production and conversion (17, 27, and 32), inorganic ion transport and metabolism (10, 24, and 19), and defense mechanisms (3, 7, and 3)
Summary
Sugarcane (Saccharum officinarum) is an important sugar crop, and disease within this commodity affects cane yield and sugar content. The disease commonly manifests after infection with Sporisorium scitamineum, presenting as a black growth from the tip (‘‘smut whip’’) of the diseased sugarcane stalk. Tiller more than normal with slender stems and leaves. Smut whips grow on tillers, reducing sugarcane yield and sugar quality. Sugarcane smut has emerged as a globally important disease, and prevalence is increasing annually. It can cause a 20–50% loss in sugarcane production [2,3]. Replacing susceptible with resistant cultivars is a cost-effective measure for controlling sugarcane smut [4]
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