A dynamic degradome landscape on miRNAs and their predicted targets in sugarcane caused by Sporisorium scitamineum stress

Abstract

Background: Sugarcane smut is a fungal disease caused by Sporisorium scitamineum. Cultivation of smut-resistant sugarcane varieties is the most effective way to control this disease. The interaction between sugarcane and S. scitamineum is a complex network system. However, to date, there is no report on the identification of microRNA (miRNA) target genes of sugarcane in response to smut pathogen infection by degradome technology. Results: TaqMan qRT-PCR detection and enzyme activity determination showed that S. scitamineum rapidly proliferated and incurred significant enzyme activity changes in the reactive oxygen species metabolic pathway and phenylpropanoid metabolic pathway at 2 d and 5 d after inoculation, which was the best time points to study target gene degradation during sugarcane and S. scitamineum interaction. A total of 122.33 Mb of raw data was obtained from degradome sequencing analysis of YC05-179 (smut-resistant) and ROC22 (smut-susceptible) after inoculation. The Q30 of each sample was > 93%, and the sequence used for degradation site analysis exactly matched the sugarcane reference sequence. A total of 309 target genes were predicted in sugarcane, corresponding to 97 known miRNAs and 112 novel miRNAs, and 337 degradation sites, suggesting that miRNAs can efficiently direct cleavage at multiple sites in the predicted target mRNAs. Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that the predicted target genes were involved in various regulatory processes, such as signal transduction mechanisms, inorganic ion transport and metabolism, defense mechanisms, translation, posttranslational modifications, energy production and conversion, and glycerolipid metabolism. qRT-PCR analysis of the expression level of 13 predicted target genes and their corresponding miRNAs revealed that there was no obvious negative regulatory relationship between miRNAs and their target genes. In addition, a number of putative resistance-related target genes regulated by miRNA-mediated cleavage were accumulated in sugarcane during S. scitamineum infection, suggesting that feedback regulation of miRNAs may be involved in the response of sugarcane to S. scitamineum infection. Conclusions: This study elucidates the underlying response of sugarcane to S. scitamineum infection, and also provides a resource for miRNAs and their predicted target genes for smut resistance improvement in sugarcane.