Abstract

Smut caused by biotrophic fungus Sporisorium scitamineum is a major disease of cultivated sugarcane that can cause considerable yield losses. It has been suggested in literature that there are at least two types of resistance mechanisms in sugarcane plants: an external resistance, due to chemical or physical barriers in the sugarcane bud, and an internal resistance governed by the interaction of plant and fungus within the plant tissue. Detailed molecular studies interrogating these two different resistance mechanisms in sugarcane are scarce. Here, we use light microscopy and global expression profiling with RNA-seq to investigate these mechanisms in sugarcane cultivar CP74-2005, a cultivar that possibly possesses both internal and external defence mechanisms. A total of 861 differentially expressed genes (DEGs) were identified in a comparison between infected and non-infected buds at 48 hours post-inoculation (hpi), with 457 (53%) genes successfully annotated using BLAST2GO software. This includes genes involved in the phenylpropanoid pathway, cell wall biosynthesis, plant hormone signal transduction and disease resistance genes. Finally, the expression of 13 DEGs with putative roles in S. scitamineum resistance were confirmed by quantitative real-time reverse transcription PCR (qRT-PCR) analysis, and the results were consistent with the RNA-seq data. These results highlight that the early sugarcane response to S. scitamineum infection is complex and many of the disease response genes are attenuated in sugarcane cultivar CP74-2005, while others, like genes involved in the phenylpropanoid pathway, are induced. This may point to the role of the different disease resistance mechanisms that operate in cultivars such as CP74-2005, whereby the early response is dominated by external mechanisms and then as the infection progresses, the internal mechanisms are switched on. Identification of genes underlying resistance in sugarcane will increase our knowledge of the sugarcane-S. scitamineum interaction and facilitate the introgression of new resistance genes into commercial sugarcane cultivars.

Highlights

  • Smut caused by a fungus Sporisorium scitamineum (Syd.) M

  • An important component of our study is to determine the type of resistance that exists in sugarcane varieties as external resistance can be overcome by physical damage to the bud

  • It has been found that ratooning increases the susceptibility of the sugarcane plant to smut and ratoon crops suffer a higher degree of infection than plant crops [59]

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Summary

Introduction

Smut caused by a fungus Sporisorium scitamineum (Syd.) M. (formerly called Ustilago scitaminea) [1], is a major disease of sugarcane worldwide that can cause considerable yield losses if susceptible varieties are planted [2, 3]. The most effective management of smut is through the propagation of smut-resistant varieties [4]. In Australia in 2006, soon after smut was found in Queensland, a major program was undertaken to screen sugarcane clones from various stages of selection programs, parents and foreign varieties with the ultimate aim of replacing susceptible varieties grown in Australia with smutresistant varieties [5]. To improve breeding for such varieties, the need exists for knowledge of resistance mechanisms

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