Ovarian Tumor Domain-Containing Proteases-Deubiquitylation Enzyme Gene SsCI33130 Involved in the Regulation of Mating/Filamentation and Pathogenicity in Sporisorium scitamineum

Kynurenine 3-Monooxygenase Gene SsCI51640 Is Required for Sporisorium scitamineum Mating/Filamentation by Regulating cAMP Pathway and Improving Sporidia Environmental Adaptability

Sugarcane smut is a serious disease caused by Sporisorium scitamineum, which causes significant losses to the sugar industry. It is critical to reveal the molecular pathogenic mechanism of S. scitamineum to explore a new control strategy for sugarcane smut. On the basis of transcriptome sequencing data of two S. scitamineum strains with different pathogenicity, we identified the gene, SsCI51640, which was predicted to encode kynurenine 3-monooxygenase. In this study, we obtained knockout mutants and complementary mutants of this gene and identified gene function. The results showed that the sporidial growth rate and acid production ability of knockout mutants were significantly higher and stronger than those of the wild-type and complementary mutants. The growth of knockout mutants under abiotic stress (osmotic stress and cell wall stress) was significantly inhibited. In addition, the sexual mating ability and pathogenicity of knockout mutants were significantly reduced, while this phenomenon could be restored by adding exogenous cyclic adenosine monophosphate (cAMP). It is thus speculated that the SsCI51640 gene may regulate sexual mating and pathogenicity of S. scitamineum by the cAMP signaling pathway. Moreover, the SsCI51640 gene enhanced the sporidial environmental adaptability, which promoted sexual mating and development of pathogenicity. This study provides a theoretical basis for the molecular pathogenesis of S. scitamineum.

Squalene Monooxygenase Gene SsCI80130 Regulates Sporisorium scitamineum Mating/Filamentation and Pathogenicity

Sugarcane is an important sugar crop and energy crop worldwide. Sugarcane smut caused by Sporisorium scitamineum is a serious fungal disease that occurs worldwide, seriously affecting the yield and quality of sugarcane. It is essential to reveal the molecular pathogenesis of S. scitamineum to explore a new control strategy of sugarcane smut. Based on transcriptome sequencing data of two S. scitamineum strains Ss16 and Ss47, each with a different pathogenicity, our laboratory screened out the SsCI80130 gene predicted to encode squalene monooxygenase. In this study, we obtained the knockout mutants (ΔSs80130+ and ΔSs80130−) and complementary mutants (COM80130+ and COM80130−) of this gene by the polyethylene glycol-mediated (PEG-mediated) protoplast transformation technology, and then performed a functional analysis of the gene. The results showed that the deletion of the SsCI80130 gene resulted in the increased content of squalene (substrate for squalene monooxygenase) and decreased content of ergosterol (the final product of the ergosterol synthesis pathway) in S. scitamineum. Meanwhile, the sporidial growth rate of the knockout mutants was significantly slower than that of the wild type and complementary mutants; under cell-wall stress or oxidative stress, the growth of the knockout mutants was significantly inhibited. In addition, the sexual mating ability and pathogenicity of knockout mutants were significantly weakened, while the sexual mating ability could be restored by adding exogenous small-molecular signal substance cAMP (cyclic adenosine monophosphate) or tryptophol. It is speculated that the SsCI80130 gene was involved in the ergosterol biosynthesis in S. scitamineum and played an important role in the sporidial growth, stress response to different abiotic stresses (including cell wall stress and oxidative stress), sexual mating/filamentation and pathogenicity. Moreover, the SsCI80130 gene may affect the sexual mating and pathogenicity of S. scitamineum by regulating the ergosterol synthesis and the synthesis of the small-molecular signal substance cAMP or tryptophol required for sexual mating. This study reveals for the first time that the gene encoding squalene monooxygenase is involved in regulating the sexual mating and pathogenicity of S. scitamineum, providing a basis for the molecular pathogenic mechanism of S. scitamineum.

Sugarcane Smut: Current Knowledge and the Way Forward for Management

Whip smut of sugarcane is the most serious and widely spread disease of sugarcane and causes a significant reduction in cane quantity and quality. The severity of this disease often depends on the pathogen races, environmental conditions, cultivar genotype and the interaction among these three factors. Under optimum climatic conditions, this disease has the potential to cause total crop failure. Resistance screening is an ongoing process due to the variability among smut pathogen isolates. Multiple races and mutation ability of smut pathogen makes the breeding task more complex. A number of studies on various aspects of the disease epidemiology and management have been published. Due to many overlapping characteristics within the species complex, there is a dearth of information on early detection and strategies to control the smut pathogen. Furthermore, there is a need to coordinate these findings to expedite its research and control. In this paper, we summarize the disease etiology, especially disease impact on the qualitative and quantitative parameters of sugarcane. We also gathered research progress on molecular-based detection and available information on genetic variability in S.scitamineum. The research on the set of management options needed to effectively cope with the disease are reviewed herein. The present review is expected to be helpful for the further investigation on smut resistance in sugarcane.