Comparative Analysis of Sugar Metabolites and Their Transporters in Sugarcane Following Sugarcane mosaic virus (SCMV) Infection

Sugarcane mosaic virus (SCMV) is one of the major pathogens of sugarcane. SCMV infection causes dynamic changes in plant cells, including decreased photosynthetic rate, respiration, and sugar metabolism. To understand the basics of pathogenicity mechanism, we performed transcriptome and proteomics analysis in two sugarcane genotypes (Badila: susceptible to SCMV and B-48: SCMV resistant). Using Saccharum spontaneum L. genome as a reference, we identified the differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) that participate in sugar metabolism, transport of their metabolites, and Carbohydrate Activating enZYmes (CAZymes). Sequencing data revealed 287 DEGs directly or indirectly involved in sugar metabolism, transport, and storage, while 323 DEGs are associated with CAZymes. Significant upregulation of glucose, sucrose, fructose, starch, and SWEET-related transcripts was observed in the Badila after infection of SCMV. B-48 showed resistance against SCMV with a limited number of sugar transcripts up-regulation at the post-infection stage. For CAZymes, only glycosyltransferase (GT)1 and glycosyl hydrolase (GH)17 were upregulated in B-48. Regulation of DEGs was analyzed at the proteomics level as well. Starch, fructose, glucose, GT1, and GH17 transcripts were expressed at the post-translational level. We verified our transcriptomic results with proteomics and qPCR data. Comprehensively, this study proved that Badila upregulated sugar metabolizing and transporting transcripts and proteins, which enhance virus multiplication and infectionl.

Development and Evaluation of Stable Sugarcane Mosaic Virus Mild Mutants for Cross-Protection Against Infection by Severe Strain

Sugarcane mosaic virus (SCMV; genus Potyvirus) induces maize dwarf mosaic disease that has caused serious yield losses of maize in China. Cross-protection is one of the efficient strategies to fight against severe virus strains. Although many mild strains have been identified, the spontaneous mutation is one of the challenging problems affecting their application in cross-protection. In this study, we found that the substitution of cysteine (C) at positions 57 or 60 in the zinc finger-like motif of HC-Pro with alanine (A; C57A or C60A) significantly reduced its RNA silencing suppression activity and SCMV virulence. To reduce the risk of mild strains mutating to virulent ones by reverse or complementary mutations, we obtained attenuated SCMV mutants with double-mutations in the zinc finger-like and FRNK motifs of HC-Pro and evaluated their potential application in cross-protection. The results showed that the maize plants infected with FKNK/C60A double-mutant showed symptomless until 95 days post-inoculation and FKNK/C60A cross-protected plants displayed high resistance to severe SCMV strain. This study provides theoretical and material bases for the control of SCMV through cross-protection.

First Report of Sugarcane Mosaic Virus in Zea mays L. in Ukraine

Maize viral diseases especially maize dwarf mosaic disease (MDMD), which is caused by potyviruses, lead to significant crop losses worldwide. Aim. The aim of this work was to identify the causal agent of mosaic symptoms, observed on maize plants during 2018—2020 in Kyiv region. Methods. Enzyme-linked immunosorbent assay in the DAS-ELISA modification using commercial Loewe Biochemica test systems for Maize dwarf mosaic virus (MDMV), Sugarcane mosaic virus (SCMV), Wheat streak mosaic virus (WSMV) were applied to identify the causal agent of maize disease in collected samples. Transmission electron microscopy was used in order to direct viral particle visualisation. Aphids, which are natural vectors of plant viruses, were found on diseased plants. Results. Plants with typical mosaic symptoms were observed in corn crops of the Kyiv region in early June 2018. The pathogen was transmitted by mechanical inoculation to maize and sweet maize plants with the manifestation of mosaic symptoms. Electron microscopy of the sap from diseased plants revealed the presence of flexible filamentous virions 750 nm long and 13 nm in diameter, typical for the genus Potyvirus. In August, mosaic symptoms and aphids Rhopalosiphum padi were found on previously healthy plants in the same maize crop. In 2020, in the same sown area, maize plants were free of viral infection during inspection in June, but a re-inspection in September revealed mosaic symptoms on maize crop and the presence of aphids in the leaf axils. The presence of SCMV in maize samples collected in June and August/September 2018 and 2020, as well as in inoculated maize and sweet maize plants, was confirmed by ELISA using a commercial test system. The obtained data allow suggesting that Rhopalosiphum padi is a natural vector of SCMV in agrocenoses of Ukraine. It should be noted that co-infection with MDMV and WSMV in the affected plants was not detected. Conclusions. This study presents the first report of SCMV in maize in Ukraine.

Distinguishing resistances of transgenic sugarcane generated from RNA interference and pathogen‐derived resistance approaches to combating sugarcane mosaic virus

Sugarcane mosaic virus (SCMV) is a causative agent that reduces growth and productivity in sugarcane. Pathogen‐derived resistance (PDR) and RNA interference (RNAi) are the most common approaches to generating resis‐ tance against plant viruses. Two types of transgenic sugarcane have been obtained by PDR and RNAi methods using a gene‐encoding coat protein (CP) of SCMV (SCMVCp). This research aimed to distinguish resistance of the two transgenic sugarcanes in combating SCMV through artificial viral inoculation. The experiment was conducted using transgenic sugar‐ cane lines validated by PCR analysis. Insertion of gene‐encoding CP in the transgenic lines was confirmed by amplification of 702 bp of DNA fragment of SCMVCp. After viral inoculation, mosaic symptoms appeared earlier, at 21 days post inoculation (dpi) in PDR transgenic lines, but was at 26 dpi in RNAi transgenic lines. Symptom observation showed that 77.8% and 50% of the inoculated plants developed mosaic symptoms in PDR and RNAi transgenic lines, respectively. RT‐PCR analysis revealed that the nuclear inclusion protein b (Nib) gene of SCMV was amplified in the symptomatic leaves in plants classified as susceptible lines. Immunoblot analysis confirmed presence of viral CP with a molecular size of 37 kDa in the susceptible lines. Collectively, these results indicated that the RNAi approach targeting the gene for CP effectively produces more resistance against the SCMV infection in transgenic sugarcane compared to the PDR approach.