Abstract
Sheath blight disease is caused by a necrotrophic fungal pathogen Rhizoctonia solani and it continues to be a challenge for sustainable rice cultivation. In this study, we adopted a multi-pronged approach to understand the intricacies of rice undergoing susceptible interactions with R. solani. Extensive anatomical alteration, chloroplast localized ROS, deformed chloroplast ultrastructure along with decreased photosynthetic efficiency were observed in infected tissue. GC-MS based metabolite profiling revealed accumulation of glycolysis and TCA cycle intermediates, suggesting enhanced respiration. Several aromatic and aliphatic amino acids along with phenylpropanoid intermediates were also accumulated, suggesting induction of secondary metabolism during pathogenesis. Furthermore, alterations in carbon metabolism along with perturbation of hormonal signalling were highlighted in this study. The gene expression analysis including RNAseq profiling reinforced observed metabolic alterations in the infected tissues. In conclusion, the present study unravels key events associated during susceptible rice-R. solani interactions and identifies metabolites and transcripts that are accumulated in infected tissues.
Highlights
The sheath blight disease is one of the major diseases of rice and is reported from almost all rice cultivating countries in the world
We had previously reported that a R. solani strain BRS1 belonging to AG1-IA anastomosis group causes characteristic sheath blight disease symptoms (i.e elliptical brown necrotic lesion) on different rice cultivars i.e Oryza sativa ssp. indica (PB1 and TETEP) and O. sativa ssp. japonica (TP309)[19]
To understand anatomical changes imparted by R. solani, the transverse section (T.S) of rice sheaths were studied through histological staining
Summary
Dynamics of R. solani colonization during susceptible interaction in rice. We had previously reported that a R. solani strain BRS1 belonging to AG1-IA anastomosis group causes characteristic sheath blight disease symptoms (i.e elliptical brown necrotic lesion) on different rice cultivars i.e Oryza sativa ssp. indica (PB1 and TETEP) and O. sativa ssp. japonica (TP309)[19]. To understand metabolic changes that regulate physiological alterations in rice observed during 1dpi and 3dpi of R. solani infection, metabolome analysis was performed using GC-MS (Gas chromatography-mass spectrometry). Based upon the abundance of related metabolites it seems that respiratory processes are enhanced in R. solani infected rice sheaths at 3dpi (Fig. 5). To correlate the observed metabolic changes with that of transcriptional alterations, we carried out RNAseq analysis on susceptible rice genotypes (PB1 and TP309) to identify common differentially regulated genes, during transition from 1dpi to 3dpi of R. solani pathogenesis. The pathogenesis marked an increase in carbohydrate metabolism in the infected tissues (Table S3) In this regard, transcripts encoding invertase (beta-fructofuranosidase; putatively involved in breakdown of sucrose into hexoses) along with biosynthetic genes of sugars like raffinose, trehalose and myo-inositol were upregulated. Metabolite Sugar Glucopyranose Hexopyranose Galactose Maltose Sucrose D-Fructose D-Turanose D-Glucose 4-Ketoglucose/D-Glucosone Organic acids Pyruvic Acid cis-Aconitate Cyanuric acid Isobutyric acid Acetohydroximic acid Oxalic Acid Succinic acid Erythronic acid Lactic acid Thiobarbituric Acid 4-Biphenylcarboxylic acid Salicylic acid Sinapic Acid Malate Dihydroxybenzoic acid D-Glucuronic acid Talonic Acid Fatty acids α-Linolenic acid Palmitic acid Fumaric acid Phytol Amino acids Tyrosine L-Asparagine L-Proline Phenylalanine I-Aspartic Acid I-Valine γ-Aminobutyric acid Serine L-Valine L-Isoleucine L-Threonine L-Aspartic Acid Sugar alcohols D-Myo-Inisitol D-Glucitol 1,4-Butanediol Ethanolamine Myo-Inositol Glycerol 3-phosphate Others Dopamine Phosphoric acid
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