The reaction of IR 50, TRY 3, and IR 36 cultivars of rice to R. solani challenge, the causal agent of sheath blight, and its toxic metabolite was studied. Differential response of these cultivars to the pathogen and/or toxin inoculation was observed in detached leaf sheaths and greenhouse-grown plants. The observations were based on disease scoring, electrolyte leakage, and also microscopic views of infection cushions. The Osmyb4 gene expression was studied in the tissues from all these experiments and a correlation between the level of expression and disease response of the varieties was found at least in some experiments. The mechanisms regulated by Osmyb4 might have a lower but significant contribution to the tolerance of rice cultivars to sheath blight.

Pooja Raghav

VIT School of Law

Chennai Campus

Babu S

Department of Biotechnology

School of Bio Sciences and Technology

Vellore Campus

Fulltext

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Responses of rice to Rhizoctonia solani and its toxic metabolite in relation to expression of Osmyb4 transcription factor

Plant Protection Science

Main conclusion: Rice sheath blight research should prioritise optimising biological control approaches, identification of resistance gene mechanisms and application in genetic improvement and smart farming for early disease detection. Abstract: Rice sheath blight, caused by Rhizoctonia solani AG1-1A, is one of the most devasting diseases of the crop. To move forward with effective crop protection against sheath blight, it is important to review the published information related to pathogenicity and disease management and to determine areas of research that require deeper study. While progress has been made in the identification of pathogenesis-related genes both in rice and in the pathogen, the mechanisms remain unclear. Research related to disease management practices has addressed the use of agronomic practices, chemical control, biological control and genetic improvement: Optimising nitrogen fertiliser use in conjunction with plant spacing can reduce spread of infection while smart agriculture technologies such as crop monitoring with Unmanned Aerial Systems assist in early detection and management of sheath blight disease. Replacing older fungicides with natural fungicides and use of biological agents can provide effective sheath blight control, also minimising environmental impact. Genetic approaches that show promise for the control of sheath blight include treatment with exogenous dsRNA to silence pathogen gene expression, genome editing to develop rice lines with lower susceptibility to sheath blight and development of transgenic rice lines overexpressing or silencing pathogenesis related genes. The main challenges that were identified for effective crop protection against sheath blight are the adaptive flexibility of the pathogen, lack of resistant rice varieties, abscence of single resistance genes for use in breeding and low access of farmers to awareness programmes for optimal management practices. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.

Planta

Sheath blight of rice: a review and identification of priorities for future research

The promoter regions (1. kb upstream sequences) of 45,836 annotated genes of rice were analyzed for the presence of OsMYB4 binding sites using a Perl program algorithm. Based on the homotypic clustering concept, 113 promoters were found to have more than 4 binding site motifs. Among the downstream genes of these promoters, five genes which are known to have a role in disease resistance were selected and the binding capacity of OsMYB4 protein in the promoter regions was analyzed by docking studies. Expression level of these genes was analyzed by RT-PCR in Rhizoctonia solani infected rice seedlings. Upon pathogen challenge, higher expression of aminotransferase, ankyrin and WRKY 12 genes was observed corresponding to higher expression of Osmyb4. Over-expression of Osmyb4 cDNA in rice leaf tissues by agro-infection failed to result in similar over-expression of aminotransferase, ankyrin and WRKY 12 as expected. Although the role of OsMYB4 in sheath blight resistance was found to be definitive based on our initial results, artificial over-expression of this TF was observed to be insufficient in regulating the disease resistance related genes. © 2015 Elsevier B.V.

Gene

Homotypic clustering of OsMYB4 binding site motifs in promoters of the rice genome and cellular-level implications on sheath blight disease resistance

Accumulating functional genomic data in rice are unveiling the role of regulatory genes and their significance in modulating responses to complex traits like stress tolerance. Rice Osmyb4 is one such gene coding for transcription factor, and the homologous and heterologous ectopic expression has proved increased tolerance to several abiotic stress and few biotic stresses in plants. Nevertheless, the role of this gene in rice plants for disease resistance has not been studied. We attempted to study the correlation of existing bottom-line expression of this gene in selected rice cultivars and their reaction to artificial challenge with the sheath blight pathogen (Rhizoctonia solani) and bacterial leaf blight pathogen (Xanthomonas oryzae pv. oryzae). The study consisted of artificial inoculation of the pathogens and scoring for disease in selected rice cultivars and amplification of Osmyb4 transcripts by a simple reverse transcription PCR. Inoculation studies revealed a higher disease index in cv. IR 50 and lower disease in cvs TRY 3 and IR 36. Reverse transcription PCR in healthy plants revealed significantly higher constitutive expression of this gene in cvs TRY 3 and IR 36 which was not found in IR 50. However, expression of this gene in cv. IR 50 was found to be cold-inducible. The natural expression level of Osmyb4 in disease-resistant rice varieties provides molecular evidences for their possible role in regulating disease resistance. © 2013 Blackwell Verlag GmbH.

Journal of Phytopathology

Naturally Existing Levels ofOsmyb4 Gene Expression in Rice Cultivars Correlate with their Reaction to Fungal and Bacterial Pathogens

Biologia plantarum

The OsMyb4 gene family: stress response and transcriptional auto-regulation mechanisms

Nature Communications

The evolution and pathogenic mechanisms of the rice sheath blight pathogen

Journal	Plant Protection Science
Publisher	Czech Academy of Agricultural Sciences
ISSN	1212-2580
Open Access	Yes