Naturally Existing Levels of Osmyb4 Gene Expression in Rice Cultivars Correlate with their Reaction to Fungal and Bacterial Pathogens

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.