Involvement of NPR1 and Some Pathogenesis-Related Genes in Challenging with Bacterial Rice Blight caused by Xanthomonas Oryzae pv. Oryzae

Bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae is one of the destructive diseases of this product in different parts of the world. Due to the inefficiency of chemical management and environmental contamination, the use of resistant cultivars is one of the most effective and economical ways to manage this disease. In addition, the lack of sufficient information to understand the mechanism of resistance in Iranian rice and in resistant cultivars, show that molecular evaluation of genes expression in sensitive and resistant cultivars in interaction with the disease agent, is needed.

In this study, the expression pattern of NPR1 and several PR genes (including PR1b, PR3 and PR5) in different time courses after inoculation was evaluated. Quantitative Real time PCR was performed in resistant and sensitive populations (Khazar and Tarom) to bacterial blight.

In the study of gene expression, the trend of increasing gene expression in the Khazar resistant cultivar compared to the sensitive cultivar was confirmed from the early hours after inoculation. The maximum expression of NPR1 gene in resistant cultivar was at 12 hours after infection (hai). In the case of pathogen-related genes expression, the activity of PR1b gene at 72 hai in resistant cultivar was 11.2 fold and in 96 hai was 25.7 fold higher than sensitive cultivar. High expression levels of PR3 gene at 12 and 48 hai in resistant cultivar was evaluated 38 and 10.4 times higher than sensitive Tarom local cultivar, respectively. The expression level of PR5 gene in resistant Khazar cultivar at 48, 72 and 96 hours was 4.1, 7.6 and 22 fold higher than the sensitive cultivar, respectively.

Since the accumulation of mRNA transcripts and increased activity of these genes is an important indicator of the development of a defense response in interaction with the disease agent, the activity of these genes indicates the presence of resistance potential in the Iranian Khazar cultivar is important against this disease. In general, activation of different pathways of systemic resistance (SAR) and induction of resistance genes in the emergence of resistance of Khazar cultivar compared to Tarom susceptible cultivar, is part of the defense mechanism of rice against Xoo. The results of this research along with the evaluation of the gene expression can promise the proper efficiency of the Khazar variety during the epidemic of the mentioned disease or a potential for transferring the resistance gene to sensitive cultivars in integrated management or pyramidal resistance.