Molecular Regulation Of Xrg1 On Xa21-Mediated Disease Resistance In Rice

Rice, as one of the most important crops, feeds over 50% population in the world. However, grain yield and quality in rice were seriously declined due to the attack of rice bacterial blight, which is one of the major rice diseases. Therefore, studying the molecular mechanism of rice resistance to bacterial blight could provide an important theoretical basis for the application of rice bacterial blight resistance, thus it is of great significance to ensure food security.To search the candidates associated with the bacterial blight resistance, we analyzed the relevant data in the database of rice gene expression microarray (http://www.ricearray.org). We found one gene induced within the infection of Xanthomonas oryzae pv. Oryzae (Xoo), which was named as Xoo-responsive gene 1 (Xrgl). To investigate whether Xrgl is involved in the resistance to bacterial blight, we study its biological function using genetics and molecular biology and the following results are obtained:1. XRG1 is an expressed protein containing a P4Hc domain. Previous studies showed that the protein possessing the P4Hc domain were associated with biotic and abiotic stress in Arabidopsis thaliana. Therefore, we suggest that the XRG1 might play roles in response to plant immunity.2. The expression pattern of Xrgl was determined using qRT-PCR. The Xrgl is expressed in the various tissues, and highly expressed in stems and leaves especially. More importantly, the expression level of the Xrg1 was gradually increased within the development of rice.3. To determine whether the Xrgl modulate Xa21-mediated disease resistance, we silenced the Xrgl in Xa21-Kittake background using the RNAi approach. We analyzed the expression level of Xrgl in transgenic plants through qRT-PCR ways and obtained some stability Ts homozygous transgenic plants with reduced transcripts level of Xrgl.4. Then we measured the lesion length and bacterium numbers at Od,7d and 14d post inoculation with the strain Xoo (PXO99). The lesion length of X-Xrg1Ri plants was longer than Xa21-Kitaake plants, but shorter than Kitaake. These results indicated that the Xrgl regulated Xa21-mediated resistance to Xoo.5. We performed rice leaf protoplast transfection assay to investigate the subcellular localization of XRG1 and found that XRG1-GFP was located in the nucleus.6. To determine whether the XRG1 interacts with XA21. we performed yeast-two hybrid assays. The results showed that there was no direct interaction between XRG1 and XA21. suggesting that XRG1 might not physically interact with XA21 directly to regulate Xa27-mediated immunity.In summary, we suggested that Xrgl might indirectly regulated Xa21-mediated immunity in rice.