Two-component regulatory system (TCS) is the dominant mechanism that controls almost physiological processes of bacteria, such as nutrition assimilation, cell motility, chemotaxis, biofilm formation, quorum sensing and virulence. The intracellular informing process by a typical TCS accompany transfer of a phosphoryl group from His of a histidine kinase (HK) to Asp of a response regulator (RR). In Xanthomonas oryzae pv. oryzae (Xoo) genome, the TCS genes comprise approximately 3% of the nucleotide sequences with 58 response regulators (RRs), 32 orthodox histidine kinase (HKs) and 13 hybrid histidine kinase (HyHKs). However, there is not much understanding of RRs in Xoo except the reported RRs in Xanthomonas spp. including RpfC-RpfG, RavS-RavR, HrpG, VgrS-VgrR (also named ColS-ColR), VemR, RaxH-RaxR, and PhoQ-PhoP. Although a genome-scale mutagenesis and phenotypic characterization of TCSs were studied in Xanthomonas campestris pv. campestris ATCC 33913, there is not any genome-scale research of TCSs in Xanthomonas oryzae pv. oryzae. We have mutagenized 52 predicted RR genes in Xoo PXO99A by marker-exchange mutagenesis method and characterized the phenotype of mutants to identify RR genes involving in pathogenicity of Xoo and understand how Xoo TCSs work in given conditions. Ours investigation with the RR knock-out mutant strains have identified four novel RR genesthat are likely involved in virulence of Xoo. We have studied with these genes in molecular level to elucidate the mechanism for Xoo pathogenicity.

• Minh-Phuong Nguyen(Department of Plant Molecular Systems Biotechnology & Crop Biotech Institute, Kyung Hee University)
• Joo-Mi Yoon(Department of Plant Molecular Systems Biotechnology & Crop Biotech Institute, Kyung Hee University)
• Sang-Won Lee(Department of Plant Molecular Systems Biotechnology & Crop Biotech Institute, Kyung Hee University) Corresponding Author