Xanthomonas oryzae pv.oryzicola, the causal agent of bacterial leaf streak in the model plant rice, causing serious bacterial leaf streak (Bacterial Leaf Streak, BLS) in rice in recent years in China, possesses a conserved hrp-hrc-hpa gene cluster that encodes a type Ⅲ secretion system (T3SS) through which T3SS effectors are injected into plant cells to cause disease in susceptible host plant or trigger defenses in nonhost and resistance plant.Mutations in this cluster usually abolish the bacterial ability to cause hypersensitive response (HR) in nonhost tobacco and pathogenicity in host rice.