Characterizing rice lesion mimic mutants and identifying a mutant with broad-spectrum resistance to rice blast and bacterial blight

Many plant mutants develop spontaneous lesions that resemble disease sympto ms in the absence of pathogen attack. In several pathosystems, lesion mimic mutations have been shown to be involved in programmed cell death, which i n some instances leads to enhanced disease resistance to multiple pathogens . We investigated the relationship between spontaneous cell death and disea se resistance in rice with nine mutants with a range of lesion mimic phenot ypes. All nine mutations are controlled by recessive genes and some of thes e mutants have stunted growth and other abnormal characteristics. The lesio n mimics that appeared on the leaves of these mutants were caused by cell d eath as measured by trypan blue staining. Activation of six defense-related genes was observed in most of the mutants when the mimic lesions developed , Four mutants exhibited significant enhanced resistance to rice blast. One of the mutants, spill, confers non-race-specific resistance not only to bl ast but also to bacterial blight. The level of resistance In the spill muta nt to the two pathogens correlates with the defense-related gene expression and lesion development on the leaves. The results suggest that some lesion mimic mutations in rice may be involved in disease resistance, and cloning of these genes may provide a clue to developing broad-spectrum resistance to diverse pathogens.