Functional Analysis Of Rice Bacterial Blight Disease Resistance Gene X?25

Bacterial blight,caused by Xanthomonas oryzae pv.oryzae?Xoo?,is one of most harmful diseases of rice in worldwide,and it is economical and effective to utilize the major disease resistance genes in rice to confront with Xoo.The recessive major disease resistance gene x?25 mediates race-specific resistance to Xoo strain PXO339,the expression of its dominant allele X?25 can be induced by PXO339 specifically.x?25 localizes on the centromere region of chromosome 12.xa13 and x?25 are both members of MtN3/saliva/SWEET family and x?25 protein is a membrane protein.x?25and X?25 genes encode proteins with 3 amino acid deletions and 5 amino acid substitutions and comparative analysis of the promoter regions of x?25 and X?25 show seven polymorphic sites.It is not quite clear about the molecular mechanism of x?25-mediated resistance yet.Here it is showed that constitutive expression of X?25 or x?25 in the resistant rice line Zhonghua 11 have no effect on PXO339 infection,and retain the resistance.Meanwhile,suppressing the expression of X?25 in the susceptible rice line IR24 and x?25 in the resistant rice line Zhonghua 11 both enhance rice resistant to PXO339.It is shown that the enhanced resistance cosegregated with suppression of x?25 or X?25 in T₁ families.On the other hand,the promoter of X?25 is used to regulate the expression of x?25 in the Zhonghua 11 background,and the positive transgenic plants are susceptible to PXO339and it is shown that the enhanced susceptibility cosegregated with presence of transgene in T₁ families.Compareing the corresponding regions of x?25/X?25 promoter from different variteis with the RVD?repeat-variable diresidue?of PthXo2 which is the TAL?transcription activator-like?effector of PXO339,and it is found that the RVD of PthXo2can match with the X?25 promoter from Zhenshan 97 and IR24.However,the corresponding regions of x?25 promoter from different varieties are the same and can not match with RVDs of PthXo2 because of one adenine residue deletion.Therefore,PthXo2can bind to the X?25 promoter to activate the expression of X?25.Paraffin section shows that the expression of X?25 and x?25 genes concentrates in vascular tissues,where is the path of the bacterial blight pathogen infection.