| 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 xα25 mediates race-specific resistance to Xoo strain PXO339,the expression of its dominant allele Xα25 can be induced by PXO339 specifically.xα25 localizes on the centromere region of chromosome 12.xa13 and xα25 are both members of MtN3/saliva/SWEET family and xα25 protein is a membrane protein.xα25and Xα25 genes encode proteins with 3 amino acid deletions and 5 amino acid substitutions and comparative analysis of the promoter regions of xα25 and Xα25 show seven polymorphic sites.It is not quite clear about the molecular mechanism of xα25-mediated resistance yet.Here it is showed that constitutive expression of Xα25 or xα25 in the resistant rice line Zhonghua 11 have no effect on PXO339 infection,and retain the resistance.Meanwhile,suppressing the expression of Xα25 in the susceptible rice line IR24 and xα25 in the resistant rice line Zhonghua 11 both enhance rice resistant to PXO339.It is shown that the enhanced resistance cosegregated with suppression of xα25 or Xα25 in T1 families.On the other hand,the promoter of Xα25 is used to regulate the expression of xα25 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 xα25/Xα25 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 Xα25 promoter from Zhenshan 97 and IR24.However,the corresponding regions of xα25 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 Xα25 promoter to activate the expression of Xα25.Paraffin section shows that the expression of Xα25 and xα25 genes concentrates in vascular tissues,where is the path of the bacterial blight pathogen infection. |
