Cloning And Characterization Of Hrc V Gene From Xanthomonas Oryzae Pv.oryzae Chinese Strain 13751 And Evaluation Of Protection Of Rice From Bacterial Blight With The HrcV Deletion Mutant Of 13751

One DNA fragment ca.375 bp in length was amplified from the genomic DNA of Xanthomonas oryzae pv.oryzae (hereafter Xoo) Chinese strain 13751 with a pair of primers designed according to the conserved sequences of hrcV (hrpC2) of Xanthomonas campestris pv.vesicatoria(hereafter Xcv) and hrcV(hrpO) of Ralstonia soianacearum (hereafterRS) .The PCR product was confirmed by sequencing to be 96%.. 84% homology with hrcV gene of Xcv and hrcV gene of Rs , respectively. The radioactively labeled PCR product was used as probe to hybridize with EcoRI.. BamHI.. HindIII.. Sail Sac I.. A抙ol.. XbaI -digested genomic DNA of 1375 1.They all gave one hybridizing band of about 5.1kb.. 22kb.. 4.4kb.. 22kb.. 11kb.. 23kb and 23kb,respectively. The 5.1 kb EcoRI fragment was cloned and sequenced. One 1938 bp ORF was found to be 95%.. 84% homology with hrcV of Xcv and Rs.This ORF might encode a polypeptide with 645 amino acids, which had 97%.. 75% similarity with Xcv HrcV protein and Rs HrcV protein,respectively. This 5.1 kb EcoRI fragment was saturatedly mutated with Tn5 and nine independent mutant plasmids were isolated.One Tn5 which inserted Ca. 0.8 kb downstream the start codon of the 1938 bp ORF was markerxchanged to the corresponding position of chromosome of 13751 .The mutant could not cause any ? symptoms on rice and elicit HR on nonhost plant Datura strumonium .The Xoo hrcV Tn5 mutant has ability to colonize hydathode of rice leaves and grows normally in rice. A hrcV deletion mutant of 13751 was constructed .The mutant was tested for its ability to protect rice from bacterial blight in the green house .It turned out that the mutant could give 55% efficiency for rice from bacterial blight in the green house.