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  1. May 2019
    1. β- galactosidase assay was performed in a 96 well format. Briefly, 4000-5000 cells were plated in 96 well tissue culture coated plate. Cells were transfected with reporter plasmid after 18 -24 hrs and after 48 hrs the cells were washed once with D-PBS. 50μl of lysis buffer was added to the well and cells were lysed by freezing plate at -70°C and thawing at 37°C. Cells were pipette up and down and then the plate was centrifuged at 9000 X g for 5 minutes. The supernatant from each plate was transferred to clean eppendorf tube. Immediately prior to assay the ONPG cocktail was prepared as below: 47 μl 0.1 M sodium phosphate (pH 7.5)22 μl 4 mg/ml ONPG1 μl 100X Mg solution30μl of each well extract was added to microtitre well plate and70μl of ONPG cocktail was added to each well. The plate was kept on ice throughout the procedure. After addition of ONPG cocktail the plate was transferred to 37°C and the development of colour was monitored every 10 minutes for development of color. After development of yellow colour, the reaction was stopped by addition of 150μl of 1M sodium carbonate to each well
    1. A microtipful of cellsfor each yeaststrainfrom appropriate mediumwassuspended in 10μlzymolyase cocktailandincubated at 37ºC for 90 min. 2 μlof zymolyase-treated cell suspension was used as template in 25 μlPCR reaction
    1. (SCR65/ SCR66, SCR63/ SCR64 and SCR61/SCR62, respectively) designed from the neighbourhood region of the deleted gene.Replacement of ΔrpfFdeletion mutant with the point mutant allele (E141A and E161A: Glutamate to Alanine) (rpfF*) was carried out by transforming XocΔrpfFmutant with pbsks suicide vector harbouring full length rpfF* allele. The DNA fragment carrying the rpfF* allele was constructed by overlap PCR as described previously (Ionescu et al., 2013)using two 21 and 28 bp complementary primers for E141A-F/R and E161A-F/R, respectively; harbouring GAA to GCA substitution (Table 2.2). The mutated rpfF* allele was amplified by using the end primers only (SC14 and SC17) and cloned into pbsks vector with HindIII and XhoI restriction sites. The resulting suicide vector (pRR16 and pRR17) was transformed into ΔrpfFmutant and single recombinants were selected on PSA medium with kanamycin and ampicillin. Colonies were screened for integration of rpfF* (E141A or E161A) allele through homologous recombination with the flanking region of deleted rpfF allele
    2. electroporation. Single Kmr recombinants were selected on PSA plate containing kanamycin. Insertion of the pK18mob vector in xssAgene was confirmed with PCR and sequencing. To further confirm the mutation in the siderophore biosynthetic gene, we did siderophore production assay on Peptone-sucrose agar (PSA)-chrome azurol sulfonate (CAS) (Schwyn and Neilands, 1987). PSA-CAS plate assay indicated that the xssA mutnat of Xocwas deficient in production of secreted siderophore.Deletion of the chromosomal rpfG, rpfC andclpgene of the X. oryzaepv. oryzicolawas accomplished by allelic exchange, following homologous recombination, utilizing the suicide vector pK18mobsacB harboring 5’ region and 3’ regions of the gene of interest (Katzen et al., 1999). 5’ and 3’ regions of rpfG and rpfC andclp gene were first amplified from the BXOR1by PCR using primers indicated in Table no. 2.2 and products were ligated together. After restriction digestion of ligated PCR products and the pK18mobsacB vector with appropriate restriction enzymes, they were ligated to get the plasmids pRR9, pRR10 and pRR11, respectively. These plasmids were then transformed into E. coliDH5α cells. The transformed E. colicells were selected on the LB agar plates containing nalidixic acid and kanamycin. The positive colonies carrying vector with correct inserts were further selected by colony PCR. These donor cells carrying pRR9, pRR10 and pRR11 containing 5’ and 3’ regions of the gene of interest were then transformed into electrocompetent BXOR1 wild-typecells. First crossover (single crossover) was achieved by culturing the cell mixture on Nutrient agar(NA) containing rifampicin and kanamycin,after transformation. The second crossover was allowed by passaging the cells with single crossover in nutrient brothmedium and then selecting on PSAplates containing rifampicin and 5% sucrose. BXOR1with deletion of the rpfG,rpfCand clp genes by double crossover was identified by PCR using pri


    3. Two fragments, each approximately 300 bp in length corresponding to 5’and 3’ end of the rpfFgene were amplified using genomic DNA of Xocwild-type strain BXOR1, and cloned in pBSKS vector to obtain pRR7 (Table S1 and S5). pRR8 was obtained after ligation of Kmrcassette (EZ::Tn5TM<Kan-2>; Madison, WI) in the HindIII site of pRR7. The resulting plasmid (pRR8) was introduced into XocBXOR1 strain by electroporation. Doublerecombinants (Kmrand Aps) were screened on PSA plates containing appropriate antibiotics. Deletion of rpfF(76 amino acids) in the ∆rpfF mutant strain was confirmed by PCR and sequencing. For complementation analysis, full lengthrpfF gene was amplifiedfrom genomic DNA of Xoc Wild-typeBXOR1 strain with HindIII and EcoRI restriction sites and cloned into stable broad host range vector pHM1 (Hopkins et al., 1992)downstream to lacZpromoter to obtain pSC9. The pSC9 plasmid harboring the wild-typerpfFallele was introduced into ∆rpfF mutant strain by electroporation.To obtain the insertional nonpolar mutant in the xssA(xanthomonas siderophore synthesis A), a 321 bp internal fragment of the xssAgene containing the XbaI and HindIII sites was cloned inpK18mob suicide vector, in which the lacZpromoter drives the expression of downstream gene (Schäfer et al., 1994; Windgassen et al., 2000)to obtain pRR12. The resulting plasmid (pRR12) was introduced into Xoc BXOR1 strain by