The rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo) injects transcription activator-like effectors (TALEs) that bind and activate host 'susceptibility' (S) genes important for disease. Clade III SWEET genes are major S genes for bacterial blight. The resistance genes xa5, which reduces TALE activity generally, and xa13, a SWEET11 allele not recognized by the cognate TALE, have been effectively deployed. However, strains that defeat both resistance genes individually were recently reported in India and Thailand. To gain insight into the mechanism(s), we completely sequenced the genome of one such strain from each country and examined the encoded TALEs. Strikingly, the two strains are clones, sharing nearly identical TALE repertoires, including a TALE known to activate SWEET11 strongly enough to be effective even when diminished by xa5. We next investigated SWEET gene induction by the Indian strain.The Indian strain induced no clade III SWEET in plants harbouring xa13, indicating a pathogen adaptation that relieves dependence on these genes for susceptibility. The findings open a door to mechanistic understanding of the role SWEET genes play in susceptibility and illustrate the importance of complete genome sequence-based monitoring of Xoo populations in developing varieties with effective disease resistance.
Co-utilization of xylose and glucose and subsequent fermentation using Saccharomyces
cerevisiae could enhance ethanol productivity. Directed engineering approaches have met
with limited success due to interconnectivity of xylose metabolism with other intrinsic,
hidden pathways. Therefore, random approaches like protoplast fusion were used to
reprogram unidentified mechanisms.
Saccharomyces cerevisiae LN, the best hexose fermenter, was fused with xylose
fermenting Pichia stipitis NCIM 3498. Protoplasts prepared using glucanex were fused under
electric impulse and fusants were selected using 10% ethanol and cycloheximide (50 ppm)
markers. Two fusants, 1a.23 and 1a.30 showing fast growth on xylose and tolerance to 10%
ethanol, were selected. Higher extracellular protein expression observed in fusants as
compared to parents was corroborated by higher number of bands resolved by twodimensional analysis.
Overexpression of XYL1, XYL2, XKS and XUT4 in fusants as compared to S.
cerevisiae LN as observed by RT-PCR analysis was substantiated by higher specific activities
of XR, XDH and XKS enzymes in fusants. During lignocellulosic hydrolysate fermentation,
fusants could utilize glucose faster than the parent P. stipitis NCIM 3498 and xylose
consumption in fusants was higher than S. cerevisiae LN.
The rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo) injects transcription activator-like effectors (TALEs) that bind and activate host “susceptibility” (S) genes important for disease. Clade III SWEET genes are major S genes for bacterial blight. The resistance genes xa5, which reduces TALE activity generally, and xa13, a SWEET11 allele not recognized by the cognate TALE, have been effectively deployed. However, strains that defeat both resistance genes individually were recently reported in India and Thailand. To gain insight into the mechanism(s), we completely sequenced the genome of one such strain from each country and examined the encoded TALEs. Strikingly, the two strains are clones, sharing nearly identical TALE repertoires, including a TALE known to activate SWEET11 strongly enough to be effective even when diminished by xa5. We next investigated SWEET gene induction by the Indian strain. The Indian strain induced no clade III SWEET in plants harboring xa13, indicating a pathogen adaptation that relieves dependence on these genes for susceptibility. The findings open a door to mechanistic understanding of the role SWEET genes play in susceptibility and illustrate the importance of complete genome sequence-based monitoring of Xoo populations in developing varieties with effective disease resistance.
Co-utilization of xylose and glucose and subsequent fermentation using Saccharomyces cerevisiae could enhance ethanol productivity. Directed engineering approaches have met with limited success due to interconnectivity of xylose metabolism with other intrinsic, hidden pathways. Therefore, random approaches like protoplast fusion were used to reprogram unidentified mechanisms.Saccharomyces cerevisiae LN, the best hexose fermenter, was fused with xylose fermenting Pichia stipitis NCIM 3498. Protoplasts prepared using glucanex were fused under electric impulse and fusants were selected using 10% ethanol and cycloheximide (50 ppm) markers. Two fusants, 1a.23 and 1a.30 showing fast growth on xylose and tolerance to 10% ethanol, were selected. Higher extracellular protein expression observed in fusants as compared to parents was corroborated by higher number of bands resolved by twodimensional analysis.Overexpression of XYL1, XYL2, XKS and XUT4 in fusants as compared to S. cerevisiae LN as observed by RT-PCR analysis was substantiated by higher specific activities of XR, XDH and XKS enzymes in fusants. During lignocellulosic hydrolysate fermentation, fusants could utilize glucose faster than the parent P. stipitis NCIM 3498 and xylose consumption in fusants was higher than S. cerevisiae LN.
The rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo) constrains production in major rice growing countries of Asia. Xoo injects transcription activator-like effectors (TALEs) that bind to and activate host "susceptibility" (S) genes that are important for disease. The bacterial blight resistance gene xa5, which reduces TALE activity generally, has been widely deployed. However, strains defeating xa5 have been reported in India and recently also in Thailand. We completely sequenced and compared the genomes of one such strain from each country and examined the encoded TALEs. The two genomes are nearly identical, including the TALE genes, and belong to a previously identified, highly clonal lineage. Each strain harbors a TALE known to activate the major S gene SWEET11 strongly enough to be effective even when diminished by xa5. The findings suggest international migration of the xa5-compatible pathotype and highlight the utility of whole genome sequencing and TALE analysis for understanding and responding to breakdown of resistance.
Cauliflower is an important extensively grown cool season vegetable in India. Black rot and downy mildew are major devastating diseases reducing yield and quality of the crop. To tackle these through host plant resistance, a marker-assisted backcross breeding method was followed to pyramid a black rot-resistant gene (Xca1bo) and a downy mildew-resistant gene (Ppa3) from donors BR-161 and BR-2, respectively, into the background of Pusa Meghna cauliflower cultivar. Marker-assisted backcross breeding was followed up to BC2 generation using SCAR marker ScOPO-04833 and SSR marker BoGMS0624 for black rot and downy mildew resistance genes in foreground selection, respectively. In background selection, at each stage of backcrossing, 47 parental polymorphic SSR markers were used. The graphical genotyping of the five two-gene (Xca1boXca1boPpa3Ppa3) homozygous BC2F2 plants showed an average recovery of 85.44% of the Pusa Meghna genome with highest genome recovery of 91.7%. The genome contribution of donor parents (BR-161 and BR-2) was 8.26 with 6.34% of residual heterozygousity. The backcross derived pyramided lines BC2F2:3-7-16 and BC2F2:3-7-33 showed high resistance to both the diseases and exhibited higher yield and vitamin C content as compared with recipient parent Pusa Meghna. It is, therefore, evident from this study that resistant genes can be introgressed successfully into a Pusa Meghna cultivar without any yield penalty, benefitting farmers with reduced input cost and consumers with chemical residue free produce. Besides, the pyramided lines carrying dominant resistant genes can be exploited in a hybridization programme to develop hybrid(s) in cauliflower.
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