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The Xa7 resistance gene guards the rice susceptibility gene SWEET14 against exploitation by the bacterial blight pathogen.

ABSTRACT: Many plant disease resistance (R) genes function specifically in reaction to the presence of cognate effectors from a pathogen. Xanthomonas oryzae pathovar oryzae (Xoo) uses transcription activator-like effectors (TALes) to target specific rice genes for expression, thereby promoting host susceptibility to bacterial blight. Here, we report the molecular characterization of Xa7, the cognate R gene to the TALes AvrXa7 and PthXo3, which target the rice major susceptibility gene SWEET14. Xa7 was mapped to a unique 74-kb region. Gene expression analysis of the region revealed a candidate gene that contained a putative AvrXa7 effector binding element (EBE) in its promoter and encoded a 113-amino-acid peptide of unknown function. Genome editing at the Xa7 locus rendered the plants susceptible to avrXa7-carrying Xoo strains. Both AvrXa7 and PthXo3 activated a GUS reporter gene fused with the EBE-containing Xa7 promoter in Nicotiana benthamiana. The EBE of Xa7 is a close mimic of the EBE of SWEET14 for TALe-induced disease susceptibility. Ectopic expression of Xa7 triggers cell death in N. benthamiana. Xa7 is prevalent in indica rice accessions from 3000 rice genomes. Xa7 appears to be an adaptation that protects against pathogen exploitation of SWEET14 and disease susceptibility.

SUBMITTER: Luo D

PROVIDER: S-EPMC8132128 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Plant disease is a major challenge to agriculture worldwide, and it is exacerbated by abiotic environmental factors. During some plant-pathogen interactions, heat stress allows pathogens to overcome host resistance, a phenomenon which could severely impact crop productivity considering the global warming trends associated with climate change. Despite the importance of this phenomenon, little is known about the underlying molecular mechanisms. To better understand host plant responses during simultaneous heat and pathogen stress, we conducted a transcriptomics experiment for rice plants (cultivar IRBB61) containing Xa7, a bacterial blight disease resistance (R) gene, that were infected with Xanthomonas oryzae, the bacterial blight pathogen of rice, during high temperature stress. Xa7-mediated resistance is unusual relative to resistance mediated by other R genes in that it functions better at high temperatures. Using RNA-Seq technology, we identified 8,499 differentially expressed genes as temperature responsive in rice cultivar IRBB61 experiencing susceptible and resistant interactions across three time points. Notably, genes in the plant hormone abscisic acid biosynthesis and response pathways were up-regulated by high temperature in both mock-treated plants and plants experiencing a susceptible interaction and were suppressed by high temperature in plants exhibiting Xa7-mediated resistance. Genes responsive to salicylic acid, an important plant hormone for disease resistance, were down-regulated by high temperature during both the susceptible and resistant interactions, suggesting that enhanced Xa7-mediated resistance at high temperature is not dependent on salicylic acid signaling. A DNA sequence motif similar to known abscisic acid-responsive cis-regulatory elements was identified in the promoter region upstream of genes up-regulated in susceptible but down-regulated in resistant interactions. The results of our study suggest that the plant hormone abscisic acid is an important node for cross-talk between plant transcriptional response pathways to high temperature stress and pathogen attack. Genes in this pathway represent an important focus for future study to determine how plants evolved to deal with simultaneous abiotic and biotic stresses.

Project description:Potential biological control agents for two major rice diseases, sheath blight and bacterial panicle blight, were isolated from rice plants in this study. Rice-associated bacteria (RABs) isolated from rice plants grown in the field were tested for their antagonistic activities against the rice pathogens, Rhizoctonia solani and Burkholderia glumae, which cause sheath blight and bacterial panicle blight, respectively. Twenty-nine RABs were initially screened based on their antagonistic activities against both R. solani and B. glumae. In follow-up retests, 26 RABs of the 29 RABs were confirmed to have antimicrobial activities, but the rest three RABs did not reproduce any observable antagonistic activity against R. solani or B. glumae. According to16S rDNA sequence identity, 12 of the 26 antagonistic RABs were closest to Bacillus amyloliquefaciens, while seven RABs were to B. methylotrophicus and B, subtilis, respectively. The 16S rDNA sequences of the three non-antagonistic RABs were closest to Lysinibacillus sphaericus (RAB1 and RAB12) and Lysinibacillus macroides (RAB5). The five selected RABs showing highest antimicrobial activities (RAB6, RAB9, RAB16, RAB17S, and RAB18) were closest to B. amyloliquefaciens in DNA sequence of 16S rDNA and gyrB, but to B. subtilis in that of recA. These RABs were observed to inhibit the sclerotial germination of R. solani on potato dextrose agar and the lesion development on detached rice leaves by artificial inoculation of R. solani. These antagonistic RABs also significantly suppressed the disease development of sheath blight and bacterial panicle blight in a field condition, suggesting that they can be potential biological control agents for these rice diseases. However, these antagonistic RABs showed diminished disease suppression activities in the repeated field trial conducted in the following year probably due to their reduced antagonistic activities to the pathogens during the long-term storage in -70C, suggesting that development of proper storage methods to maintain antagonistic activity is as crucial as identification of new biological control agents.

Project description:TITLE: Transcriptional profiling of Rgene-mediated responses in rice PROJECT DESCRIPTION: The dominant gene Xa7 and the recessive gene xa5 of rice confer resistance to several races of the bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo). To reveal the modes of action and the defense responses these genes initiate, we decided to obtain the global transcriptional profiles of the rice cultivars IRBB7, IRBB5 (which harbor Xa7 and xa5, respectively) and IR24 undergoing early infection by the Xoo Race 2 strain PXO86. Both IRBB7 and IRBB5 are resistant to PXO86 (which carry the corresponding avirulence genes avrXa7 and avrxa5), whereas IR24 is susceptible. We inoculated by vacuum infiltration the three rice cultivars ten days after seed germination (or 2 weeks after sowing) and collected inoculated tissue at 5 different timepoints within the first day after inoculation. The transcriptional profiles obtained will provide valuable insight into the similarities and differences between incompatible interactions mediated by a dominant and a recessive Rgene, in comparison to a compatible interaction. ****[PLEXdb(http://www.plexdb.org) has submitted this series at GEO on behalf of the original contributor, David O Nino-Liu. The equivalent experiment is OS4 at PLEXdb.] genotype: IR24 - time: 0 hai(3-replications); genotype: IR24 - time: 3 hai(3-replications); genotype: IR24 - time: 6 hai(3-replications); genotype: IR24 - time: 12 hai(3-replications); genotype: IR24 - time: 24 hai(3-replications); genotype: IRBB5 - time: 0 hai(3-replications); genotype: IRBB5 - time: 3 hai(3-replications); genotype: IRBB5 - time: 6 hai(3-replications); genotype: IRBB5 - time: 12 hai(3-replications); genotype: IRBB5 - time: 24 hai(3-replications); genotype: IRBB7 - time: 0 hai(3-replications); genotype: IRBB7 - time: 3 hai(3-replications); genotype: IRBB7 - time: 6 hai(3-replications); genotype: IRBB7 - time: 12 hai(3-replications); genotype: IRBB7 - time: 24 hai(3-replications)

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The Xa7 resistance gene guards the rice susceptibility gene SWEET14 against exploitation by the bacterial blight pathogen.

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