Search

The present study aimed to evaluate transcriptional activator-like effector (TALE) genes in 86 Xanthomonas oryzae pv. oryzicola strains collected from 8 rice-growing regions in Yunnan, and to examine the relationship between TALE genotypes and virulence in 6 differential rice lines. Besides, the geographical areas, distribution of these genotypes were studied in detail. Genetic diversity was analyzed through the number and size of putative TALE genes based on TALE gene avrXa3 as a probe. We found that X. oryzae pv. oryzicola strains consist of variable number (13–27) of avrXa3-hybridizing fragments (putative TALE genes). Test strains were classified into 8 genotypes (G1–G8) with major genotypes G3 and G7 widely distributed in Yunnan. Pathogenicity of X. oryzae pv. oryzicola was evaluated by inoculating 6 differential rice lines with a single resistance gene into 9 pathotypes clusters (I–IX), the dominant Genotypes G3 and G7 consist of pathotypes I, II, and IV. Furthermore, we also detected the known TALE target genes expression in susceptible rice cultivar (cv. nipponbare) after inoculating 8 genotypes-representative X. oryzae pv. oryzicola strain. Correlation between the numbers of putative TALE genes of X. oryzae pv. oryzicola and relevant target genes in nipponbare confirmed up-regulation. Altogether, this study has given insights into the population structure of X. oryzae pv. oryzicola that may inform strategies to control BLS in rice. [ABSTRACT FROM AUTHOR]

Fermentation products of Lysobacter antibioticus 13-6 have antagonistic activity against devastating phytopathogenic bacerium Xanthomonas oryzae pv. oryzicola. The production of Lysobacter antibioticus 13-6 secondary metabolites was increased by optimizing the fermentation medium; using a single-factor screening test, Plackett–Burman Design, and Box-Behnken Design. The medium's final formulation for active secondary metabolites high-yield included peptone 5 g/L, glucose 4.73 g/L, MgSO4·7H2O 2.33 g/L, and K2HPO4 2.21 g/L. We compared phenazine-1-carboxylic acid (PCA) contents of L. antibioticus 13-6 in the initial and optimized mediums through HPLC. It was found PCA contents of the optimized medium are two folds more than in the initial medium. We also detected the relative expression of five phenazine genes of L. antibioticus 13-6 via RT-qPCR, and it was found that genes: phzB, C, S, and NO1 have more significant expression compared with the initial medium, while gene phzD has found just significant. Further, we revealed that the optimal fermentation conditions for secondary metabolites were: fermentation time 60 hours, shaking speed 160 rpm, inoculum size 3%, and the initial pH = 7.0. In the end, it was determined that the antimicrobial activity and quality of L. antibioticus 13-6 secondary metabolites were increased by about 41.75% and 2-times, respectively, after the optimization of the fermentation medium. [ABSTRACT FROM AUTHOR]

Bacterial leaf streak (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc), impacts the production of rice. However, several rice cultivars displayed resistance to Xoc in the field, but scarce information is available about the role of endophytic microbiota in disease resistance. In the present study, the endophytic bacterial communities of resistant and susceptible rice cultivars "CG2" and "IR24", respectively, were analyzed using high throughput 16S rRNA gene amplified sequencing and culture dependent method was further used for bacterial isolation. A total of 452,716 high-quality sequences representing 132 distinct OTUs (Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes) and 46 isolates of 16 genera were explored from rice leaves infected with Xoc. Community diversity of endophytic bacteria were higher in the leaves of the resistant cultivars compared to susceptible cultivars upon Xoc infection. Strikingly, this diversity might contribute to natural defense of the resistant cultivar against pathogen. Pantoea, which is pathogen antagonist, was frequently detected in two cultivars and higher abundance were recorded in resistant cultivars. Different abundance genus includes endophytic isolates with marked antagonistic activity to Xoc. The increased proportions of antagonistic bacteria, may contribute to resistance of rice cultivar against Xoc and the Pantoea genus was recruited by Xoc infection play a key role in suppressing the development of BLS disease in rice. Taken together, this work reveals the association between endophytic bacteria and BLS resistance in rice and identification of antagonism-Xoc bacterial communities in rice. [ABSTRACT FROM AUTHOR]

Bacterial leaf streak disease caused by Xanthomonas oryzae pv. Oryzicola (Xoc) is a serious threat to rice production worldwide. Like most bacterial phytopathogens, Xoc also contains multiple regulators involved in the complex regulatory networks to ensure its virulence. In this study, we found two genes, FE36_09860 and FE36_06255, through quantitative fluorescence PCR essential for Xoc virulence and might be regulated by the diffusible signal factor (DSF) and the global regulator (Clp). We evaluated the characteristics of the TetR family (FE36_09860) and Fur family (FE36_06255) transcriptional regulator genes in in-vitro and in-vivo experiments. Results demonstrated that the deletion of two transcriptional regulators genes, FE36_09860 and FE36_06255, reduced the virulence of Xoc. Further analysis revealed that the deletion of the FE36_06255 gene results in decreased EPS production, elevated biofilm formation and reactive oxygen species production, and maintained the growth rate of Xoc YM15. In contrast, the deletion of FE36_09860 showed an opposite trend. It is concluded that, as transcriptional regulators, the FE36_09860 and FE36_06255 genes played an important role in the biological processes of Xoc YM15 and were essential for its virulence. • Xoc contains multiple regulators to ensure its virulence. • Genes FE36_09860 and FE36_06255 are important for the virulence of Xoc. • Deletion of FE36_09860 and FE36_06255 reduced the virulence of Xoc. • FE36_09860 and FE36_06255 played an important role in the biological processes. [ABSTRACT FROM AUTHOR]

Bacterial leaf streak caused by Xanthomonas oryzae pv. oryzicola (Xoc) is a devastating disease of rice worldwide, including China. The second messenger c -di-GMP plays an important role in the transduction of intercellular signals. However, little is known about the function of EAL domain protein in c -di-GMP that regulates the virulence in Xoc. In this study, the function of EAL domain protein encoded by pde (FE36_09715) gene in the regulation of c -di-GMP was investigated. Results of this study, showed that the deletion of pde gene led to a significant reduction in the virulence of Xoc and was positively related to the reduction of exopolysaccharides production, biofilm formation, and flagellar motility. However, these significantly impaired properties from the ∆ pde mutant strain were partially recovered in the complementary strain. In addition, the deletion of pde gene in Xoc strain YM15 had no visible effect on the colony morphology, amylase, and protease activities of Xoc. It is concluded that, as a regulator for the c -di-GMP level, the pde gene plays an important role in partial biological processes in Xoc and is essential for its virulence. • Bacterial leaf streak caused by Xanthomonas oryzae pv. oryzicola is a devastating disease of rice. • pde gene plays an important role in the virulence of Xanthomonas oryzae pv. oryzicola. • pde gene is positively related to reductions of exopolysaccharides production, biofilm formation, and flagellar motility. • Deletion of pde gene had no visible effect on colony morphology, amylase, and protease activities. [ABSTRACT FROM AUTHOR]

Bacterial leaf streak of rice (BLS), caused by Xanthomonas oryzae pv. oryzicola (Xoc), is an increasingly serious disease in southwestern China. This study aimed to evaluate the response of the native rice variety Hongyou-4 (HY4) to two different transcription activator-like effectors (TALEs) genotypes of Xoc. HY4 was significantly susceptible to Xoc strain 13T19 and resistant to Xoc strain YM15. Transcriptomic analysis of HY4 leaves inoculated with the two Xoc TALEs genotypes revealed 1339 and 1219 differentially expressed genes (DEGs) in rice inoculated with Xoc strain 13T19 (HY.Q) and Xoc strain YM15 (HY.R), respectively, compared to the control. Quantitative real-time PCR (qRT-PCR) for expression of 10 randomly selected genes was used to verify the RNA-Seq data. Gene ontology (GO) analysis of the transcriptomic data showed DEGs of defense-related genes were predominantly assigned to 11 GO terms, with nine terms showing differential expression in HY4 after inoculation with the two Xoc genotypes. KEGG pathway clustering analysis revealed DEGs involved in plant-pathogen interactions and secondary metabolite pathways of phenylpropanoid biosynthesis were down-regulated in HY.Q compared to HY.R. Four transcription factors including bZIP, GLK, MADS, and MYB families, three resistance genes, and the TalAM2 effector target gene OsSWEET13, were differentially expressed in HY4 inoculated with the two Xoc TALEs genotypes. These data clarify the mechanism of interactions between rice and different TALE genotypes of Xoc , and can help reveal disease-related metabolic pathways, molecular regulatory networks, and candidate genes involved in rice responses to TALEs of Xoc. • Transcriptome profiles of a rice HY4 responding to two Xoc strains 13T19 and YM15 was described. • A local rice variety Hongyou-4, which is of good yield and quality was used. • TAL gene numbers in these two strains are different, implying TAL genes virulence in rice. • We identified 4 transcription factors (TFs), 3 resistance gene and the TalAM2 effector target gene OsSWEET13. • The mechanism of interactions between rice and different TALEs genotypes Xoc was revealed. [ABSTRACT FROM AUTHOR]