Complete genome sequence analysis of the peanut pathogen Ralstonia solanacearum strain Rs-P.362200

A Ralstonia effector RipAU impairs peanut AhSBT1.7 immunity for pathogenicity via AhPME-mediated cell wall degradation

Bacterial wilt caused by Ralstonia solanacearum is a devastating disease affecting a great many crops including peanut. The pathogen damages plants via secreting type Ш effector proteins (T3Es) into hosts for pathogenicity. Here, we characterized RipAU was among the most toxic effectors as ΔRipAU completely lost its pathogenicity to peanuts. A serine residue of RipAU is the critical site for cell death. The RipAU targeted a subtilisin-like protease (AhSBT1.7) in peanut and both protein moved into nucleus. Heterotic expression of AhSBT1.7 in transgenic tobacco and Arabidopsis thaliana significantly improved the resistance to R. solanacearum. The enhanced resistance was linked with the upregulating ERF1 defense marker genes and decreasing pectin methylesterase (PME) activity like PME2&4 in cell wall pathways. The RipAU played toxic effect by repressing R-gene, defense hormone signaling, and AhSBTs metabolic pathways but increasing PMEs expressions. Furthermore, we discovered AhSBT1.7 interacted with AhPME4 and was colocalized at nucleus. The AhPME speeded plants susceptibility to pathogen via mediated cell wall degradation, which inhibited by AhSBT1.7 but upregulated by RipAU. Collectively, RipAU impaired AhSBT1.7 defense for pathogenicity by using PME-mediated cell wall degradation. This study reveals the mechanism of RipAU pathogenicity and AhSBT1.7 resistance, highlighting peanut immunity to bacterial wilt for future improvement.

A novel type III effector RipBU from Ralstonia solanacearum suppresses plant immunity and promotes peanut susceptibility

A predicted peanut R. solanacearum T3E RS_T3E_Hyp6 was identified as a definite T3E and renamed as RipBU. It is relative conserved in 31 R. solanacearum strains. Deletion of RipBU in R. solanacearum HA4-1 strain caused the attenuate pathogenicity in peanut, and complementarity of RipBU recovered the virulence of ΔRipBU mutant strain. Transient expression of RipBU decreased the level of chlorophyll, resulting in leaf chlorosis and suppressed flg22-triggered reactive oxygen species (ROS) burst and the expression of pattern-triggered immunity (PTI) marker genes in the leaves of Nicotiania benthamiana. Subcellular localization observation showed that RipBU localizes to chloroplasts in tobacco cells. RipBU significantly increased the jasmonic acid (JA) content and the expressions of JA-signaling marker genes in tobacco leaves, while significantly decreased the salicylic acid (SA) level and the expressions of SA-signaling marker genes. RipBU contained a putative lipase domain, and mutation of which abolished the ability of RipBU to induce tobacco leaf chlorosis and peanut wilt, while still localized to chloroplasts. Our study reveals the virulence function of RipBU that suppresses plant immunity by inhibiting PTI and SA signaling, and promoting JA signaling.

Whole-Genome Sequence and Characterization of Ralstonia solanacearum MLY102 Isolated from Infected Tobacco Stalks

BACKGROUND/OBJECTIVES

Bacterial wilt disease is a soil-borne disease caused by Ralstonia solanacearum that causes huge losses to crop economies worldwide.

METHODS

In this work, strain MLY102 was isolated and further identified as R. solanacearum from a diseased tobacco stalk. The genomic properties of MLY102 were explored by performing biochemical characterization, genome sequencing, compositional analysis, functional annotation and comparative genomic analysis.

RESULTS

MLY102 had a pinkish-red color in the center of the colony surrounded by a milky-white liquid with fluidity on TTC medium. The biochemical results revealed that MLY102 can utilize carbon sources, including D-glucose (dGLU), cane sugar (SAC) and D-trehalose dihydrate (dTRE). Genome sequencing through the DNBSEQ and PacBio platforms revealed a genome size of 5.72 Mb with a G+C content of 67.59%. The genome consists of a circular chromosome and a circular giant plasmid with 5283 protein-coding genes. A comparison of the genomes revealed that MLY102 is closely related to GMI1000 and CMR15 but has 498 special genes and 13 homologous genes in the species-specific gene family, indicating a high degree of genomic uniqueness.

CONCLUSIONS

The unique characteristics and genomic data of MLY102 can provide important reference values for the prevention and control of bacterial wilt disease.

Pathogenic and Comparative Genomic Analysis of Ralstonia pseudosolanacearum Isolated from Casuarina

Casuarina equisetifolia is crucial in protecting coastal regions of China against typhoon attacks but has faced a substantial challenge due to wilt disease caused by pathogens of the Ralstonia solanacearum species complex (RSSC). Although the initial outbreak of Casuarina wilt in the 1970s was effectively controlled by disease-resistant C. equisetifolia varieties, the disease has recently re-emerged in coastal regions of Guangdong. In this study, we report the isolation, characterization, and comparative genomic analysis of 11 RSSC strains from diseased C. equisetifolia at various locations along the coast of Guangdong. Phylogenomic analysis showed that the strains were closely related and clustered with phylotype I strains previously isolated from peanuts. Single-gene-based analysis further suggested these strains could be derived from strains present in Guangdong since the 1980s, indicating a historical context to their current pathogenicity. Casuarina-isolated strains exhibited notably higher virulence against C. equisetifolia and peanuts than the representative RSSC strains GMI1000 and EP1, suggesting host-specific adaptations that possibly contributed to the recent outbreak. Comparative genomic analysis among RSSC strains revealed a largely conserved genome structure and high levels of conservation in gene clusters encoding extracellular polysaccharide biosynthesis, secretion systems, and quorum sensing regulatory systems. However, we also found a number of unique genes in the Casuarina-isolated strains that were absent in GMI1000 and EP1, and vice versa, pointing to potential genetic factors underpinning their differential virulence. These unique genes offer promising targets for future functional studies. Overall, our findings provide crucial insights into the RSSC pathogens causing Casuarina wilt in Guangdong, guiding future efforts in disease control and prevention.

Comparative genomics and host range analysis of four Ralstonia pseudosolanacearum strains isolated from sunflower reveals genomic and phenotypic differences

BACKGROUND

Bacterial wilt caused by Ralstonia solanacearum species complex (RSSC) is one of the devastating diseases in crop production, seriously reducing the yield of crops. R. pseudosolanacearum, is known for its broad infrasubspecific diversity and comprises 36 sequevars that are currently known. Previous studies found that R. pseudosolanacearum contained four sequevars (13, 14, 17 and 54) isolated from sunflowers sown in the same field.

RESULTS

Here, we provided the complete genomes and the results of genome comparison of the four sequevars strains (RS639, RS642, RS647, and RS650). Four strains showed different pathogenicities to the same cultivars and different host ranges. Their genome sizes were about 5.84 ~ 5.94 Mb, encoding 5002 ~ 5079 genes and the average G + C content of 66.85% ~ 67%. Among the coding genes, 146 ~ 159 specific gene families (contained 150 ~ 160 genes) were found in the chromosomes and 34 ~ 77 specific gene families (contained 34 ~ 78 genes) in the megaplasmids from four strains. The average nucleotide identify (ANI) values between any two strains ranged from 99.05% ~ 99.71%, and the proportion of the total base length of collinear blocks accounts for the total gene length of corresponding genome was all more than 93.82%. Then, we performed a search for genomic islands, prophage sequences, the gene clusters macromolecular secretion systems, type III secreted effectors and other virulence factors in these strains, which provided detailed comparison results of their presence and distinctive features compared to the reference strain GMI1000. Among them, the number and types of T2SS gene clusters were different in the four strains, among which RS650 included all five types. T4SS gene cluster of RS639 and RS647 were missed. In the T6SS gene cluster, several genes were inserted in the RS639, RS647, and RS650, and gene deletion was also detected in the RS642. A total of 78 kinds of type III secreted effectors were found, which included 52 core and 9 specific effectors in four strains.

CONCLUSION

This study not only provided the complete genomes of multiple R. pseudosolanacearum strains isolated from a new host, but also revealed the differences in their genomic levels through comparative genomics. Furthermore, these findings expand human knowledge about the range of hosts that Ralstonia can infect, and potentially contribute to exploring rules and factors of the genetic evolution and analyzing its pathogenic mechanism.

Complete genome sequence of the Pogostemon cablin bacterial wilt pathogen Ralstonia solanacearum strain SY1

BACKGROUND

Ralstonia solanacearum causes bacterial wilt of Pogostemon cablin which is an important aromatic herb and also the main materials of COVID-19 therapeutic traditional drugs. However, we are lacking the information on the genomic sequences of R. solanacearum isolated from P. cablin.

OBJECTIVE

The acquisition and analysis of this whole-genome sequence of the P. cablin bacterial wilt pathogen.

METHODS

An R. solanacearum strain, named SY1, was isolated from infected P. cablin plants, and the complete genome sequence was sequenced and analyzed.

RESULTS

The SY1 strain contains a 3.70-Mb chromosome and a 2.18-Mb megaplasmid, with GC contents of 67.57% and 67.41%, respectively. A total of 3308 predicted genes were located on the chromosome and 1657 genes were located in the megaplasmid. SY1 strain has 273 unique genes compared with five representative R. solanacearum strains, and these genes were enriched in the plant-pathogen interaction pathway. SY1 possessed a higher syntenic relationship with phylotype I strains, and the arsenal of type III effectors predicted in SY1 were also more closely related to those of phylotype I strains. SY1 contained 14 and 5 genomic islands in its chromosome and megaplasmid, respectively, and two prophage sequences in its chromosome. In addition, 215 and 130 genes were annotated as carbohydrate-active enzymes and antibiotic resistance genes, respectively.

CONCLUSION

This is the first genome-scale assembly and annotation for R. solanacearum which isolated from infected P. cablin plants. The arsenal of virulence and antibiotic resistance may as the determinants in SY1 for infection of P. cablin plants.

Comprehensive genome sequence analysis of the devastating tobacco bacterial phytopathogen Ralstonia solanacearum strain FJ1003

Due to its high genetic diversity and broad host range, Ralstonia solanacearum, the causative phytopathogen of the bacterial wilt (BW) disease, is considered a "species complex". The R. solanacearum strain FJ1003 belonged to phylotype I, and was isolated from the Fuzhou City in Fujian Province of China. The pathogen show host specificity and infects tobacco, especially in the tropical and subtropical regions. To elucidate the pathogenic mechanisms of FJ1003 infecting tobacco, a complete genome sequencing of FJ1003 using single-molecule real-time (SMRT) sequencing technology was performed. The full genome size of FJ1003 was 5.90 Mb (GC%, 67%), containing the chromosome (3.7 Mb), megaplasmid (2.0 Mb), and small plasmid (0.2 Mb). A total of 5133 coding genes (3446 and 1687 genes for chromosome and megaplasmid, respectively) were predicted. A comparative genomic analysis with other strains having the same and different hosts showed that the FJ1003 strain had 90 specific genes, possibly related to the host range of R. solanacearum. Horizontal gene transfer (HGT) was widespread in the genome. A type Ⅲ effector protein (Rs_T3E_Hyp14) was present on both the prophage and genetic island (GI), suggesting that this gene might have been acquired from other bacteria via HGT. The Rs_T3E_Hyp14 was proved to be a virulence factor in the pathogenic process of R. solanacearum through gene knockout strategy, which affects the pathogenicity and colonization ability of R. solanacearum in the host. Therefore, this study will improve our understanding of the virulence of R. solanacearum and provide a theoretical basis for tobacco disease resistance breeding.

Complete Genome Sequence Analysis of Ralstonia solanacearum Strain PeaFJ1 Provides Insights Into Its Strong Virulence in Peanut Plants

The bacterial wilt of peanut (Arachis hypogaea L.) caused by Ralstonia solanacearum is a devastating soil-borne disease that seriously restricted the world peanut production. However, the molecular mechanism of R. solanacearum–peanut interaction remains largely unknown. We found that R. solanacearum HA4-1 and PeaFJ1 isolated from peanut plants showed different pathogenicity by inoculating more than 110 cultivated peanuts. Phylogenetic tree analysis demonstrated that HA4-1 and PeaFJ1 both belonged to phylotype I and sequevar 14M, which indicates a high degree of genomic homology between them. Genomic sequencing and comparative genomic analysis of PeaFJ1 revealed 153 strain-specific genes compared with HA4-1. The PeaFJ1 strain-specific genes consisted of diverse virulence-related genes including LysR-type transcriptional regulators, two-component system-related genes, and genes contributing to motility and adhesion. In addition, the repertoire of the type III effectors of PeaFJ1 was bioinformatically compared with that of HA4-1 to find the candidate effectors responsible for their different virulences. There are 79 effectors in the PeaFJ1 genome, only 4 of which are different effectors compared with HA4-1, including RipS4, RipBB, RipBS, and RS_T3E_Hyp6. Based on the virulence profiles of the two strains against peanuts, we speculated that RipS4 and RipBB are candidate virulence effectors in PeaFJ1 while RipBS and RS_T3E_Hyp6 are avirulence effectors in HA4-1. In general, our research greatly reduced the scope of virulence-related genes and made it easier to find out the candidates that caused the difference in pathogenicity between the two strains. These results will help to reveal the molecular mechanism of peanut–R. solanacearum interaction and develop targeted control strategies in the future.