Complete genome sequence and pathogenic genes analysis of Pectobacterium atroseptica JG10-08

The C3H gene PtZFP2-like in Pinellia ternata acts as a positive regulator of the resistance to soft rot caused by Pectobacterium carotovorum

Pinellia ternata (Thunb.) Breit is a member of the Araceae family and is globally distributed. The dry tuber has been used as a traditional Chinese medicine for over 2,000 years. With agricultural development, the harm of soft rot to P. ternata is an increasing problem. The lack of germplasm resources resistant to soft rot leads to less research on resistance mechanisms. In our study, we screened disease-resistant P. ternata P-1 and disease-susceptible P. ternata P-4 for the first time. Then, the infection of soft rot for 0, 24, and 48 hours was performed, and a de novo transcriptome analysis explored key genes associated with soft rot resistance. A total of 260,169 unigenes were identified and differentially expressed gene analysis was conducted. In total, 33 C3H-type ZFP genes were differentially expressed under Pectobacterium carotovorum infection. Transient expression of ZFP2-like (Cluster-5189.85444) resulted in a twofold increase at 24 hour post infection (hpi) and a threefold increase at 48 hpi in P-1 with soft rot infection, but no significant difference at P-4 enhanced the resistance of Nicotiana benthamiana to soft rot. Stable overexpression in P. ternata with a 2 ~ 11-fold increase in gene expression and reduced the lesion size from 6 mm to 2 ~ 4 mm at 24 hpi, demonstrating increased resistance to P. carotovorum. These findings indicated the ZFP2-like gene plays a pivotal role in soft rot resistance, enriches genetic data on disease resistance in P. ternata, and contributes to breed selection and improvement.

Repurposing Salicylamides to Combat Phytopathogenic Bacteria and Induce Plant Defense Responses

Based on the research strategy of "drug repurposing", a series of derivatives and marketed drugs that containing salicylic acid skeleton were tested for their antibacterial activities against phytopathogens. Salicylic acid can not only regulate some important growth metabolism of plants, but also induce plant disease resistance. The bioassay results showed that the salicylamides exhibited excellent antibacterial activity. Especially, oxyclozanide showed the best antibacterial effect against Xanthomonas oryzae, Xanthomonas axonopodis pv. citri and Pectobacterium atroseptica with MICs of 0.78, 3.12 and 12.5 μg.mL-1, respectively. In vivo experiments with rice bacterial leaf blight had further demonstrated that oxyclozanide exhibited stronger antibacterial activity than the commercial bactericide, thiodiazole copper. Oxyclozanide could induce plant defense responses through the determination of salicylic acid content and the activities of defense-related enzymes including CAT, POD, and SOD in rice. The preliminarily antibacterial mechanism study indicated that oxyclozanide exhibited the antibacterial activity by disrupting cell integrity and reducing bacterial pathogenicity. Additionally, oxyclozanide could induce plant defense responses through the determination of salicylic acid content.

Analysis of the Taxonomy and Pathogenic Factors of Pectobacterium aroidearum L6 Using Whole-Genome Sequencing and Comparative Genomics

Soft rot pectobacteria are devastating plant pathogens with a global distribution and a broad host range. Pectobacterium aroidearum L6, previously isolated from leaves of Syngonium podophyllum, is a pectolytic bacterial pathogen that causes typical soft rot on S. podophyllum. There is a shortage for genome data of P. aroidearum, which seriously hinders research on classification and pathogenesis of Pectobacterium. We present here the complete genome sequence of P. aroidearum L6. The L6 strain carries a single 4,995,896-bp chromosome with 53.10% G + C content and harbors 4,306 predicted protein-coding genes. We estimated in silico DNA-DNA hybridization and average nucleotide identity values in combination with the whole-genome-based phylogeny from 19 Pectobacterium strains including P. aroidearum L6. The results showed that L6 and PC1 formed a population distinct from other populations of the Pectobacterium genus. Phylogenetic analysis based on 16S rRNA and genome sequences showed a close evolutionary relationship among Pectobacterium species. Overall, evolutionary analysis showed that L6 was in the same branch with PC1. In comparison with 18 Pectobacterium spp. reference pathogens, strain L6 had 2,712 gene families, among which 1,632 gene families were identified as orthologous to those strains, as well as 1 putative unique gene family. We discovered 478 genes, 10.4% of the total of predicted genes, that were potentially related to pathogenesis using the Virulence Factors of Pathogenic Bacteria database. A total of 25 genes were related to toxins, 35 encoded plant cell-wall degrading enzymes, and 122 were involved in secretion systems. This study provides a foundation for a better understanding of the genomic structure of P. aroidearum and particularly offers information for the discovery of potential pathogenic factors and the development of more effective strategies against this pathogen.