Analysis of the Taxonomy, Synteny, and Virulence Factors for Soft Rot Pathogen Pectobacterium aroidearum in Amorphophallus konjac Using Comparative Genomics

Pangenomics to understand prophage dynamics in the Pectobacterium genus and the radiating lineages of Pectobacterium brasiliense

Bacterial pathogens of the genus Pectobacterium are responsible for soft-rot and blackleg diseases in a wide range of crops and have a global impact on food production. The emergence of new lineages and their competitive succession is frequently observed in Pectobacterium species, in particular in Pectobacterium brasiliense. With a focus on one such recently emerged P. brasiliense lineage in the Netherlands that causes blackleg in potatoes, we studied genome evolution in this genus using a reference-free graph-based pangenome approach. We clustered 1,977,865 proteins from 454 Pectobacterium spp. genomes into 30,156 homology groups. The Pectobacterium genus pangenome is open, and its growth is mainly contributed by the accessory genome. Bacteriophage genes were enriched in the accessory genome and contributed 16% of the pangenome. Blackleg-causing P. brasiliense isolates had increased genome size with high levels of prophage integration. To study the diversity and dynamics of these prophages across the pangenome, we developed an approach to trace prophages across genomes using pangenome homology group signatures. We identified lineage-specific as well as generalist bacteriophages infecting Pectobacterium species. Our results capture the ongoing dynamics of mobile genetic elements, even in the clonal lineages. The observed lineage-specific prophage dynamics provide mechanistic insights into Pectobacterium pangenome growth and contribution to the radiating lineages of P. brasiliense.

Genomic, transcriptomic and metabolomic analyses of Amorphophallus albus provides insights into the evolution and resistance to southern blight pathogen

Introduction

Amorphophallus albus, a perennial herb in the Araceae family, is a valuable cash crop known for its high production of konjac glucomannan and high disease resistance.

Methods

In this study, we present a high-quality, chromosome-scale genome assembly of A. albus using a combination of PacBio HiFi sequencing, DNBSEQ short-read sequencing, and Hi-C technology. To elucidate the molecular mechanisms underlying southern blight resistance, we performed an integrated analysis of transcriptomic and metabolomic profiles across three infection stages of A. albus.

Results and discussion

Here, we assembled and annotated the complete genome of A. albus, providing a chromosome-level assembly with a total genome size of 5.94 Gb and a contig N50 of 5.61 Mb. The A. albus genome comprised 19,908 gene families, including 467 unique families.The slightly larger genome size of A. albus compared to A. konjac may have been affected by a recent whole-genome duplication event. Transcriptional and metabolic analyses revealed significant enrichment of differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) involved in phenylpropanoid biosynthesis, plant hormone signal transduction, phenylalanine metabolism, and the biosynthesis of phenylalanine, tyrosine, and tryptophan. These findings not only advance the understanding of genetic and evolutionary characteristics of A. albus but also provide a foundation for future research on the resistance mechanisms of konjac against southern blight disease.

The endophytic fungal community plays a crucial role in the resistance of host plants to necrotic bacterial pathogens

Konjac species (Amorphophallus spp.) are the only plant species in the world that are rich in a large amount of konjac glucomannan (KGM). These plants are widely cultivated as cash crops in tropical and subtropical countries in Asia, including China. Pectobacterium carotovorum subsp. carotovorum (Pcc) is one of the most destructive bacterial pathogens of konjac. Here, we analyzed the interactions between Pcc and susceptible and resistant konjac species from multiple perspectives. At the transcriptional and metabolic levels, the susceptible species A. konjac and resistant species A. muelleri exhibit similar molecular responses, activating plant hormone signaling pathways and metabolizing defense compounds such as phenylpropanoids and flavonoids to resist infection. Interestingly, we found that Pcc stress can lead to rapid recombination of endophytic microbial communities within a very short period (96 h). Under conditions of bacterial pathogen infection, the relative abundance of most bacterial communities in konjac tissue decreased sharply compared with that in healthy plants, while the relative abundance of some beneficial fungal communities increased significantly. The relative abundance of Cladosporium increased significantly in both kinds of infected konjac compared to that in healthy plants, and the relative abundance in resistant A. muelleri plants was greater than that in susceptible A. konjac plants. Among the isolated cultivable microorganisms, all three strains of Cladosporium strongly inhibited Pcc growth. Our results further elucidate the potential mechanism underlying konjac resistance to Pcc infection, highlighting the important role of endophytic microbial communities in resisting bacterial pathogen infections, especially the more direct role of fungal communities in inhibiting pathogen growth.