Andersen, M. T. | bioRxiv Science

bioRxiv2022

The complete genome sequence of Pseudomonas syringae pv. actinidifoliorum ICMP 18803

The complete genome of Pseudomonas syringae pv. actinidifoliorum ICMP18803 (Pfm) was sequenced using the Oxford Nanopore minION platform to an average read depth of 123. The genome assembled into a single chromosome of 6,353,853 bp after error-correction with Illumina short reads using Pilon. The complement of effector genes from a P. syringae pathovar plays the predominant role in defining its pathogenicity. Automatic gene annotation pipelines often poorly identify and name effector genes, however. Despite Pfm being a relatively weak pathogen of kiwifruit, a set of 31 effectors, 26 of which were full length, was identified by mapping the comprehensive effector library generated by Dillon et al. (2019). The Pfm genome with the effector complement, correctly named and annotated was resubmitted to Genbank (CP081457).

genomics↗

bioRxiv2021

Effector loss drives adaptation of Pseudomonas syringae pv. actinidiae to Actinidia arguta

A pandemic isolate of Pseudomonas syringae pv. actinidiae biovar 3 (Psa3) has devastated kiwifruit orchards growing cultivars of Actinidia chinensis. In contrast, A. arguta (kiwiberry) is resistant to Psa3. This resistance is mediated via effector-triggered immunity, as demonstrated by induction of the hypersensitive response in infected A. arguta leaves, observed by microscopy and quantified by ion-leakage assays. Isolates of Psa3 that cause disease in A. arguta have been isolated and analyzed, revealing a 49 kb deletion in the exchangeable effector locus (EEL). This natural EEL-mutant isolate and strains with synthetic knockouts of the EEL were more virulent in A. arguta plantlets than wild-type Psa3. Screening of a complete library of Psa3 effector knockout strains identified increased growth in planta for knockouts of four effectors - AvrRpm1a, HopF1c, HopZ5a, and the EEL effector HopAW1a - suggesting a resistance response in A. arguta. Hypersensitive response (HR) assays indicate that three of these effectors trigger a host species-specific HR. A Psa3 strain with all four effectors knocked out escaped host recognition, but a cumulative increase in bacterial pathogenicity and virulence was not observed. These avirulence effectors can be used in turn to identify the first cognate resistance genes in Actinidia for breeding durable resistance into future kiwifruit cultivars.

plant biology↗