Actinidia-Pseudomonas syringae pv. actinidiae interaction: differentially expressed plant transcripts during infection

Since 2008, kiwifruit bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) has spread to pandemic scale. In order to elucidate the molecular events of the kiwifruit-Psa interaction, Illumina RNAseq was conducted after Psa inoculation and mock inoculation, on both acibenzolar-S-methyl (ASM) treated and untreated Actinidia chinensis plants. De-novo assembly of the kiwifruit transcriptome revealed 39,607 transcripts. To investigate the transcriptome expression profile during the infection process, hierarchical cluster analysis was performed. During the infection process, about 3000 transcripts were modulated. It was notable that the number of modulated transcripts in infected plants were higher than in ASM-treated infected plants. Furthermore, the RNAseq technology permitted us to identify novel transcripts of unknown function but related to infection and ASM treatment. The analysis revealed that the coordinates of some important gene functional categories change, such as hormonal balance, transcriptional regulation and signalling. Different transcription factors were also linked with signalling and hormonal balance and are involved in the ability of ASM-treated plants to assemble the right defence response against Psa. On the other hand, control plants respond to Psa, but not in an adequate way to counteract the infection. Indeed, several transcripts related to plant signalling and putatively encoding RLK-LRR and PRR proteins were exclusively found under these conditions, while they were absent in ASM-treated plants, highlighting how the response of susceptible plants belongs to a separate cluster from that of ASM-treated plants.