Kiwifruit bacterial cankers caused by Pseudomonas syringae pv. actinidiae (Psa) are a serious threat to the kiwifruit industry. Salicylic acid (SA) regulates plant defense responses and was previously found to enhance kiwifruit's resistance to Psa. However, the underlying mechanisms of this process remain unclear. In this study, we used 4D proteomics to investigate how SA enhances kiwifruit's resistance to Psa and found that both SA treatment and Psa infection induced dramatic changes in the proteomic pattern of kiwifruit. Psa infection triggered the activation of numerous resistance events, including the MAPK cascade, phenylpropanoid biosynthesis, and hormone signaling transduction. In most cases, the differential expression of a number of genes involved in the SA signaling pathway played a significant role in kiwifruit's responses to Psa. Moreover, SA treatment upregulated numerous resistance-related proteins, which functioned in defense responses to Psa, including phenylpropanoid biosynthesis, the MAPK cascade, and the upregulation of pathogenesis-related proteins. We also found that SA treatment could facilitate timely defense responses to Psa infection and enhance the activation of defense responses that were downregulated in kiwifruit during infection with Psa. Thus, our research deciphered the potential mechanisms of SA in promoting Psa resistance in kiwifruit and can provide a basis for the use of SA to enhance kiwifruit resistance and effectively control the occurrence of kiwifruit bacterial cankers.
Keywords: bacterial canker; kiwifruit plant; proteome; salicylic acid.