PFLP-Intensified Disease Resistance Against Bacterial Soft Rot Through the MAPK Pathway in PAMP-Triggered Immunity

Bacterial soft rot is a devastating disease affecting a variety of vegetable crops worldwide. One strategy for controlling this disease could be the ectopic expression of the plant ferredoxin-like protein (pflp) gene. PFLP was previously shown to intensify pathogen-associated molecular pattern-triggered immunity (PTI), an immune response triggered, for example, by the flagellin epitope flg22. To gain further insight into how PFLP intensifies PTI, flg22 was used as an elicitor in Arabidopsis thaliana. First, PFLP was confirmed to intensify the rapid generation of H₂O₂, callose deposition, and the hypersensitive response when coinfiltrated with flg22. This response correlated with increased expression of the FLG22-induced receptor kinase 1 gene, which is part of the mitogen-activated protein kinase (MAPK) pathway. Although the increased response to flg22 alone did not depend on the MAPK pathway genes MEKK1, MKK5, and MPK6, the protective effect of PFLP decreased when plants mutated in these genes were inoculated with Pectobacterium carotovorum subsp. carotovorum. Furthermore, expression of PR1 and PDF1.2 also increased upon treatment with flg22 in the presence of PFLP. Taken together, these results suggest that activation of the MAPK pathway contributes to the increased resistance to bacterial soft rot observed in plants treated with PFLP.