A patatin-like protein synergistically regulated by jasmonate and ethylene signaling pathways plays a negative role in Nicotiana attenuata resistance to Alternaria alternata

Although patatin was initially identified as a major storage protein in potato tubers, patatin-like proteins (PLPs) have been recently reported to be widely present in many plant species and shown to be involved in plant-pathogen interactions. However, it is not clear whether PLPs are involved in Nicotiana attenuata resistance against the necrotrophic fungal pathogen, Alternaria alternata. In this study we identified a NaPLP gene, whose expression was highly elicited by A. alternata inoculation. Silencing NaPLP enhanced N. attenuata resistance to A. alternata, which was associated with higher induction levels of JA and ethylene biosynthetic genes, NaACS1, NaACO1 and NaLOX3. The induction of NaPLP expression by the fungus was abolished in JA-deficient plants and significantly reduced in ethylene-insensitive plants. In addition, NaPLP transcripts were highly induced by exogenous treatment with either methyl jasmonate (MeJA) or ethephon. Co-treatment with MeJA and ethephon led to a much higher induction level of NaPLP transcripts, and this synergistic induction was largely dependent on endogenous JA and ethylene signaling pathways. Thus, we conclude that the NaPLP gene is elicited by A. alternata via JA and ethylene signaling pathways in a synergistic way; however, unlike other JA- and ethylene-induced defense genes, NaPLP negatively affects plant resistance to the fungus likely by suppressing JA and ethylene biosynthetic gene expression.