-3-Oxo-Octanoyl Homoserine Lactone Primes Plant Resistance Against Necrotrophic Pathogen by Coordinating Jasmonic Acid and Auxin-Signaling Pathways.

Many Gram-negative bacteria use small signal molecules, such as -acyl-homoserine lactones (AHLs), to communicate with each other and coordinate their collective behaviors. Recently, increasing evidence has demonstrated that long-chained quorum-sensing signals play roles in priming defense responses in plants. Our previous work indicated that a short-chained signal, -3-oxo-octanoyl homoserine lactone (3OC8-HSL), enhanced Arabidopsis resistance to the hemi-biotrophic bacteria pv. DC3000 through priming the salicylic acid (SA) pathway. Here, we found that 3OC8-HSL could also prime resistance to the necrotrophic bacterium ssp. () through the jasmonic acid (JA) pathway, and is dependent on auxin responses, in both Chinese cabbage and Arabidopsis. The subsequent invasion triggered JA accumulation and increased the down-stream genes' expressions of JA synthesis genes (, , and ) and JA response genes ( and ). The primed state was not observed in the Arabidopsis - and mutants, which indicated that the primed resistance to was dependent on the JA pathway. The 3OC8-HSL was not transmitted from roots to leaves and it induced indoleacetic acid (IAA) accumulation and the and auxin-responsive genes' expressions in seedlings. When Arabidopsis and Chinese cabbage roots were pretreated with exogenous IAA (10 μM), the plants had activated the JA pathway and enhanced resistance to , which implied that the JA pathway was involved in AHL priming by coordinating with the auxin pathway. Our findings provide a new strategy for the prevention and control of soft rot in Chinese cabbage and provide theoretical support for the use of the quorum-sensing AHL signal molecule as a new elicitor.