Silencing two herbivory-activated MAP kinases, SIPK and WIPK, does not increase Nicotiana attenuata's susceptibility to herbivores in the glasshouse and in nature

Salicylic acid-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK) are activated by Manduca sexta attack and elicitors to mediate defense signaling in Nicotiana attenuata. Here, the ecological consequences of SIPK and WIPK silencing for N. attenuata's resistance to M. sexta and its other native herbivores were analyzed. Stably transformed plants with reduced expression of NaSIPK (irNaSIPK) and NaWIPK(irNaWIPK) were generated and characterized in field and glasshouse experiments. Both irNaSIPK and irNaWIPK plants had reduced direct and indirect defenses but were not particularly susceptible in nature. In the glasshouse, M. sexta larvae consumed less and gained the same mass on irNaSIPK and irNaWIPK as on wild-type (WT) plants. Green leaf volatile (GLV) emission was highly attenuated in irNaSIPK and irNaWIPK plants, and complementation with synthetic GLVs increased M. sexta performance. To test the hypothesis that reduced GLV emissions account for the lack of herbivory phenotype, GLV emissions were attenuated by silencing NaHPL in jasmonate-deficient plants (asNaLOX3), which are highly susceptible to herbivores. Reducing GLV emissions in asNaLOX3 plants 'rescued' these plants from being heavily damaged by M. sexta. GLV emissions in irNaSIPK and irNaWIPK plants may compensate for the impaired defenses of NaSIPK-and NaWIPK-silenced plants in nature by reducing their apparency to herbivores.