Slow food: insect prey and chitin induce phytohormone accumulation and gene expression in carnivorous Nepenthes plants.
BACKGROUND AND AIMS Carnivorous Nepenthes plants use modified leaves forming pitfall traps to capture and digest prey, mainly insects, for additional nutrient supply. These traps, so called pitchers, contain a plant derived fluid composed of many hydrolytic enzymes and defence related proteins. In this study, the prey induced induction of corresponding genes of those proteins and a role for phytohormones in this process was analysed. METHODS Tissue from insect prey fed, chitin and phytohormone challenged pitchers was harvested and analysed for selected gene expressions by a quantitative PCR technique. Phytohormone levels were determined by LC MS/MS. Nepenthesin proteolytic activities were measured in the digestive fluid using a fluorescence substrate. KEY RESULTS Insect prey in the pitchers induced the accumulation of phytohormones such as jasmonates as well as the transcription of studied genes encoding a chitinase 3 and a protease (nepenthesin I) whereas a defence related protein (PR 1) gene was not induced. Treatment with chitin as a component of the insects' exoskeleton triggered the accumulation of jasmonates, the expression of nepenthesin I and chitinase 3 genes similar to jasmonic acid treatment, and induced protease activity in the fluid. All detectable responses were slowly induced. CONCLUSIONS The results suggest that upon insect prey catch a sequence of signals is initiated: (1) insect derived chitin, (2) jasmonate as endogenous phytohormone signal, (3) the induction of digestive gene expression and (4) protein expression. This resembles a similar hierarchy of events as described from plant pathogen/herbivore interactions, supporting the idea that carnivory evolved from plant defences.
Annals of botany