Gene regulation in plant herbivory defense : deffect of insect mechanical wounding and chemical oral secretion factors

To study the different roles of mechanical wounding and chemical elicitors caused by insect feeding on plant in regulating plant responses, gene regulation of Arabidopsis thaliana leaves after insect (Plutella xylostella) feeding and sole mechanical wounding (MecWorm) was investigated by whole genome microarray analysis of wounded and systemic leaves. Genes could be assigned to four different types of gene regulation induction: Induced only by (i) chemical or (ii) mechanical factors, induced by mechanical wounding but (iii) changed significantly or (iv) suppressed by chemical factors. Analysis of the gene related pathways showed that after insect feeding, damaged leaves are the direct battle field against insect attack. Plants react by reducing photosynthesis and cell reproduction and shift their major activities in the damaged leaves to defense. Systemic leaves conduct resources production for plant recovery and defense with powerful signaling and communication. In plant-insect interaction gene regulation, mechanical wounding is the major trigger, while chemical factors are fine tuners for a more efficient and biotic stress focused defense machinery. To mimic insect feeding more precisely, both mechanically and chemically, ‘SpitWorm’ was developed based on MecWorm. For the proof of concept delivery speed and dilution of oral secretion of Spodoptera littorals was optimized. By comparing regulation of JA responsive genes and induced volatile emissions of lima bean (Phaseolus lunatus) leaves damaged by S. littoralis, MecWorm, and SpitWorm, it could be shown that SpitWorm is able to induce a volatile bouquet almost identical to herbivory induction, qualitatively and quantitatively and induced a gene regulation pattern identical to S. littoralis feeding.