Enhanced Methanol Production in Plants Provides Broad Spectrum Insect Resistance

Abstract

Plants naturally emit methanol as volatile organic compound. Methanol is toxic to insect pests; but the quantity produced by most of the plants is not enough to protect them against invading insect pests. In the present study, we demonstrated that the over-expression of pectin methylesterase, derived from Arabidopsis thaliana and Aspergillus niger, in transgenic tobacco plants enhances methanol production and resistance to polyphagous insect pests. Methanol content in the leaves of transgenic plants was measured using proton nuclear spectroscopy (1H NMR) and spectra showed up to 16 fold higher methanol as compared to control wild type (WT) plants. A maximum of 100 and 85% mortality in chewing insects Helicoverpa armigera and Spodoptera litura larvae was observed, respectively when fed on transgenic plants leaves. The surviving larvae showed less feeding, severe growth retardation and could not develop into pupae. In-planta bioassay on transgenic lines showed up to 99 and 75% reduction in the population multiplication of plant sap sucking pests Myzus persicae (aphid) and Bemisia tabaci (whitefly), respectively. Most of the phenotypic characters of transgenic plants were similar to WT plants. Confocal microscopy showed no deformities in cellular integrity, structure and density of stomata and trichomes of transgenic plants compared to WT. Pollen germination and tube formation was also not affected in transgenic plants. Cell wall enzyme transcript levels were comparable with WT. This study demonstrated for the first time that methanol emission can be utilized for imparting broad range insect resistance in plants.

Tuning of pectin methylesterification: consequences for cell wall biomechanics and development

“…This response was brought about by the high pH of caterpillar oral secretions. In all cases where PME activity increases in response to a biotic interaction, the methanol released by PME activity can act as a signaling molecule to the plant that is being attacked, and potentially neighboring plants (von Dahl et al 2006;Körner et al 2009;Dorokhov et al 2012;Dixit et al 2013;Komarova et al 2014). In the case of caterpillar feeding on Nicotiana attenuata, the release of methanol was significantly reduced in plants lacking a PME inducible by caterpillar oral secretions, and showed a lower expression of toxic defense proteins (Körner et al 2009).…”

“…It was also reported, however, that methanol treatment of Nicotiana attenuata reduced the level of defensive proteins when the methanol quantities were similar to those produced in response to herbivore attacks, and that larvae on methanoltreated plants gained more weight by feeding than did larvae on untreated plants (von Dahl et al 2006). When PMEs were overexpressed in tobacco and methanol production thereby increased, the plants became more resistant to aphids, whiteflies, and two species of caterpillars (Dixit et al 2013), possibly as a direct effect of methanol toxicity.…”

Overexpression of INCREASED CAMBIAL ACTIVITY, a putative methyltransferase, increases cambial activity and plant growth

“…Methanol is known to induce the expression of certain PMEs (Ramírez et al ) as observed in this study (Figure ). As the upregulated expression of PMEs could be linked to increase methanol emission (Dorokhov et al ; Dixit et al ), we hypothesize that this positive feedback regulation can contribute to maintain high PME expression and methanol emission in 35S::ICA . Interestingly, we observed increased stem elongation and radial thickening of inflorescence stems in Col‐0 co‐cultured with 35S::ICA compared with monocultured Col‐0 (Figure ).…”

“…Because methanol is emitted through the stomata on the leaf as a volatile organic compound (VOC) (Nemecek‐Marshall et al ; Hüve et al ), it is possible that methanol affects neighboring plants as well as the methanol‐producing plant itself. High PME activity induced by pathogen challenge releases more methanol, leading to increased pathogen resistance in the plant being attacked and eventually in neighboring plants (Peñuelas et al ; Körner et al ; Dorokhov et al ; Dixit et al ). It is also plausible that methanol can act as a signaling molecule for the detection of growing plants nearby as methanol emission is closely dependent on the growth rate of leaves (MacDonald and Fall ; Hüve et al ).…”

A novel pilin subunit from Xenorhabdus nematophila, an insect pathogen, confers pest resistance in tobacco and tomato

“…The transgenic plants expressing the insecticidal Bacillus thuringiensis (Bt) toxins have been successfully developed to kill some key insect pests since several years for reducing both yield loss and pesticide utilization, consequently mitigating environmental and human health hazards (Shelton et al 2002;Christou et al 2006;Brookes and Barfoot 2009;Naranjo 2011;Dixit et al 2013). Intensive cultivation of Bt crops increases the concern about resistance development in insect pests to crystal protein toxins of B. thuringiensis (Bravo and Soberon 2008;Tabashnik et al 2008) and has fuelled vigorous efforts for exploring new insecticidal proteins.…”