Transgenic, non‐isoprene emitting poplars don’t like it hot

Abstract

SummaryThe physiological role of isoprene emission in plants is a matter of much debate. One of the most widely propagated hypotheses suggests a function of isoprene in the protection of leaf physiological processes against thermal and oxidative stress. To test this hypothesis, we developed transgenic Grey poplar (Populus · canescens) plants in which gene expression of isoprene synthase (ISPS) was either silenced by RNA interference (RNAi) or upregulated by over-expression of the ISPS gene. Despite increased ISPS mRNA levels, we did not observe consistent increases in isoprene emission in the over-expressing lines, indicating posttranscriptional control of ISPS by co-suppression. In the RNAi lines, levels of isoprene emission were effectively suppressed to virtually zero. Transgenic plants were subjected to temperature stress with three transient heat phases of 38-40°C, each followed by phases of recovery at 30°C. Parallel measurements of gas exchange, chlorophyll fluorescence and isoprene emission provided new insights into the physiological link between isoprene and enhanced temperature tolerance. Transgenic non-isoprene-emitting poplars showed reduced rates of net assimilation and photosynthetic electron transport during heat stress, but not in the absence of stress. The decrease in the efficiency of photochemistry was inversely correlated with the increase in heat dissipation of absorbed light energy, measured as NPQ (non-photochemical quenching). Isoprenerepressed poplars also displayed an increased formation of the xanthophyll cycle pigment zeaxanthin in the absence of stress, which can cause increased NPQ or may indicate an increased requirement for antioxidants. In conclusion, using a molecular genetic approach, we show that down-regulation of isoprene emission affects thermotolerance of photosynthesis and induces increased energy dissipation by NPQ pathways.

Isoprene in poplar emissions: effects on new particle formation and OH concentrations

“…and a well characterized transgenic line (RA22) in which gene expression of isoprene synthase (PcISPS) was knocked down by RNAi silencing (35S::PcISPS-RNAi, for further information on this line see Behnke et al, 2007). The plants were grown in the greenhouse in 2.2 L pots with soil substrate (25 % (v/v) Fruhsdorfer Einheitserde (Bayerische Gärtnereigenossenschaft, München, Germany), 25 % (v/v) silica sand (particle size 1-3 mm), 50 % (v/v) perlite (Agriperl Dämmstoff GmbH, Dortmund, Germany)), and 10 g fertilizer (Triabon (Compo, Münster, Germany): Osmocote (Scotts International B.V., Heerlen, The Netherlands), 1:1 (v/v) per L of soil) moistened with tap water.…”

“…Moreover, the potential of genetic manipulation offers the opportunity to analyze poplar mutants with different VOC emission pattern. Here, we used wild type poplars (WT) naturally emitting high rates of isoprene and transgenic lines in which isoprene emission is repressed by RNA interference (for detail see Behnke et al, 2007) to analyse differences in new particle formation potential of different natural biogenic VOC mixtures. Exposing single trees to high ozone concentrations as a proxy for pathogen-induced stress reactions (Sandermann et al, 1998) changed the emission pattern and strength significantly (Behnke et al, 2009) thus assessing a wide range of VOC compositions and their contribution to new particle formation in the absence and presence of isoprene.…”

Two Herbivore-Induced Cytochrome P450 Enzymes CYP79D6 and CYP79D7 Catalyze the Formation of Volatile Aldoximes Involved in Poplar Defense

“…To target only CYP79 mRNA, a fragment between position 310 and 534 of the coding sequence was selected. Transgenic RNAi poplar plants were amplified by micropropagation as described by Behnke et al (2007). To test the level of transgenicity, qRT-PCR analysis was done on wild-type, vector control (pCAM), and RNAi plants (line 1 and line 9) before and after wounding.…”

“…Wild-type and transgenic gray poplar (Populus 3 canescens) plants were amplified by micropropagation as described by Behnke et al (2007). Saplings of ;10-cm high were repotted to soil (Klasmann potting substrate) and propagated in a controlled environment chamber for 1 month (day, 22°C; night, 18°C; 65% relative humidity; 16-h/8-h light/dark cycle) before they were transferred to the greenhouse (day, 23 to 25°C; night, 19 to 23°C; 45 to 55% relative humidity; 16-h/8-h light/dark cycle).…”

Plant communication – why should plants emit volatile cues?

“…Herbivore induced volatiles have also been reported to protect plants against pathogens and a variety of abiotic stresses (e.g. Shulaev et al 1997;Behnke et al 2007). However, there are also many examples in which volatiles are attractive to herbivores and pathogens so that their role as repellents is far from universal (e.g.…”