Diurnal and Seasonal Variation of Isoprene Biosynthesis-Related Genes in Grey Poplar Leaves

Abstract

Transcript levels of mRNA from 1-deoxy-D-xylulose 5-phosphate reductoisomerase (PcDXR), isoprene synthase (PcISPS), and phytoene synthase (PcPSY) showed strong seasonal variations in leaves of Grey poplar (Populus 3 canescens [Aiton] Sm.). These changes were dependent on the developmental stage and were strongly correlated to temperature and light. The expression rates of the genes PcDXR and PcISPS were found to be significantly correlated to each other, whereas the expression of the PcPSY gene showed a different seasonal pattern. Protein concentration and enzyme activity of PcISPS showed distinct seasonal patterns peaking in late summer, whereas highest transcription levels of PcISPS were observed in early summer. Moreover, correlation between PcISPS protein concentration and enzyme activity changed, in particular in autumn, when PcISPS protein levels remained high while enzyme activity declined, indicating posttranslational modifications of the enzyme. The positive correlation between dimethylallyl diphosphate levels and PcISPS protein content was found to be consistent with the demonstrated synchronized regulation of PcDXR and PcISPS, suggesting that metabolic flux through the 1-deoxy-D-xylulose 5-phosphate pathway and isoprene emission capacity are closely intercoordinated. Transcript levels of PcISPS showed strong diurnal variation with maximal values before midday in contrast to PcDXR, whose gene expression exhibited no clear intraday changes. During the course of a day, in vitro PcISPS activities did not change, whereas leaf dimethylallyl diphosphate levels and isoprene emission showed strong diurnal variations depending on actual temperature and light profiles on the respective day. These results illustrate that the regulation of isoprene biosynthesis in Grey poplar leaves seems to happen on transcriptional, posttranslational, and metabolic levels and is highly variable with respect to seasonal and diurnal changes in relation to temperature and light.

Isoprene emission from terrestrial ecosystems in response to global change: minding the gap between models and observations

“…Past studies have shown that I s can be regulated up or down depending on recent day-to-day weather patterns (Sharkey et al 1999;Geron et al 2000;Pétron et al 2001), and even within a single day (Geron et al 2000;Mayrhofer et al 2005). Although it is somewhat anecdotal, we observed a 26% increase in I s during the 2 days of extremely hot weather that occurred during the Aspen FACE campaign.…”

Circadian Rhythms of Isoprene Biosynthesis in Grey Poplar Leaves

“…A recent study in poplar (Populus spp.) shows partial correlation of ISPS gene expression and enzyme activity during the season (Mayrhofer et al, 2005). Diurnal variations of PcISPS and PcDXR (Mayrhofer et al, 2005) gene expression were also reported, expression peaking in the morning for PcISPS and in the afternoon for PcDXR.…”

“…shows partial correlation of ISPS gene expression and enzyme activity during the season (Mayrhofer et al, 2005). Diurnal variations of PcISPS and PcDXR (Mayrhofer et al, 2005) gene expression were also reported, expression peaking in the morning for PcISPS and in the afternoon for PcDXR. However, no information exists on the factors responsible for these diurnal changes and whether circadian components are involved in that regulation.…”

“…Because we observed circadian regulation of the level of transcript for PcISPS, we wanted to check whether these variations were also present at the level of PcISPS protein concentration, activity, and, finally, emission of isoprene, knowing that emission shows daily variations under day-night cycles (Mayrhofer et al, 2005).…”

Process-based simulation of seasonality and drought stress in monoterpene emission models

“…One is the respective routine of the MEGAN model Müller et al, 2008), which applies an empirical adjustment based on the past 10 days of light and temperature to calculate emissions, and the other is the SIM model that derives the seasonal course of the isoprenoid forming enzyme activity, which is closely related to potential emission, explicitly from the previous days climatic conditions (Lehning et al, 2001). Only the latter model reflects the finding that seasonal changes in enzyme activity result from physiological production and destruction processes (Lehning et al, 1999;Loreto et al, 2001;Fischbach et al, 2002;Mayrhofer et al, 2005).…”