Differential gene expression in senescing leaves of two silver birch genotypes in response to elevated CO₂ and tropospheric ozone

Abstract

Long-term effects of elevated CO2 and O3 concentrations on gene expression in silver birch (Betula pendula Roth) leaves were studied during the end of the growing season. Two birch genotypes, clones 4 and 80, with different ozone growth responses, were exposed to 2¥ ambient CO2 and/or O3 in open-top chambers (OTCs). Microarray analyses were performed after 2 years of exposure, and the transcriptional profiles were compared to key physiological characteristics during leaf senescence. There were genotypic differences in the responses to CO2 and O3. Clone 80 exhibited greater transcriptional response and capacity to alter metabolism, resulting in better stress tolerance. The gene expression patterns of birch leaves indicated contrasting responses of senescence-related genes to elevated CO2 and O3. Elevated CO2 delayed leaf senescence and reduced associated transcriptional changes, whereas elevated O3 advanced leaf senescence because of increased oxidative stress. The combined treatment demonstrated that elevated CO2 only temporarily alleviated the negative effects of O3. Gene expression data alone were insufficient to explain the O3 response in birch, and additional physiological and biochemical data were required to understand the true O3 sensitivity of these clones.

High CO2 primes plant biotic stress defences through redox-linked pathways

“…However, most evidence suggests that high CO 2 does not accelerate senescence. For instance, senescenceassociated genes were repressed by high CO 2 in poplar, in contrast to the effect of oxidative stress triggered by ozone exposure (Kontunen-Soppela et al, 2010). In our study, the activation of defense pathways was not accompanied by increases in SAG12 transcripts.…”

Apoplastic Reactive Oxygen Species Transiently Decrease Auxin Signaling and Cause Stress-Induced Morphogenic Response in Arabidopsis

“…Chronic exposure to elevated O 3 causes biochemical changes, reduced growth, and morphological changes in several plant species (Skärby et al, 2004;Li et al, 2006;Karnosky et al, 2007;Kontunen-Soppela et al, 2010;Street et al, 2011). Similarly, chronic exposure to several other stresses causes similar growth changes.…”

Cellular and Molecular Mechanisms for Elevated CO2–Regulation of Plant Growth and Stress Adaptation

“…Elevated CO 2 mainly leads to the up-regulation of a large number of genes controlling cell division and cell growth ( Fig. The activity of xyloglucan endotransglycosylase/hydrolase increased with elevated CO 2 (550 to 640 vs. 330 to 350 mmol mol -1 ; Ranasinghe and Taylor, 1996;Ferris et al, 2001), while the β-xylosidase catalyzing hemicellulose metabolism in secondary cell walls was down-regulated (625 to 775 vs. 350 to 400 mmol mol -1 ; Kontunen-Soppela et al, 2010b). Among the many genes responsive to elevated CO 2 , upregulation of genes involved in cell-wall loosening and cell-expansion were consistently found in leaves of various plant species (De Souza et al, 2008;Druart et al, 2006;Gupta et al, 2005;Kim et al, 2006;Taylor et al, 2006;Wei et al, 2013).…”

“…Several genes involved in light harvesting were down-regulated by elevated CO 2 (550 to 780 vs. 280 to 380 mmol mol -1 ) in various plants species, such as chlorophyll a-b binding protein (a core antenna protein for light harvesting), Cytochrome b6/f complex, PSI reaction center subunit XI, PSI light-harvesting gene 5, PSI light-harvesting gene 4, PSII light-harvesting complex gene 1.4, PSII light-harvesting complex gene 2.3, and PSII subunit Q and X (PSII subunit optimize the oxygen evolution reaction by regulating the binding properties of the essential cofactors Ca 2+ and Cl -; Table S3; Cseke et al, 2009;Kim et al, 2006;Kontunen-Soppela et al, 2010b;Leakey et al, 2009;Li et al, 2008;Takatani et al, 2014). Several genes involved in light harvesting were down-regulated by elevated CO 2 (550 to 780 vs. 280 to 380 mmol mol -1 ) in various plants species, such as chlorophyll a-b binding protein (a core antenna protein for light harvesting), Cytochrome b6/f complex, PSI reaction center subunit XI, PSI light-harvesting gene 5, PSI light-harvesting gene 4, PSII light-harvesting complex gene 1.4, PSII light-harvesting complex gene 2.3, and PSII subunit Q and X (PSII subunit optimize the oxygen evolution reaction by regulating the binding properties of the essential cofactors Ca 2+ and Cl -; Table S3; Cseke et al, 2009;Kim et al, 2006;Kontunen-Soppela et al, 2010b;Leakey et al, 2009;Li et al, 2008;Takatani et al, 2014).…”