Impact of mitochondrial alternative oxidase expression on the response of Nicotiana tabacum to cold temperature

Abstract

The plant mitochondrial electron transport chain (ETC) includes a non-energy conserving alternative oxidase (AOX) thought to dampen reactive oxygen species (ROS) generation by the ETC and/or facilitate carbon metabolism by uncoupling it from ATP turnover. When wild-type (WT) Nicotiana tabacum grown at 28°C/22°C (light/dark) were transferred to 12°C/5°C, they showed a large induction of leaf Aox1a mRNA and AOX protein within 24 h. Transfer to cold also resulted in a large accumulation of monosaccharides, an increase in transcript level of genes encoding important ROS-scavenging enzymes and a moderate increase in lipid peroxidation. Transgenic plants with suppressed AOX level showed less cold-induced sugar accumulation than WT while transgenic plants with enhanced AOX levels showed enhanced sugar accumulation. This is inconsistent with the hypothesis that AOX acts to burn excess carbohydrate, but rather suggests a role for AOX to aid sugar accumulation, at least during cold stress. At 28°C/22°C, plants with suppressed AOX had elevated levels of lipid peroxidation compared with WT, while plants with enhanced AOX had reduced lipid peroxidation. This is consistent with the hypothesis that AOX dampens ROS generation and oxidative damage. However, this inverse relationship between AOX level and lipid peroxidation did not hold upon shift to cold. Under this stress condition, plants with strong suppression of AOX show enhanced induction of ROS-scavenging enzymes compared with WT and decline in lipid peroxidation. These data suggest that, under stress conditions, the lack of AOX enhances a mitochondrial stress-signaling pathway able to increase the ROS-scavenging capacity of the cell.

Mitochondrial Alternative Oxidase Maintains Respiration and Preserves Photosynthetic Capacity during Moderate Drought in Nicotiana tabacum

“…1). This correlates well with our previous studies showing that RI29 is the stronger of the two knockdowns (Wang et al, 2011;Wang and Vanlerberghe, 2013;Cvetkovska et al, 2014). In RI29, the effects of drought on A n , ETR II , excitation pressure, F PSII , and NPQ were all strongly magnified relative to the wild type, whereas RI9 (the slightly weaker AOX knockdown) always showed an intermediate response between RI29 and the wild type (Figs.…”

“…Transgenic plant lines with suppressed levels of AOX protein (RI9 and RI29) attributable to the presence of an AOX1a RNA interference construct, or elevated levels of AOX protein (B7) due to the presence of an AOX1a transgene driven by a constitutive promoter were previously described (Wang et al, 2011;Wang and Vanlerberghe, 2013;Cvetkovska et al, 2014). In particular, it has been shown that AOX protein levels are strongly suppressed in the knockdowns, even under the strongly AOX-inducing conditions of low temperature (Wang et al, 2011) or severe drought (Wang and Vanlerberghe, 2013). Seeds were germinated in vermiculite for 16 d and then transferred individually to 4-inch plastic pots containing a general purpose growing medium with 4 parts soil (Promix BX; Premier Horticulture) and 1 part vermiculite.…”

Overexpression of an alternative oxidase gene, OsAOX1a, improves cold tolerance in Oryza sativa L.

“…Furthermore, the short time (hours) of the cold treatment did not affect lipid peroxidation rates between wildtype and NtAOX1 overexpressing plants. This result does not conflict with the primary role of AOX1 as an ROS scavenger under long periods of cold growth (Wang et al, 2011). After all, the ROS accumulation mechanism and mitochondrial respiration response are distinct between transient and steady stress.…”

“…Overexpressing AtAOX1 produced better shoot growth at 12°C, whereas shoot growth was significantly inhibited in knockdown plants compared to wild types (Fiorani et al, 2005). In addition, biochemical and molecular changes were also observed in tobacco plants with suppressed or constitutively expressed NtAOX1a, although growth performance was not mentioned (Wang et al, 2011). On the other hand, increasing evidence from different plant species has indicated that the expression of AOX1 or the activity of AOX might be induced by low temperatures, as well as by drought or other abiotic stresses.…”

“…Furthermore, other evidence has suggested that overexpression of AOX1 could increase stress tolerance ability by generating less ROS (Vanlerberghe et al, 2009). However, most of these genetics studies were performed on the dicot plants Arabidopsis thaliana and Nicotiana tabacum or on species with unique physiological processes (Wang et al, 2011;Zidenga et al, 2012). Therefore, the function of AOX1 in monocot rice remains largely unknown.…”