Enhanced Low Oxygen Survival in Arabidopsis through Increased Metabolic Flux in the Fermentative Pathway

Abstract

We manipulated the enzyme activity levels of the alcohol fermentation pathway, pyruvate decarboxylase (PDC), and alcohol dehydrogenase (ADH) in Arabidopsis using sense and antisense overexpression of the corresponding genes (PDC1, PDC2, and ADH1). Transgenic plants were analyzed for levels of fermentation and evaluated for changes in hypoxic survival. Overexpression of either Arabidopsis PDC1 or PDC2 resulted in improved plant survival. In contrast, overexpression of Arabidopsis ADH1 had no effect on flooding survival. These results support the role of PDC as the control step in ethanol fermentation. Although ADH1 null mutants had decreased hypoxic survival, attempts to reduce the level of PDC activity enough to see an effect on plant survival met with limited success. The combination of flooding survival data and metabolite analysis allows identification of critical metabolic flux points. This information can be used to design transgenic strategies to improve hypoxic tolerance in plants.Plants are constantly challenged by environmental stresses that reduce crop yield (e.g. salinity, low temperature, drought, and flooding). Soils with excess water account for 15.7% of the arable land in the United States, and flooding accounted for 16.4% of the crop insurance claims, making it the second highest cause of crop loss in the United States (Boyer, 1982). Traditionally, plant breeders have selected directly for increased stress tolerance, however, selection for flooding tolerance has been performed only in rice (Oryza sativa), where a genetic mapping approach was used to identify major and minor genes involved in submergence tolerance (Sripongpangkul et al., 2000; Xu et al., 2000). Transgenic plants with increased tolerance to drought, salinity, low temperatures, or a combination of these stresses (Nelson et al., 1998; Huang et al., 2000) were obtained by introducing genes for the overaccumulation of benign compounds (e.g. Gly betaine, mannitol, and Pro) that are believed to act as osmolytes. Other groups have increased stress tolerance in Arabidopsis by overexpressing transcription factors (Jaglo-Ottosen et al., 1998; Kasuga et al., 1999; Yamaguchi-Shinozaki and Shinozaki, 2001) or signal transduction components (Piao et al., 2001; Tamminen et al., 2001).There is substantial variation among terrestrial crop species in their ability to tolerate waterlogging conditions. Even rice, which is adapted to life in a flooded environment, incurs damage if the shoots are completely submerged for periods of time (Drew, 1997; Quimio et al., 2000). Genetic variation in flooding tolerance has been found in rice, maize (Zea mays), barley (Hordeum vulgare), and Arabidopsis. In some cases, this variation results from specific mutants (Harberd and Edwards, 1982; Dolferus et al., 1985; Lemke-Keyes and Sachs, 1989; Ricard et al., 1998). Several studies have focused on the effect of overexpression of genes on flooding tolerance. Zhang et al. (2000) overexpressed a gene involved in cytokinin biosynthesis and demonstrated improve...

Arabidopsis CML38, a Calcium Sensor That Localizes to Ribonucleoprotein Complexes under Hypoxia Stress

“…These findings confirm previous work that has placed CML38 into the small group of core hypoxia-response genes (Mustroph et al, 2009) and suggest that CML38 may play a specialized role as a calcium sensor during this response. Mutations that target core hypoxia-response genes in general result in a lower survival and/or increased sensitivity to anaerobic stress (Ismond et al, 2003;Kürsteiner et al, 2003;Licausi et al, 2010;Giuntoli et al, 2014;Sorenson and Bailey-Serres, 2014). To determine the effects of the elimination of CML38 expression on Arabidopsis survival to anaerobic stress, a transfer DNA (T-DNA) mutant (Salk_066538C; referred to here as cml38) line with an insertion site within the coding region of CML38 (Supplemental Fig.…”

The Heat-Inducible Transcription Factor HsfA2 Enhances Anoxia Tolerance in Arabidopsis

“…Arabidopsis plants devoid of alcohol dehydrogenase (ADH) or Suc synthases are less tolerant to anoxia, although an increased expression of ADH cannot confer enhanced anoxia tolerance (Ismond et al, 2003;Bieniawska et al, 2007). Overexpression of pyruvate decarboxylase, catalyzing a rate-limiting step in ethanol fermentation, has been shown to increase Arabidopsis survival (Ismond et al, 2003).…”

Plant respiration under low oxygen

“…Evaluation in Arabidopsis mutants has indicated that overexpression of PCD and ADH promotes stress tolerance during oxygen deficiency, because the carbon flux is controlled through alcoholic fermentation and through the lactate and alanine pathways (KatoNoguchi and Morokuma, 2007). Nevertheless, additional information about the special features associated with fermentative pathways, and specifically alcoholic fermentation, where the absence of oxygen would not be responsible for inducing enzymes such as PCD and ADH, is highly desirable (Kennedy et al, 1992;Rahman et al, 2001;Ismond et al, 2003;Kursteiner et al, 2003).…”