Isoenzyme replacement of glucose-6-phosphate dehydrogenase in the cytosol improves stress tolerance in plants

Abstract

In source leaves of resistant tobacco, oxidative burst and subsequent formation of hypersensitive lesions after infection with Phytophthora nicotianae was prevented by inhibition of glucose-6-phosphate dehydrogenase (G6PDH) or NADPH oxidases. This observation indicated that plant defense could benefit from improved NADPH availability due to increased G6PDH activity in the cytosol. A plastidic isoform of the G6PDH-encoding gene, G6PD, displaying high NADPH tolerance was engineered for cytosolic expression (cP2), and introduced into a susceptible cultivar. After infection, transgenic (previously susceptible) lines overexpressing cP2 showed early oxidative bursts, callose deposition, and changes in metabolic parameters. These responses resulted in timely formation of hypersensitive lesions similar to resistant plants, although their extent varied considerably between different transgenic lines. Additional RNAi suppression of endogenous cytosolic G6PD isoforms resulted in highly uniform defense responses and also enhanced drought tolerance and flowering. Cytosolic G6PDH seems to be a crucial factor for the outcome of plant defense responses; thus, representing an important target for modulation of stress resistance. Because isoenzyme replacement of G6PDH in the cytosol was beneficial under various kinds of cues, we propose this strategy as a tool to enhance stress tolerance in general.oxidative burst ͉ source-to-sink transition ͉ NADPH availability ͉ pathogen resistance ͉ tobacco P lants are under continuous threat of being challenged by pathogenic microorganisms, which try to exploit them as a source of carbohydrates and other assimilates. Timely recognition of invading microorganisms and rapid and effective induction of defense responses are presently considered the main difference between pathogen-resistant and susceptible plant lines (1). So-called compatible interactions between pathogens and plants result if the pathogen can overcome plant defense barriers and establish disease symptoms. During an incompatible interaction, a wealth of defense mechanisms [e.g., generation of reactive oxygen species (ROS), synthesis of pathogenesis-related (PR) proteins, cell-wall fortification, and the hypersensitive reaction (HR)] can efficiently limit pathogen growth. The HR, which includes ROS formation and programmed cell death (PCD), represents the most efficient mechanism of plant defense. ROS were previously proposed to orchestrate the establishment of plant defense responses (2, 3). NADPH oxidases at the plasma membrane are considered the main source of extracellular ROS formation during defense, the so-called oxidative burst. Down-regulation or elimination of NADPH oxidase leads to suppression of pathogen-induced oxidative bursts and HR (4).The oxidative burst, an evolutionarily conserved mechanism, is part of the innate immune response, and (besides triggering plant PCD) it is thought to contribute to direct killing of invading microorganisms. It also helps to mount an invasion barrier through radical-mediated polymer...

Defects in Peroxisomal 6-Phosphogluconate Dehydrogenase Isoform PGD2 Prevent Gametophytic Interaction in Arabidopsis thaliana

“…The latter are accompanied by rapid stomata closure and the inhibition of photosynthesis (Katsir et al, 2008;Campos et al, 2014;Wasternack, 2014). In tobacco leaves, this leads to callose-induced Suc retention (source-to-sink transition), which is needed for the defense of the infected tissue (Scharte et al, 2009).…”

“…The genomic gPGD2 fragment was inserted into EcoRV-opened pBluescript SK and cloned in E. coli XL1 blue (Stratagene). The genomic fragment was released with SmaI and SalI and inserted into binary vector pGSC1704-HygR via SnaBI and SalI, cloned in E. coli XL1 blue, and retransformed into Agrobacterium tumefaciens strain GV2260 as described by Scharte et al (2009). Floral dip transformation of heterozygous plants was conducted as described by Clough and Bent (1998).…”

Overcompensation in Response to Herbivory in Arabidopsis thaliana: The Role of Glucose-6-Phosphate Dehydrogenase and the Oxidative Pentose-Phosphate Pathway

“…The OPPP is a primary source of the reductant NADPH for biosynthetic processes such as the assimilation of nitrogen into amino acids, fatty-acid synthesis, and resistance to oxidative damage. Intermediates, such as ribose-5-phosphate, are also withdrawn from the OPP pathway for phenylpropanoid production via the shikimate pathway (Figure 4) (Kruger and Von Schaewen 2003;Scharte et al 2009).…”

“…Initially, following apical damage, the G6PDH1 gene elicits a suite of defensive reactions that are likely associated with cellular damage from herbivory. These may include reactive oxygen species to ward off infection and induced chemical defenses, such as glucosinolates, via the shikimate pathway (Scharte et al 2009). When analyzing genes that were significantly differentially expressed (from our microarray data), several of the genes affected were found to be enzymes (e.g., a suite of invertase genes, G6PDH1, and galactinol synthase) involved in carbohydrate metabolism, and these genes were significantly up-regulated and likely play a significant role in overcoming tissue loss.…”

An Overview of Plant Photosynthesis Modulation by Pathogen Attacks

“…Berger et al (Berger et al, 2007) have recently reviewed how plant physiology meets phytopathology. The reader can also get more detail on this topic in previous study (Trotta et al, 2011, Essmann et al, 2008, Scharte et al, 2009). Here, we will focus our review on current knowledge on the process of higher plant photosynthesis, its outcome for both plants and fungal pathogens, the roles for some of the metabolites and transduction pathways that are implicated in this twined inter-relationship as well as the potential targets as future strategy.…”