Increase of defense gene transcripts by cytoplasmic acidification in tobacco cell suspensions

Abstract

Cytoplasmic acidi®cation has been previously characterized as a common intracellular response of tobacco cells to elicitors (Y. Mathieu et al. 1996, Planta 199: 416±424). The possibility that cytosolic protons may activate plant defense reactions through the increased mRNA transcript levels of speci®c genes was investigated in suspension-cultured tobacco (Nicotiana tabacum L. cv. Xanthi) cells. Transcript levels of phenylalanine ammonia-lyase and 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the ®rst enzymes of phenylpropanoid and tobacco phytoalexin pathways, respectively, were quanti®ed in a variety of conditions leading to intracellular acidi®cation. Three arti®cial ways of inducing intracellular acidi®cation, acid loading, inorganic phosphate uptake and inhibition of the plasma-membrane ATPase were able to increase transcript levels of the two genes in certain conditions. The combination of two parameters of the intracellular pH decrease, intensity and duration, was shown to be crucial for the induction of the two kinds of transcript. In particular, experiments using addition of two signals showed that a cytosolic acidi®cation that was too long and/or too intense no longer allowed the increase in mRNA transcripts to occur. Together, the results indicate that cytosolic protons take part in the accumulation of the two defense gene transcripts and may be considered as one of the second messengers involved in the transduction of elicitor molecules in tobacco cells.

Are elicitins cryptograms in plant-Oomycete communications?

“…Furthermore, changes in pH have been shown to modulate the intensity of AOS production by elicited cells, and the possible regulation of the NADPH oxidase activity of plant cells by modifications of pH has been proposed [117]. In this way, cytoplasmic acidification has been reported to be involved in the complex network of cell signaling leading to defense gene activation in tobacco [140], rice [141] and Californian poppy cells [142]. A hypothetical signaling scheme which summarizes the pathways involved in the early responses of tobacco cells treated with elicitin is proposed ( fig.…”

The Gα Protein Controls a pH-Dependent Signal Path to the Induction of Phytoalexin Biosynthesis in Eschscholzia californica

“…On the other hand, an inducing effect of acidic shifts of the cytoplasmic pH was reported earlier for some pathogenesisrelated enzymes, including well-known examples from the early biosynthesis of phytoalexins as Phe ammonia lyase and hydroxymethylglutaryl-CoA reductase (i.e., the initial enzymes of phenylpropane or terpenoid metabolism, respectively) (He et al, 1998;Lapous et al, 1998). In these cases, the extra protons enter the cell from outside as indicated by the simultaneous alkalinization of the medium.…”

Elicitor-Activated Phospholipase A2 Generates Lysophosphatidylcholines That Mobilize the Vacuolar H+ Pool for pH Signaling via the Activation of Na+-Dependent Proton Fluxes

“…Prominent examples include the regulation of stomatal K ϩ channels by auxin and abscisic acid (Grabov and Blatt, 1997;Grill and Himmelbach, 1998), the gravitropic response (Scott and Allen, 1999), the control of apical growth (Feijo et al, 1999), and the induction of pathogen defense reactions in nonhost resistance (Mathieu et al, 1996;Lapous et al, 1998;Roos et al, 1998). Cytoplasmic acidification induced by biotic or abiotic stress is considered a plant-specific trigger for the synthesis of phytoalexins and other secondary metabolites (Sakano, 2001).…”

“…These events lead to complex response patterns, including hypersensitive cell death and activation or expression of antimicrobial enzymes and other pathogenesis-related proteins (Mathieu et al, 1996;Simon-Plas et al, 1997;LebrunGarcia et al, 1999). Analogous to elicitor treatment, artificial acidification of the cytoplasm caused increased mRNA levels of phenylalanine ammonia-lyase (PAL) and 3-hydroxy-3-methylglutaryl-CoA reductase (i.e., the first enzymes of the phenylpropanoid and isoprenoid pathways) in cultured cells of tobacco (Lapous et al, 1998) and of phenylalanine ammonia-lyase in rice (He et al, 1998).…”