Expression and RNA Splicing of the Maize Glutathione S-Transferase Bronze2 Gene Is Regulated by Cadmium and Other Stresses

Abstract

The Bronze2 (Bz2) gene in maize (Zea mays) encodes a glutathione S-transferase that performs the last genetically defined step in anthocyanin biosynthesis-tagging anthocyanin precursors with glutathione, allowing for recognition and entry of anthocyanins into the vacuole. Here we show that Bz2 gene expression is highly induced by heavy metals such as cadmium. Treatment of maize seedlings with cadmium results in a 20-fold increase i n 822 message accumulation and a 50-fold increase in the presence of the unspliced, intron-containing transcript. The increase in message levels during cadmium stress appears to result, at least in part, from activation of an alternative mRNA start site approximately 200 nucleotides upstream of the normal start site; this site is not used in unstressed or heat-stressed tissues. The effect of cadmium on the RNA splicing of Bz2 seems to be specific: splicing of other introncontaining maize genes, including a maize actin gene under the control of the cadmium-inducible 822 promoter, is unaffected by cadmium stress. Conversely, 822 intron splicing is not affected by other stress conditions that induce Bz2 gene expression, such as abscisic acid, auxin, or cold stress. Surprisingly, the increase in Bz2 mRNA during cadmium stress does not result in an increase in Bz2 glutathione Stransferase activity. We propose that an alternative protein may be encoded by 822 that has a role during responses t o heavy metals.Specific enzymatic and regulatory roles have been assigned for most genes of the anthocyanin pathway in maize (Zea mays) as a result of genetic and biochemical analysis. Bz2 is one of the last structural genes required for the production of anthocyanin pigmentation in maize (Coe et al., 1988;Holton and Cornish, 1995). In bz2 mutants cytoplasmic synthesized anthocyanin precursors are unable to reach their final destination in the vacuole. This inappropriate cytoplasmic accumulation of the precursor pigment cyanidin-3-glucoside causes tissues to develop a bronze color as a result of oxidation and condensation reactions that are poorly understood (Stafford, 1990). These oxidized secondary metabolites in the cytoplasm of bz2 mutants are

Cloning and Sequencing of cDNAs for Hypothetical Genes from Chromosome 2 of Arabidopsis,

“…The alternative gene product, transposon-associated protein, has significant homology to the C terminus of the Mutator transposase (Comelli et al, 1999). The alternate unspliced, introncontaining transcript from the maize Bronze-2 locus was increased 50-fold by cadmium stress on maize seedlings and was proposed to have a role during response to heavy metals (Marrs and Walbot, 1997). However, the unspliced introns observed in cDNAs from At2g23050 and At2g44220 may be either alternative splicing products or may arise from immature nuclear transcripts present in the cDNA populations used for RACE.…”

Literature review: Phytoaccumulation of chromium, uranium, and plutonium in plant systems

“…This mechanism has been confirmed by the use of vanadate, which inhibits transport into the vacuole by inhibiting the tonoplast GSH pump (Marrs et al 1996). Both Bz2 and GmGST26-A belong to a group of type III GSTs, which are induced by a variety of environmental stresses, including heavy metals such as Cd (Marrs and Walbot, 1997). Cadmium induces a higher transcription rate of Bz2, and apparently two, not one, species of mRNA are produced.…”

“…For example, Cd, has been shown to induce the biosynthesis of both GSTs and PCS (Rauser and Meuwly, 1995). Marrs and Walbot (1997) hypothesize that the newly synthesized, truncated GST induced by Cd, fuses with the PC-heavymetal complex and shuttles it across the tonoplast and into the vacuole. In soybean GmGST26-A, a gene induced by Cd, also produces both the full length and the truncated GST proteins (Czarnecka et al 1988).…”

“…In addition to one mRNA species coding for GST, a second mRNA species codes for a new truncated GST protein which is missing the enzyme activity domain, but retains the dimerization and glutathione (GSH)-binding domains. Therefore, the end result is two proteins, one of which is the normal GST which targets the anthocyanin precursor to the vacuole, while the other appears to be involved in the heavy metal transport into and accumulation within the vacuole (Marrs and Walbot, 1997).…”

Using Wastewater as a Source of N in Agriculture: Emissions of Gases and Reuse of Sludge on Soil Fertility

“…As an alternative, in Italy, experiments have been performed with natural technologies for mud treatment, with the goal of reducing costs of investment and eliminating the practical maintenance costs of the system, through stabilization of muds by the process of phytomineralization and biological conditioning when preparing tecnosuoli for agricultural and environmental use . For example, with the use of Phragmites australis, a rhizomatose plant from the Poaceae family that has interesting characteristics for its use in phytoremediation or phytostabilization of nitrogen, phosphorous, organic compounds and heavy metals in water (Marrs and Walbot, 1997;Peruzzi et al, 2010).…”