Characterization of a Novel Rice Metallothionein Gene Promoter: Its Tissue Specificity and Heavy Metal Responsiveness

Abstract

The rice (Oryza sativa L.) metallothionein gene OsMT-I-4b has previously been identified as a type I MT gene. To elucidate the regulatory mechanism involved in its tissue specificity and abiotic induction, we isolated a 1 730 bp fragment of the OsMT-I-4b promoter region. Histochemical β-glucuronidase (GUS) staining indicated a precise spacial and temporal expression pattern in transgenic Arabidopsis. Higher GUS activity was detected in the roots and the buds of flower stigmas, and relatively lower GUS staining in the shoots was restricted to the trichomes and hydathodes of leaves. No activity was observed in the stems and seeds. Additionally, in the root of transgenic plants, the promoter activity was highly upregulated by various environmental signals, such as abscisic acid, drought, dark, and heavy metals including Cu 2+ , Zn 2+ , Pb 2+ and Al 3+ . Slight induction was observed in transgenic seedlings under salinity stress, or when treated with Co 2+ and Cd 2+ . Promoter analysis of 5 -deletions revealed that the region −583/−1 was sufficient to drive strong GUS expression in the roots but not in the shoots. Furthermore, deletion analysis indicated important promoter regions containing different metalresponsive cis-elements that were responsible for responding to different heavy metals. Collectively, these findings provided important insight into the transcriptional regulation mechanisms of the OsMT-I4b promoter, and the results also gave us some implications for the potential application of this promoter in plant genetic engineering.

Bean Metal-Responsive Element-Binding Transcription Factor Confers Cadmium Resistance in Tobacco

“…Similar to the MRE of animal MT genes, several plant MREs are responsible for heavy metal-induced expression of reporter gene (Lü et al, 2007;Qi et al, 2007a;Dong et al, 2010). This indicates that MRE is a highly conserved MRE among plants and animals.…”

“…Interestingly, MRE also exists in the promoter regions of many Cd-responsive plant genes, such as Pseudotsuga menziesii metallothionein-like gene (PmMT; Chatthai et al, 2004), rice (Oryza sativa) metallothionein gene (ricMT; Lü et al, 2007), rice class I-4b metallothionein gene (OsMT-I-4b; Dong et al, 2010), and bean (Phaseolus vulgaris) stress-related gene2 (PvSR2; Qi et al, 2007a). Moreover, in rice, many Cd-responsive miRNA-encoding genes contain MREs in their promoters (Ding et al, 2011), suggesting that MREs may also be involved in Cdinduced transcription of noncoding genes in plants.…”

“…A 137-bp ricMT promoter fragment containing a MRE is required for copperactivated expression of GUS in transgenic Arabidopsis seedlings (Lü et al, 2007). The OsMT-I-4b promoter contains four copies of MREs and can confer heavy metalinducible expression of GUS in Arabidopsis plants (Dong et al, 2010). Although no plant MRE-binding proteins have been identified yet, these evidences strongly suggest that there must be some transcription factors directly binding MREs in these plants.…”

Lead Tolerance and Accumulation in Hirschfeldia incana, a Mediterranean Brassicaceae from Metalliferous Mine Spoils

“…Yeast functional complementation assays revealed that the expression of MT1a , MT2a and MT3a genes in Arabidopsis could increase the tolerance of yeast mutants to Cu and Cd [39], [40], [41]. However, with regard to Pb, little is known about the relationship between the induction of plant MT genes and lead tolerance [42], [43], [44]. It is also the same for phytochelatin that were identified as heavy metal-binding peptides involved in the accumulation, detoxification and metabolism of metal ions (for review [18]).…”

OsWRKY42 Represses OsMT1d and Induces Reactive Oxygen Species and Leaf Senescence in Rice

“…(C) Selected promoter fragments of lëjqNÇ (top). ChIP analysis was performed of the lëjqNÇ promoter using chroma-heavy metals, such as Cu² + , Pb² + and Al³ + (Dong et al, 2010). It would be therefore interesting to determine whether the W box element at -729~-724, defined as the OsWRKY42 binding site in our present study and located in the interval of the important lëjqNÇ promoter region, can also participate in the regulatory response to heavy metals.…”