The GUS reporter-aided analysis of the promoter activities of a rice metallothionein gene reveals different regulatory regions responsible for tissue-specific and inducible expression in transgenic Arabidopsis

Abstract

To gain a better understanding of the regulatory mechanism of plant metallothionein (MT) genes, a chimeric expression unit consisting of the beta-glucuronidase (gusA) reporter gene under the control of a 1,324 bp fragment of the rice MT (ricMT) promoter was introduced into Arabidopsis via Agrobacterium tumefaciens. The strongest histochemical staining for GUS activity was observed in the cotyledons and hypocotyls of the transgenic seedlings and in the stigma, filaments and anthers of young and mature flowers, and especially in the wounded tissues of transgenic plants. In contrast, a relatively low level of reporter gene expression was seen in the young roots of transgenic seedlings and no GUS activity was detected in the stems, seeds and leaves, but GUS activity was observed in cotyledons and the first two true leaves. Promoter analysis of 5' deletions further identified several important regions responsible for organ-specific expression including roots, flowers and wound induction, light and ABA, Cu and Zn responses. These findings demonstrate that a 1,324 bp fragment of the rice MT promoter performs a complicated transcriptional regulation with clearly functional regions in a model plant, and provide an important insight into the transcriptional regulation mechanisms that operate the temporal- and spatial-specific expression and stress responses of the rice MT gene. These results suggest that the ricMT promoter and its functional regions are potentially useful in genetic engineering of plants to express the desired genes whose products are preferentially needed in roots, flowers and wound induction.

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.…”

“…In the context of a minimal Cauliflower mosaic virus 35S promoter, the 35-bp PvSR2 promoter fragment containing a MRE can activate the expression of the GUS reporter gene in a metal-inducible manner in tobacco (Nicotiana tabacum) protoplasts (Qi et al, 2007a). 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).…”

The oil palm metallothionein promoter contains a novel AGTTAGG motif conferring its fruit-specific expression and is inducible by abiotic factors

“…In silico analysis of several plant MT promoters revealed the presence of cis-acting regulatory elements that confer responsiveness to abiotic and biotic stresses, such as the ethylene-responsive elements (ERE) (Whitelaw et al 1995), the abscisic acid-responsive elements (ABRE) (Zhou and Goldsbrough 1995), the W-box involved in wounding response (Endo et al 2007), the E-box involved in defense signaling, and the MYB-binding sites involved in drought inducibility (Lü et al 2007). Tissue-specific elements such as the root-specific element (RSE) have been identified in MT promoters from pea (Fordham-Skelton et al 1997) and oil palm (Siti Nor Akmar et al 2002).…”

“…Tissue-specific elements such as the root-specific element (RSE) have been identified in MT promoters from pea (Fordham-Skelton et al 1997) and oil palm (Siti Nor Akmar et al 2002). A few reports described the occurrence of a metal-responsive element (MRE) in plant MT promoters including the pea PsMTA promoter (Fordham-Skelton et al 1997), the tomato LeMT B promoter (Whitelaw et al 1995), the Douglas Fir PmMT promoter (Chatthai et al 2004), and the rice ricMT promoter (Lü et al 2007). The fact that plant MT promoters are enriched with tissue-specific, stress-inducible and metal-responsive regulatory elements suggests the presence of a complex regulatory mechanism controlling the expression of MT genes.…”