A novel stress-inducible metallothionein-like gene from rice

Abstract

A novel rice genomic sequence encoding coding segments homologous to other metallothionein-like genes was isolated from Oryza sativa genomic library. This sequence, hereby designated as rgMT (rice genomic metallothionein-like gene), consists of two exons and one intron. From the coding sequence, it is predicted that rgMT encodes one protein of 74 amino acids. Differential expression of rgMT in rice plants was observed as mature transcripts were more abundant in roots than in leaves and sheaths. Under different stress conditions, such as excess heavy metals and heat shock, expression of rgMT was significantly elevated. This was especially noticeable with 250 microM CuCl2 for 16 h, 40 degrees C heat for 2 h and 0.06% DMSO for 1 h. Under sucrose starvation, rgMT transcripts also increased with time up to 72 h. During recovery from sucrose starvation, the transcripts declined slightly within 12 h of recovery. rgMT transcripts were also seen to have increased expression in senescent leaves. These results support the notion that rgMT is a stress-inducible gene in rice heretofore unreported.

Examining the Specific Contributions of Individual Arabidopsis Metallothioneins to Copper Distribution and Metal Tolerance

“…In angiosperms, MTs can be classified into four types based on the conserved positions of Cys residues (Cobbett and Goldsbrough, 2002). There are some general trends in the expression of these four types of MTs, with type-1 MTs expressed predominantly in roots, type-2 MTs in leaves, type-3 MTs in fruits, and type-4 MTs in seeds (Zhou and Goldsbrough, 1994;Hsieh et al, 1995;Zhou and Goldsbrough, 1995;Hsieh et al, 1996;Guo et al, 2003). We have previously shown that the genome of Arabidopsis contains seven genes encoding MTs (Cobbett and Goldsbrough, 2002).…”

“…Some evidence points to a role of plant MTs in Cu detoxification. In many plant species, including Arabidopsis, rice (Oryza sativa), and the metal hyperaccumulator Thlaspi caerulescens, MT gene expression is strongly induced by Cu treatment and, to a lesser degree, by Cd and Zn (Zhou and , 1994;Hsieh et al, 1995;Roosens et al, 2004). Expression of MT genes has also been shown to correlate closely with Cu tolerance among Arabidopsis ecotypes and between populations of Silene vulgaris and Silene paradoxa (Murphy and Taiz, 1995;van Hoof et al, 2001;Mengoni et al, 2003).…”

Mechanisms of stress avoidance and tolerance by plants used in phytoremediation of heavy metals

“…In plants they may participate in metal homeostasis since correlation between MT RNA levels and naturally occurring differences in tolerance to heavy metals in Arabidopsis ecotypes were observed (Murphy and Taiz 1995, Murphy et al 1997, Guo et al 2008. Other proposed functions of MTs in plants are: metal detoxifi cation (Domenech et al 2006, Roosens et al 2008, senescence (Coupe et al 1995, Hsieh et al 1995 and protection against abiotic stress (Zhou et al 2005). In different organisms, the MT expression correlates with metal concentration what suggests that they can be effective markers of environmental conditions (Morris et al 1999).…”

Molecular Characterization of Metallothionein Genes in Plants.

“…In the open reading frame, the type 1 MTs have one intron in pea (PsMTA) [26], rice (rgMT) [6] and maize (MT -L) [11], and two introns in cotton (MT1 -A) [31]; while the type 2 MTs have one intron in tomato (LeMTB) [32]. In the 5'-noncoding sequence of MT genes, a putative MRE (metal-responsive element) moiety was identified in pea [26] and tomato [32], but not in cotton [31].…”

“…Class I metallothioneins are the most puzzling and attractive group. Since the first full-length class I MT gene was reported in the flowering plant Mimulus guttatus [25], many more have been identified in a variety of plant species including pea [26], maize [11], soybean [27], Arabidopsis [13,15,28], Vicia faba [8], rape [5], kiwifruit [29], Sambucus nigra L. [4], wheat [10], rice [6,9,12,30], tobacco [7], cotton [31] and tomato [32]. More information on these class I MT genes is shown in Table 2.…”