Down-Regulation of Metallothionein, a Reactive Oxygen Scavenger, by the Small GTPase OsRac1 in Rice

Wong, Hann Ling; Sakamoto, T.; Kawasaki, Tsutomu; Umemura, Kenji; Shimamoto, Ko

doi:10.1104/pp.103.036384

Cited by 300 publications

(246 citation statements)

References 64 publications

(90 reference statements)

Supporting

Mentioning

225

Contrasting

Unclassified

Order By: Relevance

“…In addition, the divergence of plant MT protein sequences and the complex expression patterns of MT genes suggest that the functions of MTs may not be limited to Cu detoxification. This is supported by studies showing that a type-2 MT in rice, OsMT2b, is involved in reactive oxygen species scavenging and signaling (Wong et al, 2004). In response to pathogen attack, this rice MT must be down-regulated to allow an oxidative burst that signals activation of host responses leading to disease resistance.…”

mentioning

confidence: 80%

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

2008

View full text Add to dashboard Cite

Metallothioneins (MTs) are small cysteine-rich proteins found in various eukaryotes. Plant MTs are classified into four types based on the arrangement of cysteine residues. To determine whether all four types of plant MTs function as metal chelators, six Arabidopsis (Arabidopsis thaliana) MTs (MT1a, MT2a, MT2b, MT3, MT4a, and MT4b) were expressed in the copper (Cu)-and zinc (Zn)-sensitive yeast mutants, Dcup1 and Dzrc1 Dcot1, respectively. All four types of Arabidopsis MTs provided similar levels of Cu tolerance and accumulation to the Dcup1 mutant. The type-4 MTs (MT4a and MT4b) conferred greater Zn tolerance and higher accumulation of Zn than other MTs to the Dzrc1 Dcot1 mutant. To examine the functions of MTs in plants, we studied Arabidopsis plants that lack MT1a and MT2b, two MTs that are expressed in phloem. The lack of MT1a, but not MT2b, led to a 30% decrease in Cu accumulation in roots of plants exposed to 30 mM CuSO 4 . Ectopic expression of MT1a RNA in the mt1a-2 mt2b-1 mutant restored Cu accumulation in roots. The mt1a-2 mt2b-1 mutant had normal metal tolerance. However, when MT deficiency was combined with phytochelatin deficiency, growth of the mt1a-2 mt2b-1 cad1-3 triple mutant was more sensitive to Cu and cadmium compared to the cad1-3 mutant. Together these results provide direct evidence for functional contributions of MTs to plant metal homeostasis. MT1a, in particular, plays a role in Cu homeostasis in the roots under elevated Cu. Moreover, MTs and phytochelatins function cooperatively to protect plants from Cu and cadmium toxicity.Metal ions, including those of iron, zinc (Zn), and copper (Cu), are required for catalytic and structural properties of many proteins and are therefore essential for growth and development of all organisms. However, excessive amounts of these metals, or of nonessential metals such as cadmium (Cd) and lead, are toxic and inhibit plant growth. To maintain proper metal homeostasis, organisms are equipped with a repertoire of mechanisms to regulate the uptake and distribution of specific metal ions. Nonessential metals and excessive amounts of essential metals can be detoxified by a variety of mechanisms including secretion, compartmentalization, or chelation by metal ligands (Hall, 2002

show abstract

mentioning

confidence: 80%

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

2008

View full text Add to dashboard Cite

show abstract

“…Although Os Rac1 is a positive regulator of defense in rice (Kawasaki et al, 1999;Ono et al, 2001;Suharsono et al, 2002;Wong et al, 2004), Hv RacB in barley (Schultheiss et al, 2002) and Nt Rac5 in tobacco (Morel et al, 2004) are negative regulators of defense response. In this study, the yeast two-hybrid assay showed that all Os Rac proteins, except for Os Rac4, interact with more than one Rboh proteins.…”

Section: Discussionmentioning

confidence: 99%

“…The polybasic C-terminal region of Os Rac1 efficiently targeted the chimeric protein to the plasma membrane in the rice protoplast ( Figure 4B). The core construct was fused with a maize (Zea mays) ubiquitin promoter, which has been shown to be highly active in rice cells (Wong et al, 2004).…”

Section: Fret Analysis Of Os Rac1-rbohb Interaction In Rice Protoplastsmentioning

confidence: 99%

Regulation of Rice NADPH Oxidase by Binding of Rac GTPase to Its N-Terminal Extension

et al. 2007

Self Cite

View full text Add to dashboard Cite

Reactive oxygen species (ROS) produced by NADPH oxidase play critical roles in various cellular activities, including plant innate immunity response. In contrast with the large multiprotein NADPH oxidase complex of phagocytes, in plants, only the homologs of the catalytic subunit gp91 phox and the cytosolic regulator small GTPase Rac are found. Plant homologs of the gp91 phox subunit are known as Rboh (for respiratory burst oxidase homolog). Although numerous Rboh have been isolated in plants, the regulation of enzymatic activity remains unknown. All rboh genes identified to date possess a conserved N-terminal extension that contains two Ca 2þ binding EF-hand motifs. Previously, we ascertained that a small GTPase Rac (Os Rac1) enhanced pathogen-associated molecular pattern-induced ROS production and resistance to pathogens in rice (Oryza sativa). In this study, using yeast two-hybrid assay, we found that interaction between Rac GTPases and the N-terminal extension is ubiquitous and that a substantial part of the N-terminal region of Rboh, including the two EF-hand motifs, is required for the interaction. The direct Rac-Rboh interaction was supported by further studies using in vitro pulldown assay, a nuclear magnetic resonance titration experiment, and in vivo fluorescence resonance energy transfer (FRET) microscopy. The FRET analysis also suggests that cytosolic Ca 2þ concentration may regulate Rac-Rboh interaction in a dynamic manner. Furthermore, transient coexpression of Os Rac1 and rbohB enhanced ROS production in Nicotiana benthamiana, suggesting that direct Rac-Rboh interaction may activate NADPH oxidase activity in plants. Taken together, the results suggest that cytosolic Ca 2þ concentration may modulate NADPH oxidase activity by regulating the interaction between Rac GTPase and Rboh.

show abstract

“…Second, we did not include rice genes for which only negative effects on disease resistance were reported in rice. This is for example the case of the over-expression of the OsMT2b gene that confers enhanced susceptibility to blast (Wong et al 2004). Finally, there were genes that had only been tested in rice cell cultures but not in entire rice plants.…”

Section: Cell Deathmentioning

confidence: 99%

Potential Candidate Genes for Improving Rice Disease Resistance

Delteil

Zhang²,

Lessard³

et al. 2010

Rice

View full text Add to dashboard Cite

Diseases caused by fungal and bacterial pathogens like Magnaporthe oryzae and Xanthomonas oryzae pv. oryzae are responsible for considerable yield loss. Up to now, in rice, the modification of the expression of more than 60 genes from diverse origins has shown beneficial effects with respect to disease resistance. In this paper, we review this large set of data to identify the best genes and strategies to achieve disease resistance by transgenic approaches. Altered expression of genes involved in signal transduction and transcription may lead to many unwanted side effects, like lesion mimic phenotypes. Moreover, modification of resistance to abiotic stress has been neglected and should be carefully examined in the future. Genes like resistance genes and pathogenesis-related genes can confer broad spectrum and high levels of resistance to several pathogens. Preformed expression of defense is often observed but does not necessarily lead to detrimental effects. Although examples of gene pyramiding are scarce, they suggest that this is a very promising strategy. More field evaluation of the transgenic plants is required to draw final conclusions on the usefulness of these genes for improving disease resistance.

show abstract

Down-Regulation of Metallothionein, a Reactive Oxygen Scavenger, by the Small GTPase OsRac1 in Rice

Cited by 300 publications

References 64 publications

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

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

Regulation of Rice NADPH Oxidase by Binding of Rac GTPase to Its N-Terminal Extension

Potential Candidate Genes for Improving Rice Disease Resistance

Contact Info

Product

Resources

About