Two metallothionein genes highly expressed in rice nodes are involved in distribution of Zn to the grain

Lei, Gui Jie; Yamaji, Naoki; Feng, Jian

doi:10.1111/nph.16860

Cited by 32 publications

(14 citation statements)

References 54 publications

(88 reference statements)

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“…Little is known how Cd and metals are transported from the nodes into the phloem. For Zn, rice mutants with knocked out genes that encode metallothionein in node I decreased the Zn transport from the node to the grain ( Lei et al, 2020 ). These proteins with S donor ligands seem to bind Zn also in the companion cells that are directly connected to the phloem without a membrane that separates these cells from the phloem.…”

Section: Discussionmentioning

confidence: 99%

“…Binding of Cd to organic ligands may impact the transfer of metals through membranes ( Zhao et al, 2016 ). In a next step, Cd storage forms could be coupled with membrane transporters by comparing wild-type and mutant plants that lack or overexpress specific membrane transporters ( Cadiou et al, 2017 ; Pokharel et al, 2018 ; Lei et al, 2020 ; Moore et al, 2020 ; Wiggenhauser et al, 2021 ; Zhang et al, 2021 ).…”

Section: Implications and Outlookmentioning

confidence: 99%

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Changes of Cadmium Storage Forms and Isotope Ratios in Rice During Grain Filling

et al. 2021

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Rice poses a major source of the toxic contaminant cadmium (Cd) for humans. Here, we elucidated the role of Cd storage forms (i.e., the chemical Cd speciation) on the dynamics of Cd within rice. In a pot trial, we grew rice on a Cd-contaminated soil in upland conditions and sampled roots and shoots parts at flowering and maturity. Cd concentrations, isotope ratios, Cd speciation (X-ray absorption spectroscopy), and micronutrient concentrations were analyzed. During grain filling, Cd and preferentially light Cd isotopes were strongly retained in roots where the Cd storage form did not change (Cd bound to thiols, Cd–S = 100%). In the same period, no net change of Cd mass occurred in roots and shoots, and the shoots became enriched in heavy isotopes (Δ114/110Cdmaturity–flowering = 0.14 ± 0.04‰). These results are consistent with a sequestration of Cd in root vacuoles that includes strong binding of Cd to thiol containing ligands that favor light isotopes, with a small fraction of Cd strongly enriched in heavy isotopes being transferred to shoots during grain filling. The Cd speciation in the shoots changed from predominantly Cd–S (72%) to Cd bound to O ligands (Cd–O, 80%) during grain filling. Cd–O may represent Cd binding to organic acids in vacuoles and/or binding to cell walls in the apoplast. Despite this change of ligands, which was attributed to plant senescence, Cd was largely immobile in the shoots since only 0.77% of Cd in the shoots were transferred into the grains. Thus, both storage forms (Cd–S and Cd–O) contributed to the retention of Cd in the straw. Cd was mainly bound to S in nodes I and grains (Cd–S > 84%), and these organs were strongly enriched in heavy isotopes compared to straw (Δ114/110Cdgrains/nodes–straw = 0.66–0.72‰) and flag leaves (Δ114/110Cdgrains/nodes–flag leaves = 0.49–0.52‰). Hence, xylem to phloem transfer in the node favors heavy isotopes, and the Cd–S form may persist during the transfer of Cd from node to grain. This study highlights the importance of Cd storage forms during its journey to grain and potentially into the food chain.

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Section: Discussionmentioning

confidence: 99%

Section: Implications and Outlookmentioning

confidence: 99%

Changes of Cadmium Storage Forms and Isotope Ratios in Rice During Grain Filling

et al. 2021

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“…OsVIT1 and OsVIT2 are expressed primarily in flag leaves and, as such, loss-of-function osvit1 and osvit2 mutants show increased Fe and Zn concentrations in seeds, and reduced accumulation in source flag leaves due to impaired vacuolar storage in the leaf blade (Zhang et al, 2012). In rice, MTs OsMT2b and OsMT2c are expressed in the phloem of enlarged vascular bundles of nodes, and play an important role in Zn distribution to grains through Zn chelation and transport in the phloem (Lei et al, 2021). osmt2b and osmt2c knockout mutants show increased accumulation of Zn in nodes and reduced Zn in the panicle, and subsequently impacted grain yield (Lei et al, 2021).…”

Section: Zn Accumulation In Seeds and Grainsmentioning

confidence: 99%

“…In rice, MTs OsMT2b and OsMT2c are expressed in the phloem of enlarged vascular bundles of nodes, and play an important role in Zn distribution to grains through Zn chelation and transport in the phloem (Lei et al, 2021). osmt2b and osmt2c knockout mutants show increased accumulation of Zn in nodes and reduced Zn in the panicle, and subsequently impacted grain yield (Lei et al, 2021). More detailed information on the transport of Zn within seeds can be found in Olsen and Palmgren (2014).…”

Section: Zn Accumulation In Seeds and Grainsmentioning

confidence: 99%

Zinc in plants: Integrating homeostasis and biofortification

et al. 2022

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Zinc plays many essential roles in life. As a strong Lewis acid that lacks redox activity under environmental and cellular conditions, the Zn 2+ cation is central in determining protein structure and catalytic function of nearly 10% of most eukaryotic proteomes. While specific functions of zinc have been elucidated at a molecular level in a number of plant proteins, wider issues abound with respect to the acquisition and distribution of zinc by plants. An important challenge is to understand how plants balance between Zn supply in soil and their own nutritional requirement for zinc, particularly where edaphic factors lead to a lack of bioavailable zinc or, conversely, an excess of zinc that bears a major risk of phytotoxicity. Plants are the ultimate source of zinc in the human diet, and human Zn deficiency accounts for over 400 000 deaths annually. Here, we review the current understanding of zinc homeostasis in plants from the molecular and physiological perspectives. We provide an overview of approaches pursued so far in Zn biofortification of crops. Finally, we outline a ''push-pull'' model of zinc nutrition in plants as a simplifying concept. In summary, this review discusses avenues that can potentially deliver wider benefits for both plant and human Zn nutrition.

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“…In a recent study, OsZIP4 was found to transport Zn to the phloem of diffuse vascular bundles in the node, leading to the efficient distribution of Zn to tiller buds and other developing tissues (Mu et al 2020 ). Additionally, two metallothionein genes, OsMT2b and OsMT2c , which are highly expressed in node I in rice, were demonstrated to distribute Zn to grains through chelation (Lei et al 2021 ). These molecular studies uncovered the mechanism of Zn distribution in rice and will enable the fine tuning of the efficient distribution of Zn in the edible parts of many crops.…”

Section: Introductionmentioning

confidence: 99%

Role of qGZn9a in controlling grain zinc concentration in rice, Oryza sativa L.

et al. 2021

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Key message A candidate gene responsible for higher grain zinc accumulation in rice was identified, which was probably associated with a partial defect in anther dehiscence. Abstract Zinc (Zn) is an essential mineral element in many organisms. Zn deficiency in humans causes various health problems; therefore, an adequate dietary Zn intake is required daily. Rice, Oryza sativa , is one of the main crops cultivated in Asian countries, and one of the breeding scopes of rice is to increase the grain Zn levels. Previously, we found that an Australian wild rice strain, O. meridionalis W1627, exhibits higher grain Zn levels than cultivated rice, O. sativa Nipponbare, and identified responsible genomic loci. An increase in grain Zn levels caused by one of the loci, qGZn9a , is associated with fertility reduction, but how this negative effect on grain productivity is regulated remains unknown. In this study, we artificially trimmed spikelets on the flowering day and found that a reduction in number of seeds was associated with an increase in the grain Zn levels. We also found that a partial defect in anther dehiscence correlated with the increase in grain Zn levels in plants carrying the W1627 chromosomal segment at qGZn9a in a Nipponbare genetic background. Among eight candidate genes in the qGZn9a region, three were absent from the corresponding region of W1627; one of these, Os09g0384900 , encoding a DUF295 protein with an unknown function, was found to be specifically expressed in the developing anther, thereby suggesting that the gene may be involved in the regulation of anther dehiscence. As fertility and grain Zn levels are essential agronomic traits in rice, our results highlight the importance of balancing these two traits. Supplementary Information The online version contains supplementary material available at 10.1007/s00122-021-03873-4.

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Two metallothionein genes highly expressed in rice nodes are involved in distribution of Zn to the grain

Cited by 32 publications

References 54 publications

Changes of Cadmium Storage Forms and Isotope Ratios in Rice During Grain Filling

Changes of Cadmium Storage Forms and Isotope Ratios in Rice During Grain Filling

Zinc in plants: Integrating homeostasis and biofortification

Role of qGZn9a in controlling grain zinc concentration in rice, Oryza sativa L.

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