植物防御素调控水稻镉积累的新机制

doi:10.11983/CBB18056

摘要/Abstract

摘要： 镉是我国农产品的主要重金属污染物之一。随着我国土壤重金属污染问题日益突出, 包括稻米在内的农产品重金属超标时常发生。如何防控重金属在作物可食部位的积累, 在保证农产品安全的同时将农田重金属进行移除修复, 已成为我国农业生产急需解决的问题。最近, 中科院上海生命科学院植物生理生态所龚继明研究组和中国水稻所钱前研究组克隆到1个特异调控镉在水稻(Oryza sativa)叶片中积累的主效QTL基因CAL1。CAL1编码1个植物防御素类似蛋白, 通过与镉进行螯合, 将镉从维管束木质部薄壁细胞中分泌出来, 进入木质部参与长距离转运, 从而定向调控镉在水稻叶片等营养器官的积累而不影响籽粒镉的积累。该研究加深了人们对重金属镉在植物体内的转运和再分配机理的认识, 同时也为培育秸秆镉高积累而籽粒镉含量达标的“修复型”水稻品种提供有价值的新基因。研究成果具有重要的理论意义和应用价值。

关键词: 水稻, 镉, 植物修复, 植物防御素

Abstract: Cadmium (Cd) is a highly toxic heavy metal that threatens human health. Rice is one of food crops that can accumulate Cd in the grain to levels that are unsafe for human consumption. With increasing contamination of heavy metals in paddy soils in China, considerable proportions of rice grain produced in some areas of southern China exceed the 0.2 mg·kg^-1 Cd limit of the Chinese food standard, which causes widespread public concern. Molecular breeding of rice varieties that accumulate Cd in straw for removing Cd from paddy soil while producing safe grain is one of the strategies for phytoremediation of contaminated soils. Recently, Luo et al. identified a quantitative trait locus CAL1 in rice that specifically regulates the accumulation of Cd in leaves. CAL1 encodes a defensin-like protein that can chelate Cd in the cytosol and facilitates Cd secretion from xylem parenchyma cells into xylem vessels for long-distance transport. The chelation of Cd to CAL1 appears to prevent Cd from being loaded into the phloem for transport to rice grain. Thus, CAL1 does not affect the accumulation of Cd in rice grain. These findings shed light on understanding the molecular mechanism of Cd translocation and allocation in rice and provide a molecular tool to breed rice varieties that may be used to remove Cd from the soil without affecting grain Cd concentration.

Key words: rice, cadmium, phytoremediation, defensin protein

黄新元, 赵方杰. 植物防御素调控水稻镉积累的新机制. 植物学报, 2018, 53(4): 451-455.

Huang Xinyuan, Zhao Fangjie. A Defensin-like Protein Regulates Cadmium Accumulation in Rice. Chinese Bulletin of Botany, 2018, 53(4): 451-455.

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链接本文: https://www.chinbullbotany.com/CN/10.11983/CBB18056

https://www.chinbullbotany.com/CN/Y2018/V53/I4/451

图/表 1

图1 水稻根部吸收和转运镉的示意图镉离子在水稻根部通过OsNRAMP5吸收进入外皮层, 随后部分镉被OsHMA3转运到液泡中进行区隔化。OsNRAMP5同时负责将镉离子从皮层细胞转运到内皮层细胞。位于木质部薄壁细胞的CAL1蛋白与镉进行螯合后被分泌到胞外, 进入木质部导管向地上部进行长距离运输。CAL1蛋白也在外皮层细胞中表达, 可能也与镉进行螯合之后分泌到皮层细胞中。然而, 介导CAL1-Cd螯合物跨膜转运是通过转运蛋白还是囊泡运输尚不清楚。

Figure 1 Schematic diagram of the uptake and transport of Cd in rice rootsThe uptake of Cd into rice roots is mediated by OsNRAMP5, which is also responsible for the transport of Cd from cortex cells into endodermis. Part of Cd is then sequestered into vacuoles by OsHMA3. In xylem parenchyma cells, Cd is chelated with CAL1 in the cytosol and then is secreted into the xylem vessels for long-distance transport to shoots. CAL1 is also expressed in exodermis, where CAL1 is also able to chelate Cd and potentially facilitates the Cd secretion from exodermis into cortex cells. However, it is still not clear whether transporters or vesicular trafficking pathways are responsible for translocating the CAL1-Cd complex across the plasma membrane.

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