一个水稻ABC转运蛋白耐镉分子机制研究

Cadmium (Cd) is a highly toxic heavy metal for humans, plants and other animals. Excess Cd in soils influences plant growth and development, and debases the quality of agricultural products. It has been found that several ABC transporters from different species could enhance Cd tolerance, but none has been reported in rice. The rice ABC subfamily C genes have been edited respectively using the CRISPR/Cas9 system in our lab, and a mutant sensitive to Cd toxicity was screened. The Cd-sensitive phenotype is due to the deletion of an ABC transporter gene (temporarily designated as OsCdT172), which is also induced by Cd toxicity in the wild-type Nipponbare. These results suggest that OsCdT172 is involved in Cd tolerance in rice. Based on the previous studies, molecular and physiological approaches are to be employed to analyze the organ/tissue distribution and subcellular localization of OsCdT172, and the changes in Cd uptake, translocation and accumulation in oscdt172 and over-expressing lines. Furthermore, the Cd transport activity of OsCdT172 is also to be assayed in rice protoplasts and yeast. Our study could elucidate the Cd-tolerance mechanism mediated by OsCdT172 in rice, and provide new genes for the molecular breeding of Cd-tolerant cultivars.

镉（Cd）是对人和动植物具有极强毒性的重金属元素。土壤中过量镉影响植物生长发育，降低农产品品质。目前在多个物种都发现ABC转运蛋白具有耐镉毒的功能，然而目前还没有ABC转运蛋白参与水稻镉毒耐受的报道。本项目前期通过CRISPR/Cas9工具对水稻ABC转运蛋白C亚家族基因进行编辑，发现其中一个基因（暂命名OsCdT172）的缺失导致水稻对镉毒敏感，并且该基因受镉毒诱导表达，这就表明OsCdT172参与水稻的镉毒耐受。本项目拟在此基础上，综合运用生理学、分子生物学技术方法研究OsCdT172表达的器官、组织及亚细胞定位，它的缺失和超表达对水稻镉吸收、分配及累积的影响。同时在水稻原生质体和酵母中研究其镉转运功能。本项目的完成可以阐明OsCdT172在水稻耐镉毒生理过程中的分子机制，同时为耐镉作物品种培育提供优良基因资源。

镉是对生物具有极强毒性的重金属元素。土壤中过量的镉抑制植物生长发育，降低作物产量和品质。农产品中累积的镉可通过食物链进入人体，危害健康。目前在多个物种都发现ABC转运蛋白具有耐镉毒的功能，然而水稻中只有极少数ABC转运蛋白参与镉毒耐受的报道。本项目研究了一个C型ABC转运蛋白OsCdT172（文献中系统命名为OsABCC9）在水稻镉耐受性和积累中的功能。镉处理可迅速诱导OsCdT172在根中表达，并且其表达水平呈镉浓度依赖性。高浓度锌也可以诱导OsCdT172表达，但高浓度铝和镧不影响其表达。OsCdT172定位于液泡膜，镉毒条件下主要在根中柱表达。OsCdT172的表达可增强酵母对镉的耐受性，并增加细胞内镉含量，说明OsCdT172的功能可能在于将镉隔离在液泡中，而非排出细胞。通过CRISPR/Cas9基因编辑技术得到了OsCdT172敲除突变体oscdt172-1和oscdt172-2。与野生型相比，OsCdT172突变体对镉毒更敏感，说明OsCdT172的存在可以增强水稻对镉毒的耐受性。高镉（5或10 μM）条件下，oscdt172突变体的根、木质部汁液、地上部和籽粒中的镉含量显著高于野生型，说明OsCdT172的缺失增加了镉从根向地上部的转移以及在籽粒中的积累。另外，突变体根中锌和铜的含量也有所增加。总之，OsCdT172通过将镉或其复合物隔离在根细胞液泡中，以增强水稻对镉的耐受性及减少镉向地上部的转移。OsCdT172可作为一个潜在的新基因资源，用于培育耐镉水稻品种。