甜高粱吸收重金属镉的分子机理

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镉污染问题严重威胁着粮食安全和人类健康，如何有效治理土壤镉污染越来越受到人们的关注。作为最具前景的生物质能源植物之一，甜高粱具有茎秆含糖量高、生长周期短、生物量大、抗逆性强、适种范围广等优势，利用其修复镉污染土壤，茎秆和籽粒生产燃料乙醇，酒糟用于燃烧发电，镉元素可从灰烬中加以回收。这样镉就从食物链转移到能源链中，兼顾了生态和经济效益。但是，目前人们对甜高粱吸收镉的研究较少，且多局限于生理层面。同时，甜高粱作为一种非超富集植物，吸收的镉多储存于根中，限制了其从污染土壤中提取镉的能力。因此，解析甜高粱吸收镉的生理和分子机理、促进镉从根向地上部分的转运是提高甜高粱吸收镉能力的重要前提。

中国科学院植物研究所李银心研究组对来自全球不同地区的96个甜高粱品系进行了筛选，发现不同品系对镉的耐受、吸收和转运能力具有很大差异，并对镉转运能力强和弱的两个甜高粱品系H18和L69（镉转运系数相差4倍）进行了进一步研究。相关研究结果以“Comparative transcriptome combined with morpho-physiological analyses revealed key factors for differential cadmium accumulation in two contrasting sweet sorghum genotypes”为题发表在Plant Biotechnology Journal。

研究结果表明，H18通过共质体途径吸收的镉显著高于L69，且其根的内皮层中质外体屏障较L69更弱，木质部汁液中镉的含量也更高。研究人员利用比较转录组学，通过分析两个品系间的差异表达基因及镉响应基因的异同，将镉转运能力差异主要聚焦到苯丙素和木质素合成以及细胞壁修饰过程。同时，一些金属转运蛋白基因的差异表达也可能是导致两个甜高粱品系对镉吸收和转运能力不同的重要原因。由此，研究人员提出根的吸收、细胞壁的结合、内皮层的阻隔作用以及木质部装载等多个过程的协同作用决定了甜高粱对镉的吸收和转运能力。该研究从生理、细胞和分子水平初步揭示了甜高粱吸收镉的机理，鉴定出多个影响镉吸收和转运的关键基因，为利用生物技术提高甜高粱吸收镉的能力提供了新的靶标和思路。

图：影响甜高粱吸收镉的关键因子

李银心研究组助理研究员冯娟娟和博士研究生贾伟涛为论文的共同第一作者，李银心研究员为论文的通讯作者。该研究得到了国家重点研发项目和国家科技惠民计划的资助。

Abstract

Cadmium (Cd) is a widespread soil contaminant threatening human health. As an ideal energy plant, sweet sorghum (Sorghum bicolor (L.) Moench) has great potential in phytoremediation of Cd-polluted soils, although the molecular mechanisms are largely unknown. In this study, key factors responsible for differential Cd accumulation between two contrasting sweet sorghum genotypes (high-Cd accumulation one H18, and low-Cd accumulation one L69) were investigated. H18 exhibited a much higher ability of Cd uptake and translocation than L69. Furthermore, Cd uptake through symplasmic pathway and Cd concentrations in xylem sap were both higher in H18 than those in L69. Root anatomy observation found the endodermal apoplasmic barriers were much stronger in L69, which may restrict the Cd loading into xylem. The molecular mechanisms underlying these morpho-physiological traits were further dissected by comparative transcriptome analysis. Many genes involved in cell wall modification and heavy metal transport were found to be Cd-responsive DEGs and/or DEGs between these two genotypes. KEGG pathway analysis found phenylpropanoid biosynthesis pathway was over-represented, indicating this pathway may play important roles in differential Cd accumulation between two genotypes. Based on these results, a schematic representation of main processes involved in differential Cd uptake and translocation in H18 and L69 is proposed, which suggests that higher Cd accumulation in H18 depends on a multilevel coordination of efficient Cd uptake and transport, including efficient root uptake and xylem loading, less root cell wall binding, and weaker endodermal apoplasmic barriers.

说明：本文根据植物所官网报道整理而成。原文链接如下：

http://www.ibcas.ac.cn/keyanjinzhan/201709/t20170918_4861069.html

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