棉花对土壤镉污染修复效应及镉胁迫下应答调控的分子基础

Cadmium (Cd), accumulated in soils as a consequence of agricultural activities (excessive phosphatic fertilizers application) and industrial activities (mining and smelting of metalliferous ores, electroplating, etc.) is becoming a major problem due to the great toxicity, high mobility from soil to plant, long half-life of Cd and further entry into food chain. It is therefore necessary to reduce the soil Cd level to ensure the safety of agricultural products and also ensure the sustainable and efficient use of the Cd contaminated soil. Phytoremediation of Cd polluted soils has attracted world-wide attention and research. The most effective way of reducing the Cd level in soil is to breed Cd tolerant cultivars which have no or less Cd in their edible parts. Cotton (Gossypium hirsutum L.) is one of the important fiber crops in the world, and it is also an ideal candidate crop to control the soil pollution. Thus it is imperative to screen and utilize the genetic resources of cotton in phytoremediation. In this study, we will explore the genetic features of the Cd tolerance in cotton seedlings and their tolerance characteristics by using the Cd-tolerant cotton cultivar namely D90, which selected from the Cd polluted fields, and focus on exploring the molecular mechanisms of cotton responses to Cd stresses and identifying some regulatory genes related to Cd-tolerance by analyzing the epigenetic variation, proteomic and transcriptomic profiling between the tolerant cultivars and control which is sensitive to Cadmium. It will provide valuable information for revealing the molecular mechanisms in Cd-tolerant cotton and shedding light on exploring the proper basis for breeding new cotton germplasm which have resistance to heavy metal stress. Moreover, it is great importance to propose strategies for controlling the Cd and other heavy metal pollution.

随着工业化进程的加深，重金属镉（Cd）污染日益严重，镉在土壤-植物系统的迁移行为已经成为学术界热切关注的议题。土壤镉修复成为保证农产品质量安全和持续高效的利用土地资源的一项重要科学任务。棉花作为一种重要的非食用性经济作物，主产品是棉纤维，是一种非常适合用于治理土壤镉污染的侯选作物。因此，耐镉棉花新品种选育与利用对于镉污染土壤的植物修复具有十分必要意义，而棉花镉胁迫应答调控机制的研究则为此提供了理论基础。本研究以前期从重金属污染环境中筛选到的耐镉陆地棉种质D90为材料，研究棉花耐镉性状的遗传基础和镉在棉花体内的转运和积累；同时，通过耐镉种质与对照之间的DNA甲基化等表观遗传学差异和蛋白质表达差异结合转录组分析，筛选棉花镉胁迫应答下的调控关键基因，明确陆地棉镉胁迫应答机制的调控机制，解析陆地棉在镉污染土壤中的植物修复功能，为耐镉及其它重金属棉花遗传育种提供理论依据和基因基础。

本研究重点围绕“耐镉棉花响应镉胁迫的调控机制”这一中心，以耐镉陆地棉种质D90为材料，设计杂交组合，明确了陆地棉耐镉性的遗传特性，针对相关生理性状，认为可根据母体的总体表现，利用杂种优势在处理中后期进行选择，并且以干重、POD活性和MDA含量作为衡量耐镉性的部分性状选育品种时，应在处理中后期进行效果较好，同时在选择时不仅要考虑亲本和组合，还要考虑环境因素；棉花基因组 DNA 甲基化分析研究表明：镉胁迫可能诱导棉花基因组整体甲基化水平的提高，推测可能是由于其引起过氧化损伤，产生大量甲基自由基，引发了 DNA链的断裂损伤，从而导致DNA中5-甲基胞嘧啶含量的升高；通过细胞超微结构观察和能谱分析，明确了镉对棉花组织细胞的影响及Cd2+在棉花组织器官内的存在方式和分布情况；以镉敏感棉花种质TM-1和耐镉种质D90根及叶片为材料，明确了棉花响应镉胁迫过程的转录组表达谱，对比两种棉花种质根部的基因表达，进一步明确了大多数与金属转运、细胞壁合成及修饰相关的基因在正常生长条件下其在D90中的表达水平要高于TM-1；以镉敏感棉花种质TM-1和耐镉种质D90 48h时间点的根为材料，利用iTRAQ技术初步解析其蛋白组水平上的变化，认为糖酵解途径是最有可能在棉花镉胁迫胁迫中特异调控的代谢途径；采用Solexa深度测序技术获得供试棉花根系小分子RNA的数据信息，确定了多个与镉胁迫密切关联的miRNA及其靶基因；D90种质系对不同类型镉污染土壤的修复研究进一步证明了D90对镉的强耐性和富集能力。本研究结果在生理及分子水平上基本明确了棉花响应镉胁迫的时间表达、组织表达及遗传表达特点及其与主要性状的相关性，为进一步深入开展陆地棉镉胁迫应答机制的研究积累了较好的基因基础，也为耐镉及其它重金属棉花遗传育种提供理论依据。