Plant chemicals to promote rhizoremediation of POP-contaminated brownfields

根际是植物根部周围的区域，在这里植物和微生物之间发生复杂的相互作用。与植物根系共生的细菌被称为促进植物生长的根瘤菌（PGPR）。这种联系对两种生物都非常有益。PGPR保护植物免受疾病侵害，并产生植物生长刺激物。作为回报，植物会分泌出对PGPR整体活性有益的化合物。分泌物中含有的化学物质可以作为信号，促进PGPR和其他物质的根定植过程，如类黄酮和萜烯，它们可能诱导分解代谢途径，参与土壤有机物的降解，包括持久性污染物（POPs），如多氯联苯（PCBs）。因此，根际修复是植物将污染物泵入根际并释放促进根际细菌生长和诱导其POP分解代谢途径的化学物质的过程。根际修复是修复棕地最合适的技术之一，因为它的成本比其他替代方法低50%至80%，并且需要最少的干预。本研究的目标是：1-鉴定植物根系分泌物中诱导根际细菌定植特性的成分，从而促进根际细菌在土壤中的着床和存活；2-鉴定诱导PCB降解根瘤菌降解PCB的渗出物成分。这些化学品将具有很高的商业价值，因为它们将为协助植物修复过程提供额外的工具。具体目标将是：1-筛选具有利用苯丙素和降解持久性有机污染物双重能力的十字花科植物或豆科植物的天然PGPR；2-鉴定植物分泌物中的化学物质[十字花科植物（拟南芥）和豆科植物（紫花苜蓿）]通过PGPRs诱导植物根系定植性状；3-评价植物根分泌物化学物质对根细菌多氯联苯降解基因表达的影响；评估目标2和目标3中确定的效应物在微观实验中的影响。

Rhizosphere is the zone surrounding plant roots where complex interactions take place between plants, and microorganisms. The bacteria living in association with plant roots are called plant growth promoting rhizobacteria (PGPR). This association is highly beneficial for both organisms. PGPR protect plants against diseases and they produce plant growth stimulators. In return, plants exude compounds that are beneficial for overall activities of PGPR. Exudates contain chemicals that act as signal to promote the root colonization process by PGPR and others such as flavonoids and terpenes that may induce catabolic pathways involved in the degradation of soil organics including persistent pollutants (POPs) such as polychlorinated biphenyls (PCBs). Therefore, rhizoremediation is a process in which plants pump contaminants to the rhizosphere and release chemicals that promote rhizobacterial growth and induce their POP catabolic pathways.  Rhizoremediaton is among the most suitable technology for remediating brownsfields since its cost is 50 to 80% lower than alternatives and it requires a minimum of intervention. The objectives of this proposal are 1- to identify plant root exudates components that induce root colonization traits of rhizobacteria, thus facilitating their implantation and survival in soil; 2- to identify exudates components that induce PCB degradation by PCB-degrading rhizobacteria. These chemicals will be of high commercial value as they should provide an additional tool to assist the phytoremediation processes. The specific objectives will be 1- to screen for natural PGPR from crucifers or legumes exhibiting the dual ability of utilizing phenylpropanoids and degrading POPs; 2- To identify chemicals from plant exudates [crucifers (Arabidopsis thaliana) and legumes (Medicago sativa, alfalfa plant)] that act as effector to induce plant root colonization traits by PGPRs; 3- to evaluate the effect of chemicals from plant root exudates on expression of rhizobacterial PCB degrading genes; 4- To assess the influence of the effectors identified in objective 2 and 3 in microcosm assays.