根边缘细胞缓解土荆芥淋溶途径化感作用对苦荞麦代谢扰动的机制

Mechanism of root border cells alleviate metabolic disturbance of Fagopyrum tataricum by the allelopathy of eluvial pathway from Chenopodium ambrosioides

土荆芥(Chenopodium ambrosioides)可通过淋溶途径的化感作用抑制周围植物的种子萌发和幼苗生长,而根边缘细胞(Root border cells,RBCs)对此具有缓解效应。为探讨这一效应的分子机制,以苦荞麦(Fagopyrum tataricum)为研究对象,测定了在土荆芥水浸提液处理前及处理后,保留RBC组和移除RBC组根尖活性氧(ROS)、超氧阴离子(O_(2)^(-))和丙二醛(MDA)含量以及抗氧化酶[超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)]活性的差异。再利用转录组测序分析上述处理对其代谢通路的影响,并进行qRT-PCR验证。结果表明:土荆芥水浸提液处理后,苦荞麦根尖ROS、O_(2)^(-)和MDA的含量以及抗氧化酶(POD和CAT)活性明显提高,且RBC移除组升高更多。通路分析表明,土荆芥水浸提液处理后,移除和保留RBCs组的苯丙素合成、α-亚麻酸代谢、类黄酮合成和谷胱甘肽代谢通路都显著发生改变。其中,苯丙素合成通路以抑制为主,且移除RBCs后受到抑制的程度更低;α-亚麻酸代谢通路中的甾酯水解酶(steryl ester hydrolase,TGL4)和磷脂酶A1(phospholipase A1,DAD1)的表达量大幅上调,而在移除RBCs组则未见变化,TGL4和DAD1负责将磷脂酰胆碱催化形成α-亚麻酸,为抑制植物生长并提高抗性的茉莉酸(JA)提供丰富的底物。此外,与根部疏水性有关的角质、木栓质和蜡合成通路只在移除RBCs组显著改变。上述结果表明,根边缘细胞通过影响根尖抗逆物质合成(苯丙素通路)、抗氧化酶和非酶抗氧化系统(类黄酮和谷胱甘肽)和根部疏水性等方面,以及提高茉莉酸(JA)的表达,在生长和防御中寻找平衡,缓解土荆芥水溶性物质化感胁迫;土荆芥水溶性物质成分复杂,具体哪一种成分在其化感作用中扮演主效作用,尚待进一步研究确证。

Root border cells(RBCs)are a group of cells that exhibit distinct gene expression patterns.They are detached from the tips of plant roots and distributed into the soil environment.Similar to mammalian immunocytes,RBCs create barriers within plant roots,thereby playing a significant role in plant defense mechanisms.Chenopodium ambrosioides,an invasive plant,exerts a substantial impact on neighboring plants,altering their morphology,physiology,and gene expression.The aqueous extract of C.ambrosioides inhibits the germination of seeds and growth of seedlings in Fagopyrum tataricum,whereas the root border cells alleviate the adverse effects of allelochemical stress.To investigate the molecular mechanism underlying this mitigating effect,we examined the changes in the levels of reactive oxygen species(ROS),superoxide anion(O_(2)^(-)),and malondialdehyde(MDA),as well as the activity of antioxidant enzymes(Superoxide dismutase,SOD;Peroxidase,POD;Catalase,CAT),in the group with preserved root border cells and the group with removed root border cells,following treatment with aqueous extracts of C.ambrosioides.The results demonstrated that treatment with the aqueous extract of C.ambrosioides significantly increased the levels of the ROS,O_(2),MDA,and the activities of antioxidant enzymes(POD and CAT)in root tips of Fagopyrum tataricum.The RBC-removing group exhibited a higher increase compared to the RBC-preserving group.Pathway analysis revealed the notable alterations in phenylpropanoid synthesis,alpha-linolenic acid metabolism,flavonoid synthesis,and glutathione metabolism in both the RBC-preserving and RBC-removing groups following treatment with the aqueous extract of C.ambrosioides.Specifically,the phenylpropanoid synthesis pathway was primarily suppressed,with a less degree of inhibition observed after removing RBCs.The expression levels of steryl ester hydrolase(TGL4)and phospholipase A1(DAD1)in the alpha-linolenic acid metabolism pathway were significantly upregulated,while no changes were observed in the RBC-removing group.TGL4 and DAD1 were responsible for catalyzing the conversion of phospholipid choline into alpha-linolenic acid,which provided abundant substrates for inhibiting plant growth and enhancing resistance to jasmonic acid(JA).Moreover,the synthesis pathways associated with cutin,suberin,and wax,which contributed to root hydrophobicity,were significantly altered exclusively in the RBCremoving group.These findings suggest that root border cells strive to achieve a balance between growth and defense by influencing the synthesis of stress-resistant substances(phenylpropanoid pathway),antioxidant enzymes,and nonenzymatic antioxidant systems(flavonoids and glutathione),while also enhancing the expression of JA.This,in turn,helps mitigate the allelopathic stress caused by water-soluble substances of C.ambrosioides.Finally,the composition of the aqueous extracts was complex and the component plays a major role in the allelopathy is still to be confirmed by further research.