Table_5_Genes Involved in Stress Response and Especially in Phytoalexin Biosynthesis Are Upregulated in Four Malus Genotypes in Response to Apple Replant Disease.xlsx

Apple replant disease (ARD) is a soil-borne disease, which is of particular importance for fruit tree nurseries and fruit growers. The disease manifests by a poor vegetative development, stunted growth, and reduced yield in terms of quantity and quality, if apple plants (usually rootstocks) are replanted several times at the same site. Genotype-specific differences in the reaction of apple plants to ARD are documented, but less is known about the genetic mechanisms behind this symptomatology. Recent transcriptome analyses resulted in a number of candidate genes possibly involved in the plant response. In the present study, the expression of 108 selected candidate genes was investigated in root and leaf tissue of four different apple genotypes grown in untreated ARD soil and ARD soil disinfected by γ-irradiation originating from two different sites in Germany. Thirty-nine out of the 108 candidate genes were differentially expressed in roots by taking a p-value of < 0.05 and a fold change of > 1.5 as cutoff. Sixteen genes were more than 4.5-fold upregulated in roots of plants grown in ARD soil. The four genes MNL2 (putative mannosidase); ALF5 (multi antimicrobial extrusion protein); UGT73B4 (uridine diphosphate (UDP)-glycosyltransferase 73B4), and ECHI (chitin-binding) were significantly upregulated in roots. These genes seem to be related to the host plant response to ARD, although they have never been described in this context before. Six of the highly upregulated genes belong to the phytoalexin biosynthesis pathway. Their genotype-specific gene expression pattern was consistent with the phytoalexin content measured in roots. The biphenyl synthase (BIS) genes were found to be useful as early biomarkers for ARD, because their expression pattern correlated well with the phenotypic reaction of the Malus genotypes investigated.

苹果重茬病（Apple Replant Disease, ARD）是一种土传病害，对果树苗圃与果品种植者而言尤为关键。若在同一地块重复栽种苹果植株（通常为砧木），则会引发该病害，表现为营养生长不良、植株矮化，以及产量与品质双降。已有研究证实苹果植株对ARD的响应存在基因型特异性差异，但该症状背后的遗传机制仍鲜为人知。近期转录组分析筛选出一批可能参与植株响应过程的候选基因。本研究针对来自德国两个不同地块的未处理ARD土壤与经γ射线辐照消毒的ARD土壤，对4种不同苹果基因型的根系与叶片组织中108个筛选出的候选基因的表达水平展开了检测。以p值<0.05、倍数变化>1.5作为筛选阈值，108个候选基因中有39个在根系中呈现差异表达。其中16个基因在ARD土壤种植植株的根系中上调表达倍数超过4.5倍。MNL2（推定甘露糖苷酶）、ALF5（多抗菌挤出蛋白）、UGT73B4（尿苷二磷酸（UDP）糖基转移酶73B4）以及ECHI（几丁质结合蛋白）这4个基因在根系中显著上调表达。尽管此前从未在该研究背景中被报道过，但上述基因似乎与寄主植株对ARD的响应密切相关。其中6个高上调表达的基因隶属于植保素生物合成通路，其基因型特异性表达模式与根系中测得的植保素含量相一致。联苯合酶（BIS）基因可作为ARD的早期生物标志物，因其表达模式与所研究的苹果属（Malus）基因型的表型响应高度相关。