College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi Province, China.
BMC Plant Biol. 2020 Nov 12;20(1):516. doi: 10.1186/s12870-020-02673-0.
Crown gall disease, caused by the pathogenic bacterium Agrobacterium tumefaciens, is responsible for extensive economic losses in orchards. Cherry rootstock 'CDR-1' (Prunus mahaleb) shows high resistance but the mechanism remains unclear. Here, we examined the morphology of pathogen-infected root neck surface, determined the activity of 10 defense-related enzymes and the content of salicylic acid (SA) and jasmonic acid (JA), and also applied transcriptome analysis, transient expression and transgenic verification to explore the crown gall resistance genes in 'CDR-1' plants.
In our study, peroxidase increased in the first 10 days, while phenylalanine ammonialyase and lipoxygenase increased in the first 15 days post-infection. Four key enzymes in the AsA-GSH cycle also responded, to a certain extent; although JA content increased significantly after the treatment, the SA content did not. In a follow-up transcriptome analysis, the differentially expressed genes Pm4CL2, PmCYP450, PmHCT1, PmHCT2, and PmCAD were up-regulated. Based on the above results, we focused on the lignin biosynthetic pathway, and further measured lignin content, and found it increased significantly. The Pm4CL2 gene was used to conduct transient expression and transgenic experiments to verify its function in crown gall disease resistance. It showed the relative expression of the treatment group was almost 14-fold that of the control group at 12 h post-treatment. After the infection treatment, clear signs of resistance were found in the transgenic lines; this indicated that under the higher expression level and earlier activation of Pm4CL2, plant resistance was enhanced.
The crown gall resistance of 'CDR-1' is likely related to the lignin biosynthetic pathway, in which Pm4CL2 functions crucially during the plant defense response to the pathogen A. tumefaciens. The results thus offer novel insights into the defense responses and resistance mechanism of cherry rootstock 'CDR-1' against crown gall disease.
由病原菌根癌农杆菌引起的冠瘿病会给果园造成巨大的经济损失。樱桃砧木‘CDR-1’（李属欧洲甜樱桃）表现出高度抗性，但机制尚不清楚。本研究通过观察病原侵染根颈表面的形态，测定 10 种防御相关酶的活性及水杨酸（SA）和茉莉酸（JA）的含量，同时应用转录组分析、瞬时表达和转基因验证来探讨‘CDR-1’植株中冠瘿病抗性基因。
研究发现，过氧化物酶在感染后 10 天内增加，而苯丙氨酸解氨酶和脂氧合酶在感染后 15 天内增加。ASA-GSH 循环中的 4 种关键酶也有一定程度的响应；虽然 JA 含量在处理后显著增加，但 SA 含量没有增加。在随后的转录组分析中，上调了 Pm4CL2、PmCYP450、PmHCT1、PmHCT2 和 PmCAD 等差异表达基因。基于上述结果，我们重点关注木质素生物合成途径，并进一步测量木质素含量，发现其含量显著增加。利用 Pm4CL2 基因进行瞬时表达和转基因实验，验证其在冠瘿病抗性中的功能。结果显示，处理组在处理后 12 小时的相对表达量几乎是对照组的 14 倍。在感染处理后，转基因株系表现出明显的抗性迹象；这表明在 Pm4CL2 表达水平较高且更早激活的情况下，植物抗性增强。
‘CDR-1’的冠瘿病抗性可能与木质素生物合成途径有关，其中 Pm4CL2 在植物对根癌农杆菌的防御反应中起着关键作用。研究结果为樱桃砧木‘CDR-1’抵抗冠瘿病的防御反应和抗性机制提供了新的见解。
