The Key Laboratory of National Forestry and Grassland Administration for Tropical Forestry Research, Research Institute of Tropical Forestry, Chinese Academy of Forestry, Longdong, Guangzhou, 510520, China.
BMC Plant Biol. 2022 Jun 14;22(1):291. doi: 10.1186/s12870-022-03672-z.
Nerium indicum Mill. is an ornamental plant that is found in parks, riversides, lakesides, and scenic areas in China and other parts of the world. Our recent survey indicated the prevalence of witches' broom disease (WBD) in Guangdong, China. To find out the possible defense strategies against WBD, we performed a MiSeq based ITS sequencing to identify the possible casual organism, then did a de novo transcriptome sequencing and metabolome profiling in the phloem and stem tip of N. indicum plants suffering from WBD compared to healthy ones.
The survey showed that Wengyuen county and Zengcheng district had the highest disease incidence rates. The most prevalent microbial species in the diseased tissues was Cophinforma mamane. The transcriptome sequencing resulted in the identification of 191,224 unigenes of which 142,396 could be annotated. There were 19,031 and 13,284 differentially expressed genes (DEGs) between diseased phloem (NOWP) and healthy phloem (NOHP), and diseased stem (NOWS) and healthy stem (NOHS), respectively. The DEGs were enriched in MAPK-signaling (plant), plant-pathogen interaction, plant-hormone signal transduction, phenylpropanoid and flavonoid biosynthesis, linoleic acid and α-linoleic acid metabolism pathways. Particularly, we found that N. indicum plants activated the phytohormone signaling, MAPK-signaling cascade, defense related proteins, and the biosynthesis of phenylpropanoids and flavonoids as defense responses to the pathogenic infection. The metabolome profiling identified 586 metabolites of which 386 and 324 metabolites were differentially accumulated in NOHP vs NOWP and NOHS and NOWS, respectively. The differential accumulation of metabolites related to phytohormone signaling, linoleic acid metabolism, phenylpropanoid and flavonoid biosynthesis, nicotinate and nicotinamide metabolism, and citrate cycle was observed, indicating the role of these pathways in defense responses against the pathogenic infection.
Our results showed that Guangdong province has a high incidence of WBD in most of the surveyed areas. C. mamane is suspected to be the causing pathogen of WBD in N. indicum. N. indicum initiated the MAPK-signaling cascade and phytohormone signaling, leading to the activation of pathogen-associated molecular patterns and hypersensitive response. Furthermore, N. indicum accumulated high concentrations of phenolic acids, coumarins and lignans, and flavonoids under WBD. These results provide scientific tools for the formulation of control strategies of WBD in N. indicum.
辣木（Nerium indicum Mill.）是一种观赏植物，在中国和世界其他地区的公园、河边、湖边和风景区都有发现。我们最近的调查表明，中国广东地区存在辣木丛枝病（WBD）。为了寻找防治 WBD 的可能策略，我们对 N. indicum 植物的韧皮部和茎尖进行了基于 MiSeq 的 ITS 测序以鉴定可能的致病生物，然后与健康植株进行了从头转录组测序和代谢组谱分析。
调查显示，翁源县和增城区的发病率最高。在患病组织中最常见的微生物物种是 Cophinforma mamane。转录组测序结果鉴定了 191224 个非冗余基因，其中 142396 个可以注释。患病韧皮部（NOWP）与健康韧皮部（NOHP）以及患病茎（NOWS）与健康茎（NOHS）之间分别有 19031 和 13284 个差异表达基因（DEGs）。DEGs 在 MAPK 信号（植物）、植物-病原体相互作用、植物激素信号转导、苯丙烷和黄酮类生物合成、亚油酸和α-亚麻酸代谢途径中富集。特别是，我们发现辣木植物激活了植物激素信号、MAPK 信号级联、防御相关蛋白以及苯丙烷和黄酮类化合物的生物合成，作为对病原感染的防御反应。代谢组谱分析鉴定出 586 种代谢物，其中 386 种和 324 种代谢物在 NOHP 与 NOWP 以及 NOHS 与 NOWS 之间差异积累。观察到与植物激素信号、亚麻酸代谢、苯丙烷和黄酮类生物合成、烟酸和烟酰胺代谢以及柠檬酸循环相关的代谢物的差异积累，表明这些途径在对病原感染的防御反应中起作用。
我们的结果表明，广东大部分调查地区的辣木丛枝病发病率较高。C. mamane 疑似是辣木丛枝病的致病病原体。辣木植物启动了 MAPK 信号级联和植物激素信号，导致病原体相关分子模式和过敏反应的激活。此外，辣木植物在 WBD 下积累了高浓度的酚酸、香豆素和木脂素以及类黄酮。这些结果为制定辣木丛枝病防治策略提供了科学工具。
