Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou, 310021, Zhejiang, China.
BMC Plant Biol. 2021 Nov 8;21(1):516. doi: 10.1186/s12870-021-03289-8.
Cucumber green mottle mosaic virus (CGMMV) causes substantial global losses in cucurbit crops, especially watermelon. N6-methyladenosine (mA) methylation in RNA is one of the most important post-transcriptional modification mechanisms in eukaryotes. It has been shown to have important regulatory functions in some model plants, but there has been no research regarding mA modifications in watermelon.
We measured the global mA level in resistant watermelon after CGMMV infection using a colorimetric method. And the results found that the global mA level significantly decreased in resistant watermelon after CGMMV infection. Specifically, mA libraries were constructed for the resistant watermelon leaves collected 48 h after CGMMV infection and the whole-genome mA-seq were carried out. Numerous mA modified peaks were identified from CGMMV-infected and control (uninfected) samples. The modification distributions and motifs of these mA peaks were highly conserved in watermelon transcripts but the modification was more abundant than in other reported crop plants. In early response to CGMMV infection, 422 differentially methylated genes (DMGs) were identified, most of which were hypomethylated, and probably associated with the increased expression of watermelon mA demethylase gene ClALKBH4B. Gene Ontology (GO) analysis indicated quite a few DMGs were involved in RNA biology and stress responsive pathways. Combined with RNA-seq analysis, there was generally a negative correlation between mA RNA methylation and transcript level in the watermelon transcriptome. Both the mA methylation and transcript levels of 59 modified genes significantly changed in response to CGMMV infection and some were involved in plant immunity.
Our study represents the first comprehensive characterization of mA patterns in the watermelon transcriptome and helps to clarify the roles and regulatory mechanisms of mA modification in watermelon in early responses to CGMMV.
黄瓜绿斑驳花叶病毒（CGMMV）可导致葫芦科作物，尤其是西瓜，遭受严重的全球损失。RNA 中的 N6-甲基腺苷（mA）甲基化是真核生物最重要的转录后修饰机制之一。它已被证明在一些模式植物中具有重要的调控功能，但在西瓜中尚未有关于 mA 修饰的研究。
我们使用比色法测量了 CGMMV 感染抗性西瓜后的全局 mA 水平。结果发现，CGMMV 感染后抗性西瓜中的全局 mA 水平显著降低。具体而言，构建了 CGMMV 感染后 48 小时抗性西瓜叶片的 mA 文库，并进行了全基因组 mA-seq。从 CGMMV 感染和对照（未感染）样本中鉴定出大量 mA 修饰峰。这些 mA 峰的修饰分布和基序在西瓜转录本中高度保守，但修饰程度高于其他已报道的作物植物。在对 CGMMV 感染的早期反应中，鉴定出 422 个差异甲基化基因（DMG），其中大多数为低甲基化，可能与西瓜 mA 去甲基化酶基因 ClALKBH4B 的表达增加有关。GO 分析表明，相当数量的 DMG 参与 RNA 生物学和应激响应途径。结合 RNA-seq 分析，西瓜转录组中 mA RNA 甲基化与转录水平之间通常呈负相关。在 CGMMV 感染后，59 个修饰基因的 mA 甲基化和转录水平均发生显著变化，其中一些基因参与植物免疫。
本研究首次全面描述了西瓜转录组中 mA 模式的特征，有助于阐明 mA 修饰在西瓜早期对 CGMMV 响应中的作用和调控机制。
