OsRAM2 Function in Lipid Biosynthesis Is Required for Arbuscular Mycorrhizal Symbiosis in Rice
OsRAM2 Function in Lipid Biosynthesis Is Required for Arbuscular Mycorrhizal Symbiosis in Rice
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OsRAM2 在脂质生物合成中的功能是水稻丛枝菌根共生所必需的
DOI：
10.1094/mpmi-04-21-0097-r
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发表时间：
2022-03-01
影响因子：
3.5
通讯作者：
Wang, Bin
中科院分区：
文献类型：
--
作者：
Liu, Ying-Na;Liu, Cheng-Chen;Wang, Bin
丛枝菌根（AM）是一种由球囊霉亚门真菌与大多数陆生植物形成的互惠共生体。在共生过程中，植物为真菌提供有机碳，以换取矿物质营养。以往的豆科植物研究表明，所需的丛枝菌根2（RAM 2）基因是必要的脂质从植物转移到AM真菌（AMF），也可能发挥信号作用，在根表面。为了进一步研究RAM 2在其他植物谱系中的功能，本研究鉴定了两个水稻（Oryza sativa）基因OsRAM 2和OsRAM 2L为豆科植物RAM 2的直向同源基因。在共生过程中检查它们的表达模式显示，只有OsRAM 2在AMF接种后强烈上调。然后进行CRISPR/Cas9诱变以获得三个Osram 2突变株系（-1、-2和-3）。接种AMF Rhizophagus irregularis或Funneliformis mosseae后，所有突变系均表现出极低的定殖率，并且很少观察到的丛枝都有缺陷，从而支持了RAM 2在单子叶植物和双子叶植物谱系之间保守的营养作用。至于信号作用，虽然两种AMF在Osram 2突变体上形成的菌丝足数量确实减少，但它们的形态没有显示出异常，真菌菌丝成功侵入根部。启动子活性进一步表明OsRAM 2不表达于菌丝足下方的表皮细胞或包围真菌菌丝的外皮层细胞中，而是仅表达于含有丛枝的皮层细胞中。因此，这表明RAM 2的间接作用，而不是直接参与确定在根表面的共生信号。
Arbuscular mycorrhiza (AM) is a mutualistic symbiosis formed between most land plants and Glomeromycotina fungi. During symbiosis, plants provide organic carbon to fungi in exchange for mineral nutrients. Previous legume studies showed that the required for arbuscular mycorrhization2 (RAM2) gene is necessary for transferring lipids from plants to AM fungi (AMF) and is also likely to play a signaling role at the root surface. To further explore RAM2 functions in other plant lineages, in this study, two rice (Oryza sativa) genes, OsRAM2 and OsRAM2L, were identified as orthologs of legume RAM2. Examining their expression patterns during symbiosis revealed that only OsRAM2 was strongly upregulated upon AMF inoculation. CRISPR/Cas9 mutagenesis was then performed to obtain three Osram2 mutant lines (-1,-2, and-3). After inoculation by AMF Rhizophagus irregularis or Funneliformis mosseae, all of the mutant lines showed extremely low colonization rates and the rarely observed arbuscules were all defective, thus supporting a conserved nutritional role of RAM2 between monocot and dicot lineages. As for the signaling role, although the hyphopodia numbers formed by both AMF on Osram2 mutants were indeed reduced, their morphology showed no abnormality, with fungal hyphae invading roots successfully. Promoter activities further indicated that OsRAM2 was not expressed in epidermal cells below hyphopodia or outer cortical cells enclosing fungal hyphae but instead expressed exclusively in cortical cells containing arbuscules. Therefore, this suggested an indirect role of RAM2 rather than a direct involvement in determining the symbiosis signals at the root surface.