• Rice (Oryza sativa) is a staple food crop and serves as a model cereal plant. It contains two biosynthetic gene clusters (BGCs) for the production of labdane-related diterpenoids (LRDs), which serve important roles in combating biotic and abiotic stress. While plant BGCs have been subject to genetic analyses, these analyses have been largely confined to the investigation of single genes.
• CRISPR/Cas9-mediated genome editing was used to precisely remove each of these BGCs, as well as simultaneously knock out both BGCs.
• Deletion of the BGC from chromosome 2 (c2BGC), which is associated with phytocassane biosynthesis, but not that from chromosome 4 (c4BGC), which is associated with momilactone biosynthesis, led to a lesion mimic phenotype. This phenotype is dependent on two closely related genes encoding cytochrome P450 (CYP) mono-oxygenases, CYP76M7 and CYP76M8, from the c2BGC. However, rather than being redundant, CYP76M7 has been associated with the production of phytocassanes, whereas CYP76M8 is associated with momilactone biosynthesis. Intriguingly, the lesion mimic phenotype is not present in a line with both BGCs deleted.
• These results reveal directional cross-cluster phytotoxicity, presumably arising from the accumulation of LRD intermediates dependent on the c4BGC in the absence of CYP76M7 and CYP76M8, further highlighting their interdependent evolution and the selective pressures driving BGC assembly.

中文翻译：

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剖析水稻中与拉丹相关的二萜生物合成基因簇揭示了定向交叉簇的植物毒性

• 水稻（Oryza sativa）是一种主食作物，是一种模式谷类植物。它包含两个生物合成基因簇 (BGC)，用于生产与拉丹相关的二萜 (LRD)，在对抗生物和非生物胁迫中发挥重要作用。虽然植物 BGC 已接受遗传分析，但这些分析主要局限于对单个基因的研究。
• CRISPR/Cas9 介导的基因组编辑用于精确去除这些 BGC，并同时敲除两个 BGC。
• 从与植物卡桑生物合成相关的染色体 2 (c2BGC) 中删除 BGC，而不是从与莫米内酯生物合成相关的染色体 4 (c4BGC) 中删除 BGC，导致病变模拟表型。这种表型依赖于来自 c2BGC 的编码细胞色素 P450 (CYP) 单加氧酶CYP76M7和CYP76M8的两个密切相关的基因。然而， CYP76M7不是多余的，而是与植物卡桑的生产有关，而CYP76M8与莫米内酯的生物合成有关。有趣的是，病变模拟表型不存在于删除两个 BGC 的行中。
• 这些结果揭示了定向跨簇植物毒性，可能是由于在没有CYP76M7和CYP76M8的情况下依赖于 c4BGC 的 LRD 中间体的积累，进一步突出了它们相互依赖的进化和驱动 BGC 组装的选择压力。