• Rice (Oryza sativa) is the staple food for over half the world’s population. Drought stress imposes major constraints on rice yields. Intriguingly, labdane‐related diterpenoid (LRD) phytoalexins in maize (Zea mays) affect drought tolerance, as indicated by the increased susceptibility of an insertion mutant of the class II diterpene cyclase ZmCPS2/An2 that initiates such biosynthesis. Rice also produces LRD phytoalexins, utilizing OsCPS2 and OsCPS4 to initiate a complex metabolic network.
• For genetic studies of rice LRD biosynthesis the fast‐growing Kitaake cultivar was selected for targeted mutagenesis via CRISPR/Cas9, with an initial focus on OsCPS2 and OsCPS4. The resulting cps2 and cps4 knockout lines were further crossed to create a cps2x4 double mutant. Both CPSs also were overexpressed.
• Strikingly, all of the cv Kitaake cps mutants exhibit significantly increased susceptibility to drought, which was associated with reduced stomatal closure that was evident even under well‐watered conditions. However, CPS overexpression did not increase drought resistance, and cps mutants in other cultivars did not alter susceptibility to drought, although these also exhibited lesser effects on LRD production.
• The results suggest that LRDs may act as a regulatory switch that triggers stomatal closure in rice, which might reflect the role of these openings in microbial entry.

中文翻译：

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拉丹相关二萜类天然产物在水稻气孔关闭中的（条件性）作用

• 大米（Oryza sativa）是世界一半以上人口的主食。干旱胁迫对水稻产量造成重大限制。有趣的是，玉米 ( Zea mays )中的拉丹相关二萜 (LRD) 植物抗毒素会影响耐旱性，这可以从启动这种生物合成的 II 类二萜环化酶ZmCPS2/An2的插入突变体的敏感性增加中看出。水稻还产生 LRD 植物抗毒素，利用OsCPS2和OsCPS4启动复杂的代谢网络。
• 对于水稻 LRD 生物合成的遗传研究，选择快速生长的 Kitaake 品种通过 CRISPR/Cas9 进行靶向诱变，最初的重点是OsCPS2和OsCPS4。将得到的cps2和cps4敲除系进一步杂交以产生cps2x4双突变体。两种CPS也都过表达。
• 引人注目的是，所有的 cv Kitaake cps突变体都表现出对干旱的敏感性显着增加，这与气孔关闭减少有关，即使在水分充足的条件下也很明显。然而，CPS过表达并没有增加抗旱性，其他品种的cps突变体也没有改变对干旱的敏感性，尽管这些对 LRD 生产的影响也较小。
• 结果表明，LRDs 可能充当触发水稻气孔关闭的调节开关，这可能反映了这些开口在微生物进入中的作用。