Nicotinamide adenine dinucleotide (NAD) plays a central role in redox metabolism in all domains of life. Additional roles in regulating posttranslational protein modifications and cell signaling implicate NAD as a potential integrator of central metabolism and programs regulating stress responses and development. Here we found that NAD negatively impacts stomatal development in cotyledons of Arabidopsis thaliana. Plants with reduced capacity for NAD⁺ transport from the cytosol into the mitochondria or the peroxisomes exhibited reduced numbers of stomatal lineage cells and reduced stomatal density. Cotyledons of plants with reduced NAD⁺ breakdown capacity and NAD⁺‐treated cotyledons also presented reduced stomatal number. Expression of stomatal lineage‐related genes was repressed in plants with reduced expression of NAD⁺ transporters as well as in plants treated with NAD⁺. Impaired NAD⁺ transport was further associated with an induction of abscisic acid (ABA)‐responsive genes. Inhibition of ABA synthesis rescued the stomatal phenotype in mutants deficient in intracellular NAD⁺ transport, whereas exogenous NAD⁺ feeding of aba‐2 and ost1 seedlings, impaired in ABA synthesis and ABA signaling, respectively, did not impact stomatal number, placing NAD upstream of ABA. Additionally, in vivo measurement of ABA dynamics in seedlings of an ABA‐specific optogenetic reporter − ABAleon2.1 − treated with NAD⁺ showed increases in ABA content suggesting that NAD⁺ impacts on stomatal development through ABA synthesis and signaling. Our results demonstrate that intracellular NAD⁺ homeostasis as set by synthesis, breakdown and transport is essential for normal stomatal development, and provide a link between central metabolism, hormone signaling and developmental plasticity.

中文翻译：

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细胞内NAD状态的变化以脱落酸依赖性方式影响气孔发育

烟酰胺腺嘌呤二核苷酸（NAD）在生活的所有领域中的氧化还原代谢中起着核心作用。在调节翻译后蛋白质修饰和细胞信号转导中的其他作用暗示NAD是中央代谢的潜在整合者以及调节应激反应和发育的程序。在这里我们发现NAD对拟南芥子叶的气孔发育有负面影响。NAD ⁺从胞质溶胶进入线粒体或过氧化物酶体的能力降低的植物，其气孔谱系细胞数量减少，气孔密度降低。NAD ⁺分解能力和NAD ⁺降低的植物子叶经处理的子叶也减少了气孔数量。在NAD ⁺转运蛋白表达降低的植物以及用NAD ⁺处理的植物中，气孔谱系相关基因的表达受到抑制。NAD ⁺转运受损还与诱导脱落酸（ABA）响应基因有关。抑制ABA合成可以挽救缺乏细胞内NAD ⁺转运的突变体的气孔表型，而分别影响ABA合成和ABA信号传导的外源NAD ⁺饲喂aba-2和ost1幼苗的气孔表型不会影响气孔数，将NAD置于气孔表型的上游。阿巴 此外，体内NAD ⁺处理的ABA特异性光遗传报告基因-ABAleon2.1-的幼苗中ABA动态的测量显示ABA含量增加，表明NAD ⁺通过ABA合成和信号传导影响气孔发育。我们的结果表明，通过合成，分解和转运确定的细胞内NAD ⁺动态平衡对于正常的气孔发育至关重要，并提供了中央代谢，激素信号传导和发育可塑性之间的联系。