National Key Laboratory of Wheat and Maize Crops Science/Collaborative Innovation Center of Henan Grain Crops/College of Agronomy, Henan Agricultural University, Zhengzhou, China.
Plant Biotechnol J. 2020 Dec;18(12):2420-2435. doi: 10.1111/pbi.13416. Epub 2020 Jun 14.
Cytosolic malate dehydrogenase (MDH) is a key enzyme that regulates the interconversion between malate and oxaloacetate (OAA). However, its role in modulating storage compound accumulation in maize endosperm is largely unknown. Here, we characterized a novel naturally occurring maize mdh4-1 mutant, which produces small, opaque kernels and exhibits reduced starch but enhanced lysine content. Map-based cloning, functional complementation and allelism analyses identified ZmMdh4 as the causal gene. Enzymatic assays demonstrated that ZmMDH4 predominantly catalyses the conversion from OAA to malate. In comparison, the activity of the mutant enzyme, which lacks one glutamic acid (Glu), was completed abolished, demonstrating that the Glu residue was essential for ZmMDH4 function. Knocking down ZmMdh4 in vivo led to a substantial metabolic shift towards glycolysis and a dramatic disruption in the activity of the mitochondrial complex I, which was correlated with transcriptomic alterations. Taken together, these results demonstrate that ZmMdh4 regulates the balance between mitochondrial respiration and glycolysis, ATP production and endosperm development, through a yet unknown feedback regulatory mechanism in mitochondria.
细胞质苹果酸脱氢酶（MDH）是一种关键酶，可调节苹果酸和草酰乙酸（OAA）之间的相互转化。然而，其在调节玉米胚乳中储存化合物积累中的作用在很大程度上尚不清楚。在这里，我们对一个新型的自然发生的玉米 mdh4-1 突变体进行了描述，该突变体产生小而不透明的籽粒，淀粉含量降低，但赖氨酸含量增加。基于图谱的克隆、功能互补和等位基因分析鉴定出 ZmMdh4 是该基因的候选基因。酶活性分析表明，ZmMDH4 主要催化 OAA 向苹果酸的转化。相比之下，突变酶（缺少一个谷氨酸（Glu））的活性完全丧失，表明 Glu 残基对于 ZmMDH4 的功能至关重要。体内敲低 ZmMdh4 导致糖酵解的大量代谢转变和线粒体复合物 I 的活性严重破坏，这与转录组的改变相关。综上所述，这些结果表明，ZmMDh4 通过线粒体中未知的反馈调节机制，调节线粒体呼吸和糖酵解、ATP 产生和胚乳发育之间的平衡。
