School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India.
Department of Life Sciences, Sharda University, Greater Noida, UP, 201310, India.
Photosynth Res. 2023 Oct;158(1):57-76. doi: 10.1007/s11120-023-01041-x. Epub 2023 Aug 10.
The C4 plants photosynthesize better than C3 plants especially in arid environment. As an attempt to genetically convert C3 plant to C4, the cDNA of decarboxylating C4 type NADP-malic enzyme from Zea mays (ZmNADP-ME) that has lower Km for malate and NADP than its C3 isoforms, was overexpressed in Arabidopsis thaliana under the control of 35S promoter. Due to increased activity of NADP-ME in the transgenics the malate decarboxylation increased that resulted in loss of carbon skeletons needed for amino acid and protein synthesis. Consequently, amino acid and protein content of the transgenics declined. Therefore, the Chl content, photosynthetic efficiency (Fv/Fm), electron transport rate (ETR), the quantum yield of photosynthetic CO assimilation, rosette diameter, and biomass were lower in the transgenics. However, in salt stress (150 mM NaCl), the overexpressers had higher Chl, protein content, Fv/Fm, ETR, and biomass than the vector control. NADPH generated in the transgenics due to increased malate decarboxylation, contributed to augmented synthesis of proline, the osmoprotectant required to alleviate the reactive oxygen species-mediated membrane damage and oxidative stress. Consequently, the glutathione peroxidase activity increased and HO content decreased in the salt-stressed transgenics. The reduced membrane lipid peroxidation and lower malondialdehyde production resulted in better preservation, of thylakoid integrity and membrane architecture in the transgenics under saline environment. Our results clearly demonstrate that overexpression of C4 chloroplastic ZmNADP-ME in the C3 Arabidopsis thaliana, although decrease their photosynthetic efficiency, protects the transgenics from salinity stress.
C4 植物比 C3 植物光合作用更好，尤其在干旱环境中。为了尝试将 C3 植物基因转化为 C4 植物，我们在拟南芥中过表达了玉米的 NADP-苹果酸酶 C4 型脱羧酶（ZmNADP-ME）的 cDNA，其对苹果酸和 NADP 的 Km 值低于其 C3 同工型。该基因受 35S 启动子的控制。由于转基因中 NADP-ME 的活性增加，导致用于氨基酸和蛋白质合成的碳骨架损失，苹果酸脱羧作用增加。因此，转基因植物的氨基酸和蛋白质含量下降。因此，转基因植物的叶绿素含量、光合作用效率（Fv/Fm）、电子传递率（ETR）、光合 CO2 同化量子产率、莲座叶直径和生物量均较低。然而，在盐胁迫（150 mM NaCl）下，过表达植株的叶绿素、蛋白质含量、Fv/Fm、ETR 和生物量均高于载体对照。由于苹果酸脱羧作用增加，转基因植物中 NADPH 的产生有助于脯氨酸的合成增加，脯氨酸是缓解活性氧介导的膜损伤和氧化应激所需的渗透保护剂。因此，盐胁迫转基因植物中的谷胱甘肽过氧化物酶活性增加，HO 含量降低。膜脂质过氧化减少，丙二醛产量降低，导致盐胁迫下转基因植物类囊体完整性和膜结构更好地保存。我们的结果清楚地表明，尽管 C3 拟南芥中 C4 质体 ZmNADP-ME 的过表达降低了其光合作用效率，但它可以保护转基因植物免受盐胁迫。
