Over-expression of a γ-tocopherol methyltransferase gene in vitamin E pathway confers PEG-simulated drought tolerance in alfalfa

Abstract

Background: α-Tocopherol is one of the most important vitamin E components present in plant. α-Tocopherol is a potent antioxidant, which can deactivate photoproduced reactive oxygen species (ROS) and prevent lipids from oxidation when plants suffer drought stress. γ-Tocopherol methyltransferase (γ-TMT) catalyzes the formation of αtocopherol in the tocopherol biosynthetic pathway. Our previous studies showed that over-expression of γ-TMT gene can increase the accumulation of α-tocopherol in alfalfa (Medicago sativa). However, whether these transgenic plants confer increased drought tolerance and the underlying mechanism are still unknown. Results: In the present study, we further evaluate transgenic alfalfa lines, and found that over-expression of MsTMT led to an increase in α-tocopherol and total tocopherol level in the transgenic lines compared with the control plant. It was revealed that drought tolerance of the transgenic alfalfa was remarkably increased, with alleviated oxidative damage and accumulation of more osmolytic substances. The stomatal development in transgenic plants was significantly inhibited on both sides of leaves, which may be resulted from the repression of MsSPCHLESS (MsSPCH) gene. The reduced stomatal density of transgenic plants contributes to a lower stomatal conductance and higher water use efficiency (WUE). Moreover, both RNA-seq and qRT-PCR analyses indicate that regulatory mechanism of MsTMT in drought involved in both ABA-dependent and ABA-independent pathways. Conclusion: Our results suggest that MsTMT gene plays a positive role in regulating alfalfa response to PEGsimulated drought stress, which might involve complex mechanisms, including ROS scavenging system, stomatal development and multiple phytohormone signaling pathways. This study will broaden our view on the function of γ-TMT gene and provide new strategy for genetic engineering in alfalfa breeding.

Improving oxidative stress resilience in plants

“…Besides the water-soluble antioxidants GSH and AA, the membrane-associated tocopherols prevent also oxidative damage to membranes. High levels of tocopherol in transgenic alfalfa overexpressing c-tocopherol methyltransferase increased the drought performance, probably supported by a decrease in stomatal development and a subsequently improved water use efficiency (Ma et al, 2020). Furthermore, carotenoids, crucial pigments required for photosynthesis, undergo oxidation by 1 O 2 and peroxyl radicals and dissipate energy from excited chlorophyll, thereby alleviating the negative impact of ROS on the photosynthetic machinery and minimizing their production (Rodriguez-Concepcion et al, 2018).…”

Extensive Variation in Drought-Induced Gene Expression Changes Between Loblolly Pine Genotypes

“…For instance, the most DET between clones (MSTRG.63087.2, LFC = 21.426) encodes a dihydroflavonol 4-reductase enzyme, which promotes the synthesis of flavonoids (Nakabayashi et al, 2014) in response to abiotic stress, including drought (Wang et al, 2013). A second transcript, MSTRG.18884.1, encodes the enzyme γ-tocopherol methyltransferase responsible for converting γ-tocopherol into α-tocopherol, a Vitamin E family member involved in plant stress tolerance and the response to lower soil moisture availability (Munné-Bosch, 2005;Ma et al, 2020). The large superfamily of cytochrome P450 (CYP450) is implicated in a variety of biosynthesis and detoxification pathways associated with plant growth and response to abiotic stress (Jun et al, 2015).…”

Functional Differentiation of BnVTE4 Gene Homologous Copies in α-Tocopherol Biosynthesis Revealed by CRISPR/Cas9 Editing

“…Their strong antioxidant capacity can reduce lipid peroxy radicals to corresponding hydrogen peroxide to avoid lipid peroxidation of polyunsaturated fatty acids. The high antioxidative property exerts a protective role in multiple plant stress responses such as cold and drought stress ( Janeczko et al, 2018 ; Ma et al, 2020 ). Most importantly, this effect can also be extended to human health.…”