Abstract

Backgroundα-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 α-tocopherol 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.ResultsIn 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.ConclusionOur results suggest that MsTMT gene plays a positive role in regulating alfalfa response to PEG-simulated 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.

Highlights

  • IntroductionPlants are always exposed to a range of abiotic stresses such as drought, salt, adverse temperature and heavy metals

  • As sessile organism, plants are always exposed to a range of abiotic stresses such as drought, salt, adverse temperature and heavy metals

  • This study reveals that over-expression of γ-Tocopherol methyltransferase (TMT) could affect stomatal development and response to drought stress, which will be useful for engineering alfalfa with improved vitamin E content, water use efficiency (WUE) and drought tolerance

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Summary

Introduction

Plants are always exposed to a range of abiotic stresses such as drought, salt, adverse temperature and heavy metals. Among these stresses, drought is one of the greatest natural constraints to agricultural production, which can result in more than 10% decrease in crop production [1]. ROS are relatively reactive and potentially harmful to plants due to unspecific oxidation of proteins and membrane lipids To eliminate these damage, plants have evolved protective mechanisms to maintain delicate equilibrium between ROS production and scavenging [2, 4,5,6]

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