Abstract
Abiotic stresses are critical delimiters for the increased productivity and cultivation expansion of sweet potato (Ipomoea batatas), a root crop with worldwide importance. The increased production of glycine betaine (GB) improves plant tolerance to various abiotic stresses without strong phenotypic changes, providing a feasible approach to improve stable yield production under unfavorable conditions. The gene encoding betaine aldehyde dehydrogenase (BADH) is involved in the biosynthesis of GB in plants, and the accumulation of GB by the heterologous overexpression of BADH improves abiotic stress tolerance in plants. This study is to improve sweet potato, a GB accumulator, resistant to multiple abiotic stresses by promoted GB biosynthesis. A chloroplastic BADH gene from Spinacia oleracea (SoBADH) was introduced into the sweet potato cultivar Sushu-2 via Agrobacterium-mediated transformation. The overexpression of SoBADH in the transgenic sweet potato improved tolerance to various abiotic stresses, including salt, oxidative stress, and low temperature. The increased BADH activity and GB accumulation in the transgenic plant lines under normal and multiple environmental stresses resulted in increased protection against cell damage through the maintenance of cell membrane integrity, stronger photosynthetic activity, reduced reactive oxygen species (ROS) production, and induction or activation of ROS scavenging by the increased activity of free radical-scavenging enzymes. The increased proline accumulation and systemic upregulation of many ROS-scavenging genes in stress-treated transgenic plants also indicated that GB accumulation might stimulate the ROS-scavenging system and proline biosynthesis via an integrative mechanism. This study demonstrates that the enhancement of GB biosynthesis in sweet potato is an effective and feasible approach to improve its tolerance to multiple abiotic stresses without causing phenotypic defects. This strategy for trait improvement in sweet potato not only stabilizes yield production in normal soils in unpredictable climates but also provides a novel germplasm for sweet potato production on marginal lands.
Highlights
Sweet potato (Ipomoea batatas) is a major root crop that ranks seventh in annual production worldwide and is grown in more than 100 countries as a valuable source of food, animal feed, and industrial raw material [1,2,3]
Three singleintegrated SoBADH transgenic sweet potato lines OE1, OE2 and OE3 were verified in a Southern blot analysis by hybridizing EcoRI-digested genomic DNA samples with a SoBADH-specific probe, and no integration was detected in the WT plants (Figure S3A)
The betaine aldehyde dehydrogenase (BADH) activity and a glycine betaine (GB) content of 0.52 mmol g21 were detected in the WT leaves, indicating that sweet potato is a natural accumulator of GB
Summary
Sweet potato (Ipomoea batatas) is a major root crop that ranks seventh in annual production worldwide and is grown in more than 100 countries as a valuable source of food, animal feed, and industrial raw material [1,2,3]. Because of its tolerance to a wide range of agroecological conditions, high yield potential, ease of cultivation, effective vegetative propagation and high nutritive value, the sweet potato is suitable for growth on marginal lands [2]. A strategy for producing energy from non-grain biomass resources using marginal lands to minimize the potential impact of bioenergy production on food security was developed in China [4]. A recent survey revealed an area of 34 million hm of marginal land available for growing bioenergy crops in China and, potentially, 45 million metric tons of liquid biofuels may be produced if 60% of this area is utilized [5,6]. As one of the most promising bioenergy crops, the sweet potato plays an important role in the development of first-generation biofuels in China [7]. New sweet potato varieties with enhanced tolerance to multiple abotic stresses are desirable
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