Transgenic Alfalfa Plants Expressing the Sweetpotato Orange Gene Exhibit Enhanced Abiotic Stress Tolerance

Abstract

Alfalfa (Medicago sativa L.), a perennial forage crop with high nutritional content, is widely distributed in various environments worldwide. We recently demonstrated that the sweetpotato Orange gene (IbOr) is involved in increasing carotenoid accumulation and enhancing resistance to multiple abiotic stresses. In this study, in an effort to improve the nutritional quality and environmental stress tolerance of alfalfa, we transferred the IbOr gene into alfalfa (cv. Xinjiang Daye) under the control of an oxidative stress-inducible peroxidase (SWPA2) promoter through Agrobacterium tumefaciens-mediated transformation. Among the 11 transgenic alfalfa lines (referred to as SOR plants), three lines (SOR2, SOR3, and SOR8) selected based on their IbOr transcript levels were examined for their tolerance to methyl viologen (MV)-induced oxidative stress in a leaf disc assay. The SOR plants exhibited less damage in response to MV-mediated oxidative stress and salt stress than non-transgenic plants. The SOR plants also exhibited enhanced tolerance to drought stress, along with higher total carotenoid levels. The results suggest that SOR alfalfa plants would be useful as forage crops with improved nutritional value and increased tolerance to multiple abiotic stresses, which would enhance the development of sustainable agriculture on marginal lands.

Overexpression of Orange (OR) and OR mutant protein inChlamydomonas reinhardtiienhances carotenoid and ABA accumulation and increases resistance to abiotic stress

“…In our study, CrOR WT and CrOR His transgenic lines displayed an improved tolerance to salt and oxidative stresses (Figure 6 A, B and C), perhaps in part mediated by the overaccumulation of carotenoids in these lines. These results are consistent with the results previously reported in various plant species in which OR transgenes, especially plants overexpressing the mutated OR, were more tolerant against various abiotic stress conditions such as salt (Kim et al, 2013;Kim et al, 2019), paraquat (Goo et al, 2015, drought (Wang et al, 2015;Cho et al, 2016), and heat (Park et al, 2016;Kim et al, 2019). Additionally, Park et al…”

“…Overexpression of wild type OR resulted in high levels of carotenoids in various organs including sweetpotato storage roots, Arabidopsis leaves, rice grains, and corn endosperm (Park et al, 2015;Yuan et al, 2015a;Bai et al, 2016;Berman et al, 2017). Functional analysis of the OR genes in various orange-flesh melon fruits identified a single-nucleotide polymorphism known as 'golden SNP', which converts a highly-conserved arginine to histidine and is responsible for elevated β-carotene accumulation (Tzuri et al, 2015).…”

Selection of reliable reference genes for quantitative real-time RT-PCR in alfalfa

“…Alfalfa (Medicago sativa) is the largest forage crop worldwide (Wang et al, 2015). Considerable progress has been made to date by genetic and molecular studies on alfalfa, and high-throughput gene expression studies have become necessary for helping us to better understand and utilize this legume forage crop.…”

Molecular improvement of alfalfa for enhanced productivity and adaptability in a changing environment

“…To protect themselves, plants have developed a vast non‐enzymatic ROS‐scavenging network, including ascorbic acid and antioxidant secondary metabolites such as carotenoids and flavonoids. In line with this, the heterologous expression of the sweet potato ORANGE gene in a stress‐inducible manner in alfalfa resulted in increased carotenoid accumulation and enhanced tolerance to osmotic stress, such as salt and drought (Wang et al, ). In addition to these non‐enzymatic ROS‐scavenging mechanisms, various antioxidant enzymes are also utilized by plants to convert harmful free radicals into less toxic intermediates.…”