Abstract
Alfalfa (Medicago sativa L.) is an important legume forage crop with great economic value. However, as the growth of alfalfa is seriously affected by an inadequate supply of water, drought is probably the major abiotic environmental factor that most severely affects alfalfa production worldwide. In an effort to enhance alfalfa drought tolerance, we transformed the Arabidopsis Enhanced Drought Tolerance 1 (AtEDT1) gene into alfalfa via Agrobacterium-mediated transformation. Compared with wild type plants, drought stress treatment resulted in higher survival rates and biomass, but reduced water loss rates in the transgenic plants. Furthermore, transgenic alfalfa plants had increased stomatal size, but reduced stomatal density, and these stomatal changes contributed greatly to reduced water loss from leaves. Importantly, transgenic alfalfa plants exhibited larger root systems with larger root lengths, root weight, and root diameters than wild type plants. The transgenic alfalfa plants had reduced membrane permeability and malondialdehyde content, but higher soluble sugar and proline content, higher superoxide dismutase activity, higher chlorophyll content, enhanced expression of drought-responsive genes, as compared with wild type plants. Notably, transgenic alfalfa plants grew better in a 2-year field trial and showed enhanced growth performance with increased biomass yield. All of our morphological, physiological, and molecular analyses demonstrated that the ectopic expression of AtEDT1 improved growth and enhanced drought tolerance in alfalfa. Our study provides alfalfa germplasm for use in forage improvement programs, and may help to increase alfalfa production in arid lands.
Highlights
Alfalfa (Medicago sativa L.) is a widely planted, perennial legume forage crop; its growth requires little or no nitrogen fertilizer, as alfalfa has the ability to fix nitrogen through symbiotic bacteria (Jiang et al, 2009; Duan et al, 2015)
To investigate the drought tolerance potential of AtEDT1 in alfalfa, the open reading frame of AtEDT1 was introduced into alfalfa via Agrobacterium-mediated transformation
RT-PCR and qRT-PCR analysis revealed that AtEDT1 was expressed at various levels, and eight lines with relatively high expression levels were selected for further analysis (Figure 1)
Summary
Alfalfa (Medicago sativa L.) is a widely planted, perennial legume forage crop; its growth requires little or no nitrogen fertilizer, as alfalfa has the ability to fix nitrogen through symbiotic bacteria (Jiang et al, 2009; Duan et al, 2015). The NAC type TFs MlNAC9 from Miscanthus, ZmNAC55 from maize, GhNAC2 from cotton, and OsNAC6 from rice enhanced drought tolerance when expressed in various other plant species (Gunapati et al, 2016; Mao et al, 2016; Zhao et al, 2016; Lee et al, 2017). The use of these TFs to improve quantitative traits like drought tolerance is ideal, because they can simultaneously regulate the expression of many genes involved in drought response
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