Co-transforming bar and CsALDH Genes Enhanced Resistance to Herbicide and Drought and Salt Stress in Transgenic Alfalfa (Medicago sativa L.)

Abstract

Drought and high salinity are two major abiotic factors that restrict the productivity of alfalfa. By application of the Agrobacterium-mediated transformation method, an oxidative responsive gene, CsALDH12A1, from the desert grass Cleistogenes songorica together with the bar gene associated with herbicide resistance, were co-transformed into alfalfa (Medicago sativa L.). From the all 90 transformants, 16 were positive as screened by spraying 1 mL L-1 10% Basta solution and molecularly diagnosis using PCR. Real-time PCR analysis indicated that drought and salt stress induced high CsALDH expression in the leaves of the transgenic plants. The CsALDH expression levels under drought (15 d) and salt stress (200 mM NaCl) were 6.11 and 6.87 times higher than in the control plants, respectively. In comparison to the WT plants, no abnormal phenotypes were observed among the transgenic plants, which showed significant enhancement of tolerance to 15 d of drought and 10 d of salinity treatment. Evaluation of the physiological and biochemical indices during drought and salt stress of the transgenic plants revealed relatively lower Na+ content and higher K+ content in the leaves relative to the WT plants, a reduction of toxic on effects and maintenance of osmotic adjustment. In addition, the transgenic plants could maintain a higher relative water content level, higher shoot biomass, fewer changes in the photosystem, decreased membrane injury, and a lower level of osmotic stress. These results indicate that the co-expression of the introduced bar and CsALDH genes enhanced the herbicide, drought and salt tolerance of alfalfa and therefore can potentially be used as a novel genetic resource for the future breeding programs to develop new cultivars.

Structural and Biochemical Characterization of Aldehyde Dehydrogenase 12, the Last Enzyme of Proline Catabolism in Plants

“…A recent study of transgenic alfalfa (Medicago sativa) expressing the ALDH12 gene from Cleistogenes songorica (CsALDH12) revealed that CsALDH12 upregulation resulted in increased salt and drought stress tolerance 50 . Additionally, these transgenic plants also showed an increased K + :Na + ratio and reduced malondialdehyde (a marker of oxidative stress) accumulation compared to wild-type plants, which are both signs of abiotic stress tolerance.…”

Genome-Wide Analysis of the Role of NAC Family in Flower Development and Abiotic Stress Responses in Cleistogenes songorica

“…C. songorica is known for its extreme stress tolerance and dimorphic floret [ 32 , 33 ]. Overexpression of the CsALDH gene improves salt and drought resistance in transgenic Arabidopsis thaliana and alfalfa [ 34 , 35 ]. There are two different types of flower of chasmogamous (CH) and cleistogamous (CL) in different positions of C. songorica .…”

Over-Expression of Arabidopsis EDT1 Gene Confers Drought Tolerance in Alfalfa (Medicago sativa L.)

“…Genes ectopically over-expressed in alfalfa can improve transgenic plant drought tolerance under laboratory conditions ( Zhang et al, 2005 , 2016 ; Jiang et al, 2009 ; Tang et al, 2013 ; Li et al, 2014 ; Duan et al, 2015 ; Wang et al, 2015 ). However, very few transgenic alfalfa plants have been tested in field trials ( Bao et al, 2016 ).…”

“…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 ). As a high-yielding and high-quality forage crop, alfalfa is extensively planted around the world.…”

“…In another study, a Cys2/His2-type zinc-finger protein gene GsZFP1 from Glycine soja was expressed in alfalfa: it improved drought resistance by enhancing the expression of several stress-responsive genes in alfalfa ( Tang et al, 2013 ). Besides TF genes, other genes such as the Orange gene from sweet potato, the CodA gene from bacteria, the NHX and VP1 genes from Zygophyllum xanthoxylum , and the ALDH and ZFP genes from Cleistogenes songorica have also been introduced into alfalfa in efforts to improve drought tolerance ( Bao et al, 2009 , 2016 ; Tang et al, 2013 ; Li et al, 2014 ; Duan et al, 2015 ; Wang et al, 2015 ; Zhang et al, 2016 ). Although the molecular mechanisms through which the ectopic expression of these various genes affect drought resistance may differ, each of them did improve drought resistance of transgenic alfalfa.…”