Abstract
Medicago ruthenica is a perennial forage legume with the remarkable ability to survive under unfavorable environmental conditions. It has been identified as an excellent species of Medicago that can adapt to various environmental stresses including low temperature, drought, and salinity. To investigate its potential as a genetic resource, we performed transcriptome sequencing and analysis in M. ruthenica under abiotic stresses. We generated >120 million reads from six cDNA libraries, resulting in 79,249 unique transcripts, most of which were highly similar to transcripts from M. truncatula (44,608, 56.3%) and alfalfa (M. sativa, 48,023, 60.6%). Based on gene expression profiles, 2,721 transcripts were identified as abiotic stress responsive genes which were predicted to be mainly involved in phytohormone signaling pathways, transcriptional regulation, and ROS-scavenging. These results suggest that they play critical roles in the response to abiotic stress. In summary, we identified genes in our transcriptome dataset involved in the regulation of the abiotic stress response in M. ruthenica which will provide a valuable resource for the future identification and functional analysis of candidate genes for adaption to unfavorable conditions. The genes identified here could be also useful for improving stress tolerance traits in alfalfa through molecular breeding in the future.
Highlights
In the natural environment, plant growth is often negatively affected by various unfavorable environmental conditions, such as temperature extremes, drought, and soil salinity
The seedlings were randomly divided into six groups: (1) for the control group, seedlings were grown at normal conditions as described above; (2) for the cold stress group, the seedlings were transferred to another chamber with the temperature set at 4 °C; (3) for the freezing group, the temperature was -8 °C; (4) for the osmotic stress group, the seedlings were treated with 300 mM mannitol solution; (5) for the salt stress group, the seedlings were treated with 200 mM NaCl solution; and (6) for the abscisic acid (ABA) treatment group, the seedling leaves were sprayed with 100 mM ABA solution
All DEGs were mapped to the M. truncatula transcript database for multi-species comparison, and the results showed that M. ruthenica and M. falcata are both important resources for the genetic improvement of alfalfa in response to abiotic stress (Figure S3)
Summary
Plant growth is often negatively affected by various unfavorable environmental conditions, such as temperature extremes, drought, and soil salinity. Unfavorable environments have selected for plants that can extensively modify their physiological and biochemical status to adapt to abiotic stresses, and these processes are controlled by complex regulatory networks involving numerous genes (Chinnusamy et al, 2004) Based on their roles in response to stress, the genes are classified into two major functional groups: the first group is mainly comprised of genes encoding osmoprotectants, heat shock proteins (HSP), late embryogenesis abundant proteins (LEA) (Cuevas-Velazquez et al, 2014), transporters (Dos Reis et al, 2012), antioxidants (such as peroxidase, superoxide dismutase, and glutathione peroxidase) (Gill and Tuteja, 2010) and various kinds of metabolism-related proteins. Numerous TFs, such as members of the AP2/ERF, MYB, and NAC families, have been identified and characterized as being important regulators in the abiotic stress response in model plants (Golldack et al, 2011; Chen et al, 2012; Mizoi et al, 2012)
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