De Novo Transcriptional Analysis of Alfalfa in Response to Saline-Alkaline Stress.

Yi-Min An,Li-Li Song,Ying-Rui Liu,Yong-Jun Shu,Chang-Hong Guo

doi:10.3389/fpls.2016.00931

Abstract

Saline-alkaline stress, caused by high levels of harmful carbonate salts and high soil pH, is a major abiotic stress that affects crop productivity. Alfalfa is a widely cultivated perennial forage legume with some tolerance to biotic and abiotic stresses, especially to saline-alkaline stress. To elucidate the mechanism underlying plant saline-alkaline tolerance, we conducted transcriptome analysis of whole alfalfa seedlings treated with saline-alkaline solutions for 0 day (control), 1 day (short-term treatment), and 7 days (long-term treatment) using ion torrent sequencing technology. A transcriptome database dataset of 53,853 unigenes was generated, and 2,286 and 2,233 genes were differentially expressed in the short-term and long-term treatment, respectively. Gene ontology analysis revealed 14 highly enriched pathways and demonstrated the differential response of metabolic pathways between the short-term and long-term treatment. The expression levels of 109 and 96 transcription factors were significantly altered significantly after 1 day and 7 days of treatment, respectively. Specific responses of peroxidase, flavonoids, and the light pathway component indicated that the antioxidant capacity was one of the central mechanisms of saline-alkaline stress tolerance response in alfalfa. Among the 18 differentially expressed genes examined by real time PCR, the expression levels of eight genes, including inositol transporter, DNA binding protein, raffinose synthase, ferritin, aldo/keto reductase, glutathione S-transferase, xyloglucan endotrans glucosylase, and a NAC transcription factor, exhibited different patterns in response to saline and alkaline stress. The expression levels of the NAC transcription factor and glutathione S-transferase were altered significantly under saline stress and saline-alkaline stress; they were upregulated under saline-alkaline stress and downregulated under salt stress. Physiology assays showed an increased concentration of reactive oxygen species and malondialdehyde and a decreased content of chlorophyll, indicating that anti-oxidation and detoxification play an important role in response to saline-alkaline stress. Overall, the transcriptome analysis provided novel insights into the saline-alkaline stress tolerance response mechanisms in alfalfa.

Highlights

Abiotic stresses, including drought, salinity, and extreme temperatures, adversely affect crop production worldwide
Contigs from all samples were assembled into 53,853 unigenes that were used to generate a non-redundant unigene library for further analysis of the M. sativa transcriptome under saline-alkaline stress
Transcriptome analysis showed that the component of the reactive oxygen species (ROS) scavenging pathway was dramatically upregulated under saline-alkaline stress conditions

Summary

Introduction

Abiotic stresses, including drought, salinity, and extreme temperatures, adversely affect crop production worldwide. Soil salinity and alkalinity are among the major abiotic factors that limit crop yield. In the Songnen Plain, the main crop production area of Northeast China, approximately 3.78 million hectares of land are threatened by soil salinization and alkalization (Yang and Wang, 2015). Sodic soils with high pH and salt concentration restrict plant growth and limit agricultural production in this area. Numerous studies have focused on plant salt tolerance; information on the combined saline and alkaline stress (hereafter referred to as saline-alkaline stress) is still limited. High pH due to soil alkalization is a crucial and critical stress condition compared with salinity stress, because increased ion concentrations have more adverse effects on plant growth than soil salinization alone. Alkaline stress is a more diversified form of stress, and plant tolerance to alkalinity reflects a more complex tolerance mechanism (Peng et al, 2008)

Methods

Results

Conclusion