Transcriptome Analyses Reveal Candidate Genes Potentially Involved in Al Stress Response in Alfalfa.

Wenxian Liu,Conghui Xiong,Lichao Ma,Longfeng Yan,Yanrong Wang,Zhengshe Zhang,Zhipeng Liu,Yajie Liu

doi:10.3389/fpls.2017.00026

Abstract

Alfalfa is the most extensively cultivated forage legume, yet most alfalfa cultivars are not aluminum tolerant, and the molecular mechanisms underlying alfalfa responses to Al stress are largely unknown. In this study, we aimed to understand how alfalfa responds to Al stress by identifying and analyzing Al-stress-responsive genes in alfalfa roots at the whole-genome scale. The transcriptome changes in alfalfa roots under Al stress for 4, 8, or 24 h were analyzed using Illumina high-throughput sequencing platforms. A total of 2464 differentially expressed genes (DEGs) were identified, and most were up-regulated at early (4 h) and/or late (24 h) Al exposure time points rather than at the middle exposure time point (8 h). Metabolic pathway enrichment analysis demonstrated that the DEGs involved in ribosome, protein biosynthesis, and process, the citrate cycle, membrane transport, and hormonal regulation were preferentially enriched and regulated. Biosynthesis inhibition and signal transduction downstream of auxin- and ethylene-mediated signals occur during alfalfa responses to root growth inhibition. The internal Al detoxification mechanisms play important roles in alfalfa roots under Al stress. These findings provide valuable information for identifying and characterizing important components in the Al signaling network in alfalfa and enhance understanding of the molecular mechanisms underlying alfalfa responses to Al stress.

Highlights

Aluminum (Al) is a light metal and the third most abundant element in the earth’s crust (Ma, 2005)
In order to gain a general overview of the gene expression profiles of alfalfa roots under Al stress, four cDNA libraries representing one control (C, without Al stress) and three treatments at different time points (A4, A8, and A24) were designed for high-throughput RNA-Seq, and a total of 221,271,740 raw reads were obtained (Table 1)
We analyzed the transcript profiles of alfalfa roots in response to Al stress by using the Illumina deep sequencing system and identified a total of 75,903 unigenes in the four sample libraries, which was more than previously reported for alfalfa root transcriptome analyses (Postnikova et al, 2013)

Summary

Introduction

Aluminum (Al) is a light metal and the third most abundant element in the earth’s crust (Ma, 2005). In the tropical and subtropical regions, Al toxicity has been considered as the major factor limiting crop production in acidic soils, which account for 40% of the world’s arable land (Kochian et al, 2005). The application of large quantities of lime always used to alleviate the soil Al toxicity and sustain the crop production. This practice is expensive and being unsustainable and not environmentally friendly. Understanding the nature of Al tolerance mechanisms in plants and developing cultivars with improved tolerance to acidic soil stress is an appealing approach to addressing this issue

Objectives

Methods

Results

Conclusion