Transcriptome Comparison Reveals the Adaptive Evolution of Two Contrasting Ecotypes of Zn/Cd Hyperaccumulator Sedum alfredii Hance.

Qianying Yang,M J I Shohag,Xiaoe Yang,Zhenli He,Ying Feng

doi:10.3389/fpls.2017.00425

Abstract

Hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of Sedum alfredii Hance belong to the same species but exhibit contrasting characteristics regarding hyperaccumulation and hypertolerance to cadmium and zinc. The Illumina Hiseq 2500 platform was employed to sequence HE and NHE to study the genetic evolution of this contrasting trait. Greater than 90 million clean reads were obtained and 118,479/228,051 unigenes of HE/NHE were annotated based on seven existing databases. We identified 149,668/319,830 single nucleotide polymorphisms (SNPs) and 12,691/14,428 simple sequence repeats (SSRs) of HE/NHE. We used a branch-site model to identify 18 divergent orthologous genes and 57 conserved orthologous genes of S. alfredii Hance. The divergent orthologous genes were mainly involved in the transcription and translation processes, protein metabolism process, calcium (Ca2+) pathway, stress response process and signal transduction process. To the best of our knowledge, this is the first study to use RNA-seq to compare the genetic evolution of hyperaccumulating and non-hyperaccumulating plants from the same species. In addition, this study made the sole concrete for further studies on molecular markers and divergent orthologous genes to depict the evolution process and formation of the hyperaccumulation and hypertolerance traits in S. alfredii Hance.

Highlights

Given long-term evolution and natural selection, a few plants growing in mining soils for a long period of time exhibit strong tolerance and hyperaccumulation of heavy metals within a translocation factor >1
Hyperaccumulating ecotype (HE) accumulated greater than 20,000 mg/kg Zn in shoots when supplied with 100 μM Zn for 7 days, and its shoots accumulated more than 3,500 mg/kg Cd when supplied with 50 μM Cd
Zn was mainly stored in roots of non-hyperaccumulating ecotype (NHE), whereas HE, Zn and Cd are mainly transported to shoots (Figures 1B,C)

Summary

Introduction

Given long-term evolution and natural selection, a few plants growing in mining soils for a long period of time exhibit strong tolerance and hyperaccumulation of heavy metals within a translocation factor >1. These plants are called hyperaccumulator plants (Baker and Brooks, 1989). 9,000 mg/kg (Yang et al, 2002, 2004) Another ecotype of S. alfredii is not tolerant to heavy metal, with shoot Zn concentrations of only 490 mg/kg and leaf Cd concentrations of 533 mg/kg (Ni et al, 2004; Xiong et al, 2004)

Methods

Results

Discussion

Conclusion