Abstract
The response and adaption to salt remains poorly understood for beach morning glory [Ipomoea imperati (Vahl) Griseb], one of a few relatives of sweetpotato, known to thrive under salty and extreme drought conditions. In order to understand the genetic mechanisms underlying salt tolerance of a Convolvulaceae member, a genome-wide transcriptome study was carried out in beach morning glory by 454 pyrosequencing. A total of 286,584 filtered reads from both salt stressed and unstressed (control) root and shoot tissues were assembled into 95,790 unigenes with an average length of 667 base pairs (bp) and N50 of 706 bp. Putative differentially expressed genes (DEGs) were identified as transcripts overrepresented under salt stressed tissues compared to the control, and were placed into metabolic pathways. Most of these DEGs were involved in stress response, membrane transport, signal transduction, transcription activity and other cellular and molecular processes. We further analyzed the gene expression of 14 candidate genes of interest for salt tolerance through quantitative reverse transcription PCR (qRT-PCR) and confirmed their differential expression under salt stress in both beach morning glory and sweetpotato. The results comparing transcripts of I. imperati against the transcriptome of other Ipomoea species, including sweetpotato are also presented in this study. In addition, 6,233 SSR markers were identified, and an in silico analysis predicted that 434 primer pairs out of 4,897 target an identifiable homologous sequence in other Ipomoea transcriptomes, including sweetpotato. The data generated in this study will help in understanding the basics of salt tolerance of beach morning glory and the SSR resources generated will be useful for comparative genomics studies and further enhance the path to the marker-assisted breeding of sweetpotato for salt tolerance.
Highlights
Salt and drought stresses are two major abiotic constraints to furthering crop food production
The ability to further abiotic stress breeding in sweetpotato is plausible given the availability of Next generation sequencing (NGS) as a low-cost, large-scale approach for transcriptome sequencing [43]; as a result an increased knowledge of functional genes has been identified for sweetpotato [3–5,39]
Little information has been derived from the previous reports on the changes in its transcriptome in response to abiotic stress; to our knowledge all existing transcriptome libraries developed were from tissues at different developmental stages except for a single library from drought stressed leaves [39]
Summary
Salt and drought stresses are two major abiotic constraints to furthering crop food production. Generation sequencing (NGS) has been utilized to unravel genes and pathways on a transcriptome-wide scale in nonmodel plant species For example, 454 and Illumina platforms have benefited the transcriptome analysis of sweetpotato by identifying genes involved in the development of storage roots (4) and documenting functional transcripts on a global scale [5,6]. None of these studies has focused on transcriptome and gene expression profiling of sweetpotato under salinity stress. Transcriptome profiling by generation sequencing technologies are being widely applied in the study to identify components that mediate abiotic stress responses in plants, from wild and non-model plants [7–9]
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