Abstract
BackgroundAmmopiptanthus mongolicus is the only evergreen broadleaf shrub in the northwest desert of China, which can survive long-term aridity and extremely cold environments. In order to understand the genetic mechanisms underlying stress tolerance and adaptation to unfavorable environments of woody plants, an EST approach was used to investigate expression patterns of A. mongolicus in response to abiotic stresses.ResultsESTs were generated from a cDNA library constructed from A. mongolicus seedlings subjected to cold and drought stresses. Analysis of 5,637 cDNA sequences led to the identification of 5,282 ESTs and 1,594 unigenes, which were denoted as the AmCDUnigene set. Of these, 70% of unigenes were annotated and classified into 12 functional categories according to Gene Ontology, and 30% of unigenes encoded unknown function proteins, suggesting some of them were novel or A. mongolicus specific genes. Using comparative analysis with the reported genes from other plants, 528 (33%) unigenes were identified as stress-responsive genes. The functional classification of the 528 genes showed that a majority of them are associated with scavenging reactive oxygen species, stress response, cellular transport, signal transduction and transcription. To further identify candidate abiotic stress-tolerance genes, the 528 stress-responsive genes were compared with reported abiotic stress genes in the Comparative Stress Genes Catalog of GCP. This comparative analysis identified 120 abiotic stress-responsive genes, and their expression in A. mongolicus seedlings under cold or drought stress were characterized by qRT-PCR. Significantly, 82 genes responded to cold and/or drought stress. These cold- and/or drought-inducible genes confirmed that the ROS network, signal transduction and osmolyte accumulation undergo transcriptional reorganization when exposed to cold or drought stress treatments. Additionally, among the 1,594 unigenes sequences, 155 simple sequence repeats (SSRs) were identified.ConclusionThis study represents a comprehensive analysis of cold and/or drought stress-responsive transcriptiome of A. mongolicus. The newly characterized genes and gene-derived markers from the AmCDUnigene set are valuable resources for a better understanding of the mechanisms that govern stress tolerance in A. mongolicus and other related species. Certain up-regulated genes characterizing these processes are potential targets for breeding for cold and/or drought tolerance of woody plants.
Highlights
Ammopiptanthus mongolicus is the only evergreen broadleaf shrub in the northwest desert of China, which can survive long-term aridity and extremely cold environments
The quality of the cDNA Library Since we aimed to identify both early and late coldresponsive and/or drought-responsive genes through expressed sequence tags (ESTs) analysis, a cDNA library, AmCDL (A. mongolicus cold- and drought-responsive library), was constructed from pooled samples of A. mongolicus seedlings at different stages of cold treatment and water deficit
Eighty-five percent of detected genes (82 of 97 detected genes) were found cold- or drought-inducible, confirming the AmCDUnigene data in some cases. These genes could be involved in multiple pathways, such as the reactive oxygen species network, photosynthesis, stress response, transcriptional regulation, signal transduction, etc., which probably all participate in stress tolerance improvement of A. mongolicus
Summary
Ammopiptanthus mongolicus is the only evergreen broadleaf shrub in the northwest desert of China, which can survive long-term aridity and extremely cold environments. In order to understand the genetic mechanisms underlying stress tolerance and adaptation to unfavorable environments of woody plants, an EST approach was used to investigate expression patterns of A. mongolicus in response to abiotic stresses. The proliferation of woody plants in arid and high latitude deserts is essential for sustainable conservation and amelioration of environments. Genetic improvement of forest trees for tolerance to environmental stresses such as drought, high salinity, low temperature and heat is a promising approach for the future of environmental conservation. It is vital to know how plants respond to environmental stresses and which biochemical pathways and genes are involved in stress tolerance. Molecular mechanisms by which woody plants respond to abiotic stresses remain poorly understood despite their biological and practical importance
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