Abstract
Understanding the molecular mechanisms that convey salt tolerance in plants is a crucial issue for increasing crop yield. The ice plant (Mesembryanthemum crystallinum) is a halophyte that is capable of growing under high salt conditions. For example, the roots of ice plant seedlings continue to grow in 140 mM NaCl, a salt concentration that completely inhibits Arabidopsis thaliana root growth. Identifying the molecular mechanisms responsible for this high level of salt tolerance in a halophyte has the potential of revealing tolerance mechanisms that have been evolutionarily successful. In the present study, deep sequencing (RNAseq) was used to examine gene expression in ice plant roots treated with various concentrations of NaCl. Sequencing resulted in the identification of 53,516 contigs, 10,818 of which were orthologs of Arabidopsis genes. In addition to the expression analysis, a web-based ice plant database was constructed that allows broad public access to the data. The results obtained from an analysis of the RNAseq data were confirmed by RT-qPCR. Novel patterns of gene expression in response to high salinity within 24 hours were identified in the ice plant when the RNAseq data from the ice plant was compared to gene expression data obtained from Arabidopsis plants exposed to high salt. Although ABA responsive genes and a sodium transporter protein (HKT1), are up-regulated and down-regulated respectively in both Arabidopsis and the ice plant; peroxidase genes exhibit opposite responses. The results of this study provide an important first step towards analyzing environmental tolerance mechanisms in a non-model organism and provide a useful dataset for predicting novel gene functions.
Highlights
High salinity is a critical problem in crop production that results in reduced plant growth and a significant reduction in productivity
These results indicate that, ice plant is tolerant to higher salt concentrations than Arabidopsis, similar morphological changes in roots are observed in both species when they are subjected to high salt conditions
The high levels of salt tolerance, present in some wild species of plants, present an excellent resource to study the adaptive mechanisms that form the basis of salt tolerance, and such plants may provide a valuable source of genes that can be used to improve salt tolerance in agronomic crops
Summary
High salinity is a critical problem in crop production that results in reduced plant growth and a significant reduction in productivity. Studies using Arabidopsis as a model plant have identified a number of genes involved in salt tolerance. DREB2A orthologs in other plant species, such as rice, soybean, poplar, buffalograss, and sugarcane, appear to be involved in salt tolerance [2], [3], [4], [5], [6]. These studies have demonstrated that the DREB2A gene regulatory network is an important molecular mechanism for salt tolerance in the Plant Kingdom. Additional data from Arabidopsis have revealed cross-talk of the DREB2A pathway with other pathways, such as the ABA-mediated signaling, osmotic response, and some ionic response pathways that are induced by exposure to high salt [1]
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