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BackgroundWild barley is adapted to highly diverse environments throughout its geographical distribution range. Transcriptome sequencing of differentially adapted wild barley ecotypes from contrasting environments contributes to the identification of genes and genetic variation involved in abiotic stress tolerance and adaptation.ResultsTwo differentially adapted wild barley ecotypes from desert (B1K2) and Mediterranean (B1K30) environments were analyzed for drought stress response under controlled conditions. The desert ecotype lost more water under both irrigation and drought, but exhibited higher relative water content (RWC) and better water use efficiency (WUE) than the coastal ecotype. We sequenced normalized cDNA libraries from drought-stressed leaves of both ecotypes with the 454 platform to identify drought-related transcripts. Over half million reads per ecotype were de novo assembled into 20,439 putative unique transcripts (PUTs) for B1K2, 21,494 for B1K30 and 28,720 for the joint assembly. Over 50% of PUTs of each ecotype were not shared with the other ecotype. Furthermore, 16% (3,245) of B1K2 and 17% (3,674) of B1K30 transcripts did not show orthologous sequence hits in the other wild barley ecotype and cultivated barley, and are candidates of ecotype-specific transcripts. Over 800 unique transcripts from each ecotype homologous to over 30 different stress-related genes were identified. We extracted 1,017 high quality SNPs that differentiated the two ecotypes. The genetic distance between the desert ecotype and cultivated barley was 1.9-fold higher than between the Mediterranean ecotype and cultivated barley. Moreover, the desert ecotype harbored a larger proportion of non-synonymous SNPs than the Mediterranean ecotype suggesting different demographic histories of these ecotypes.ConclusionsThe results indicate a strong physiological and genomic differentiation between the desert and Mediterranean wild barley ecotypes and a closer relationship of the Mediterranean to cultivated barley. A significant number of novel transcripts specific to wild barley were identified. The higher SNP density and larger proportion of SNPs with functional effects in the desert ecotype suggest different demographic histories and effects of natural selection in Mediterranean and desert wild barley. The data are a valuable genomic resource for an improved genome annotation, transcriptome studies of drought adaptation and a source of new genetic markers for future barley improvement.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-995) contains supplementary material, which is available to authorized users.

Regulation of the rate of transpiration is an important part of plants' adaptation to uncertain environments. Stomatal closure is the most common response to severe drought. By closing their stomata, plants reduce transpiration to better their odds of survival under dry conditions. Under mild to moderate drought conditions, there are several possible transpiration patterns that balance the risk of lost productivity with the risk of water loss. Here, we hypothesize that plant ecotypes that have evolved in environments characterized by unstable patterns of precipitation will display a wider range of patterns of transpiration regulation along with other quantitative physiological traits (QPTs), compared to ecotypes from less variable environments. We examined five accessions of wild barley (Hordeum vulgare ssp. spontaneum) from different locations in Israel (the B1K collection) with annual rainfall levels ranging from 100 to 900 mm, along with one domesticated line (cv. Morex). We measured several QPTs and morphological traits of these accessions under well-irrigated conditions, under drought stress and during recovery from drought. Our results revealed a correlation between precipitation-certainty conditions and QPT plasticity. Specifically, accessions from stable environments (very wet or very dry locations) were found to take greater risks in their water-balance regulation than accessions from areas in which rainfall is less predictable. Notably, less risk-taking genotypes recovered more quickly than more risk-taking ones once irrigation was resumed. We discuss the relationships between environment, polymorphism, physiological plasticity and fitness, and suggest a general risk-taking model in which transpiration-rate plasticity is negatively correlated with population polymorphism.

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