Siberian wildrye (Elymus sibiricus) is a xero-mesophytic forage grass with high nutritional quality and stress tolerance. Among its numerous germplasm resources, some possess superior drought resistance. In this study, we firstly investigated the physiological differences between the leaves of drought-tolerant (DT) and drought-sensitive (DS) genotypes under different field water contents (FWC) in soil culture. The results showed that, under drought stress, DT maintained a lower leaf water potential for water absorption, sustained higher photosynthetic efficiency, and reduced oxidative damage in leaves by efficiently maintaining the ascorbic acid-glutathione (ASA-GSH) cycle to scavenge reactive oxygen species (ROS) compared to DS. Secondly, using RNA sequencing (RNA-seq), we analyzed the gene expression profiles of DT and DS leaves under osmotic stress of hydroponics induced by PEG-6000. Through differential analysis, we identified 1226 candidate unigenes, from which we subsequently screened out 115/212 differentially expressed genes (DEGs) that were more quickly induced/reduced in DT than in DS under osmotic stress. Among them, Unigene0005863 (EsSnRK2), Unigene0053902 (EsLRK10) and Unigene0031985 (EsCIPK5) may be involved in stomatal closure induced by abscisic acid (ABA) signaling pathway. Unigene0047636 (EsCER1) may positively regulates the synthesis of very-long-chain (VLC) alkanes in cuticular wax biosynthesis, influencing plant responses to abiotic stresses. Finally, the contents of wax and cutin were measured by GC-MS under osmotic stress of hydroponics induced by PEG-6000. Corresponding to RNA-seq, contents of wax monomers, especially alkanes and alcohols, showed significant induction by osmotic stress in DT but not in DS. It is suggested that limiting stomatal and cuticle transpiration under drought stress to maintain higher photosynthetic efficiency and water use efficiency (WUE) is one of the critical mechanisms that confer stronger drought resistance to DT. This study provides some insights into the molecular mechanisms underlying drought tolerance in E. sibiricus. The identified genes may provide a foundation for the selection and breeding of drought-tolerant crops.

The leaf wax characteristics of Dryas octopetala and Saxifraga oppositifolia, collected from the high Arctic semi-desert of Svalbard, Norway (79 degrees N, 13 degrees E), were compared and differences in their wax composition related to winter snow cover. The leaf wax composition of the winter-green D. octopetala differed from that of the herbaceous S. oppositifolia in that high abundances of the triterpenoids, ursolic acid, oleanoic acid and uvaol, were observed in D. octopetala extracts but not in S. oppositifolia extracts. D. octopetala leaf waxes were consistently lower in n-alkanes and in n-alkanols compared to the leaf waxes of S. oppositifolia. Leaf waxes of both species from snow-free, wind-swept microsites had significantly higher abundances of n-alkanes than in those plants growing in adjacent, swale areas where snow accumulates in winter. It is hypothesized that this higher abundance of n-alkanes may be due to a response to a greater degree of dessication, lower temperatures and lower soil moisture experienced by plants on the snow-free ridge microsites during leaf expansion. In order to test whether these biochemical and anatomical attributes might change in response to short term alterations in winter climate, snow fences were erected on ridge sites. The wax attributes of ridge plants exposed to a single year of increased winter snow cover were examined and the n-alkane composition of leaf waxes were observed to be more like those of plants growing in adjacent swale areas than for those of ridge plants growing in unmanipulated areas. This shift in leaf wax composition implies that environmental differences during leaf development can have an influence on final leaf wax composition.