Extreme environmental conditions limit plant growth and impose abiotic stress to plants. Land degradation, including desertification, drought and salinity affects around one third of the global land surface (Jarraud 2005). Adaptation of plants to suboptimal conditions requires extensive physiological and molecular reprogramming, leading to major changes in metabolic, proteomic and transcript profiles.
Research on model organisms such as Arabidopsis thaliana and application of system biology approaches has identified a number of genes and regulatory hubs which control the networks linking stress perception and metabolic or developmental responses (Ahuja et al. 2010). However, study of a stress sensitive model has limitations in understanding tolerance to harsh environments. Extremophile plants, such as xerophytes and halophytes can grow in arid regions or on saline soils, which are otherwise lethal to nonadapted species. Halophytes represent 1% of all plant species; can optimally thrive in the presence of 50–250mM NaCl, whilst some withstand salt concentrations up to 600mM NaCl (Flowers and Colmer 2008). While the physiology of halophytes has been extensively studied, molecular regulation of the extremophile character still remains to be understood. Eutrema salsugineum (previously called Thellungiella salsuginea) is a salt tolerant relative of Arabidopsis, which has been used in a number of comparative studies to reveal the genetic and molecular basis of halophytism (Amtmann 2009). Natural genetic variability of extremophiles is an attractive genetic resource to improve tolerance of crops to adverse environments (Nevo and Chen 2010). Transfer of tolerance traits to other species is however usually hampered by incompatibility. Transformation of genomic or cDNA libraries can facilitate random gene transfer between different species. Examples include a cDNA library of E. salsugineum, expressed in Arabidopsis, leading to the identification of several Eutrema genes which improved salt tolerance (Du et al. 2008). A binary bacterial artificial chromosome library was used to transfer large genomic fragments of E. salsugineum to Arabidopsis and screen for salt tolerance (Wang et al. 2010).
Here, we describe the novel version of the Conditional cDNA Overexpressing System (COS), which was developed to randomly transfer and express cDNA clones in Arabidopsis under the control of a chemically inducible promoter system (Papdi et al. 2008; Rigó et al. 2012). The cDNA library was derived from the less-known halophyte of the Brassicaceae family Lepidium crassifolium, which naturally grows on salty-sodic soils in Central Europe and Asia. Random transfer and overexpression of L. crassifolium cDNA in Arabidopsis could facilitate the identification of novel tolerance genes. Here, we demonstrate that regulated expression of several L. crassifolium cDNA could enhance salt, osmotic or oxidative stress tolerance of Arabidopsis. The COS system is therefore suitable for interspecific gene transfer and can be employed to identify valuable genes from less-known wild species
