Halophytes as a source of salt tolerance genes and mechanisms: a case study for the Salt Lake area, Turkey

The worst case scenario of global climate change predicts both drought and salinity would be the first environmental factors restricting agriculture and natural ecosystems, causing decreased crop yields and plant growth that would directly affect human population in the next decades. Therefore, it is vital to understand the biology of plants that are already adapted to these extreme conditions. In this sense, extremophiles such as the halophytes offer valuable genetic information for understanding plant salinity tolerance and to improve the stress tolerance of crop plants. Turkey has ecological importance for its rich biodiversity with up to 3700 endemic plants. Salt Lake (Lake Tuz) in Central Anatolia, one of the largest hypersaline lakes in the world, is surrounded by salty marshes, with one of the most diverse floras in Turkey, where arid and semiarid areas have increased due to low rainfall and high evaporation during the summer season. Consequently, the Salt Lake region has a large number of halophytic, xerophytic and xero-halophytic plants. One good example is Eutrema parvulum (Schrenk) Al-Shehbaz & Warwick, which originates from the Salt Lake region, can tolerate up to 600mM NaCl. In recent years, the full genome of E. parvulum was published and it has been accepted as a model halophyte due to its close relationship (sequence identity in range of 90%) with Arabidopsis thaliana (L. Heynh.). In this context, this review will focus on tolerance mechanisms involving hormone signalling, accumulation of compatible solutes, ion transporters, antioxidant defence systems, reactive oxygen species (ROS) signalling mechanism of some lesser-known extremophiles growing in the Salt Lake region. In addition, current progress on studies conducted with E. parvulum will be evaluated to shed a light on future prospects for improved crop tolerance.