Biotechnology for mechanisms that counteract salt stress in extremophile species: A genome-based view

Molecular genetics has confirmed older research and generated new insights into the ways how plants deal with adverse conditions. This body of research is now being used to interpret stress behavior of plants in new ways, and to add results from most recent genomics-based studies. The new knowledge now includes genome sequences of species that show extreme abiotic stress tolerances, which enables new strategies for applications through either molecular breeding or transgenic engineering. We will highlight some physiological features of the extremophile lifestyle, outline emerging features about halophytism based on genomics, and discuss conclusions about underlying mechanisms. © 2012 Korean Society for Plant Biotechnology and Springer

A comparative study of salt tolerance parameters in 11 wild relatives of Arabidopsis thaliana

Salinity is an abiotic stress that limits both yield and the expansion of agricultural crops to new areas. In the last 20 years our basic understanding of the mechanisms underlying plant tolerance and adaptation to saline environments has greatly improved owing to active development of advanced tools in molecular, genomics, and bioinformatics analyses. However, the full potential of investigative power has not been fully exploited, because the use of halophytes as model systems in plant salt tolerance research is largely neglected. The recent introduction of halophytic Arabidopsis-Relative Model Species (ARMS) has begun to compare and relate several unique genetic resources to the well-developed Arabidopsis model. In a search for candidates to begin to understand, through genetic analyses, the biological bases of salt tolerance, 11 wild relatives of Arabidopsis thaliana were compared: Barbarea verna, Capsella bursa-pastoris, Hirschfeldia incana, Lepidium densiflorum, Malcolmia triloba, Lepidium virginicum, Descurainia pinnata, Sisymbrium officinale, Thellungiella parvula, Thellungiella salsuginea (previously T. halophila), and Thlaspi arvense. Among these species, highly salt-tolerant (L. densiflorum and L. virginicum) and moderately salt-tolerant (M. triloba and H. incana) species were identified. Only T. parvula revealed a true halophytic habitus, comparable to the better studied Thellungiella salsuginea. Major differences in growth, water transport properties, and ion accumulation are observed and discussed to describe the distinctive traits and physiological responses that can now be studied genetically in salt stress research

Use of Arabidopsis thaliana and its close relative Thellungiella halophila to reveal abiotic stress determinants

Salt cress (Thellungiella halophila), a halophyte, is a close relative of Arabidopsis that can be used as molecular genetic model in salt tolerance studies. It has many desirable characteristics to be a model plant such as such as small genome size, short life cycle, high seed yield and efficient transformation. Salt cress is an extremophile native to harsh environments and can reproduce after exposure to extreme salinity (500 mM NaCl) or cold to -15°C. It is a typical halophyte that accumulates NaCl at controlled rates and also dramatic levels of proline (\u3e150 mM) during exposure to high salinity. Stomata of salt cress are distributed on the leaf surface at higher density but are less open than the stomata of Arabidopsis and respond to salt stress by closing more tightly. In this research we present a detailed physiological characterization of this model plant focusing on its applicability to molecular genetic analyses of growth and development of extremophiles. Moreover we report the identification of two Arabidopsis T-DNA tagged mutants. The shs1-1 (sodium hyper sensitive) mutant was generated as second site mutation in the sos3-1 background and isolated as sos3 enhancer. The shs1 mutation has pleiotropic effects on seedling development such as altered leaf mophology, sucrose hypersensitivity and ABA insensitivity. SHS1 encodes a putative adenylate translocator-like protein and subcellular localization of SHS1 indicates endoplasmic reticulum. The second mutant isolated is hos6-1 (for high expression of osmotically responsive genes) in which expression of RD29A::LUC was hyperactivated by ABA, salinity stress and low temperature. hos6-1 plants displayed a significant increase in tolerance to soil dehydration. The basta resistance of hos6-1 cosegregates with the ABA hypersensitive phenotypes indicating that the responsible mutation results from an insertion of the T-DNA carrying the BAR gene. HOS6 appears to play an important role in ABA signaling and response to dehydration stress

Genome Structures and Halophyte-Specific Gene Expression of the Extremophile Thellungiella parvula in Comparison with Thellungiella salsuginea (Thellungiella halophila) and Arabidopsis1[W]

The genome of Thellungiella parvula, a halophytic relative of Arabidopsis (Arabidopsis thaliana), is being assembled using Roche-454 sequencing. Analyses of a 10-Mb scaffold revealed synteny with Arabidopsis, with recombination and inversion and an uneven distribution of repeat sequences. T. parvula genome structure and DNA sequences were compared with orthologous regions from Arabidopsis and publicly available bacterial artificial chromosome sequences from Thellungiella salsuginea (previously Thellungiella halophila). The three-way comparison of sequences, from one abiotic stress-sensitive species and two tolerant species, revealed extensive sequence conservation and microcolinearity, but grouping Thellungiella species separately from Arabidopsis. However, the T. parvula segments are distinguished from their T. salsuginea counterparts by a pronounced paucity of repeat sequences, resulting in a 30% shorter DNA segment with essentially the same gene content in T. parvula. Among the genes is SALT OVERLY SENSITIVE1 (SOS1), a sodium/proton antiporter, which represents an essential component of plant salinity stress tolerance. Although the SOS1 coding region is highly conserved among all three species, the promoter regions show conservation only between the two Thellungiella species. Comparative transcript analyses revealed higher levels of basal as well as salt-induced SOS1 expression in both Thellungiella species as compared with Arabidopsis. The Thellungiella species and other halophytes share conserved pyrimidine-rich 5′ untranslated region proximal regions of SOS1 that are missing in Arabidopsis. Completion of the genome structure of T. parvula is expected to highlight distinctive genetic elements underlying the extremophile lifestyle of this species

Biotechnology for mechanisms that counteract salt stress in extremophile species: a genome-based view

Molecular genetics has confirmed older research and generated new insights into the ways how plants deal with adverse conditions. This body of research is now being used to interpret stress behavior of plants in new ways, and to add results from most recent genomics-based studies. The new knowledge now includes genome sequences of species that show extreme abiotic stress tolerances, which enables new strategies for applications through either molecular breeding or transgenic engineering. We will highlight some physiological features of the extremophile lifestyle, outline emerging features about halophytism based on genomics, and discuss conclusions about underlying mechanisms. © 2012 Korean Society for Plant Biotechnology and Springer