Learning from evolution: Thellungiella generates new knowledge on essential and critical components of abiotic stress tolerance in plants

Abstract

Thellungiella salsuginea (halophila) is a close relative of Arabidopsis thaliana but, unlike A. thaliana, it grows well in extreme conditions of cold, salt, and drought as well as nitrogen limitation. Over the last decade, many laboratories have started to use Thellungiella to investigate the physiological, metabolic, and molecular mechanisms of abiotic stress tolerance in plants, and new knowledge has been gained in particular with respect to ion transport and gene expression. The advantage of Thellungiella over other extremophile model plants is that it can be directly compared with Arabidopsis, and therefore generate information on both essential and critical components of stress tolerance. Thellungiella research is supported by a growing body of technical resources comprising physiological and molecular protocols, ecotype collections, expressed sequence tags, cDNA-libraries, microarrays, and a pending genome sequence. This review summarizes the current state of knowledge on Thellungiella and re-evaluates its usefulness as a model for research into plant stress tolerance.

Keywords: Brassica; abiotic/environmental stress; adaptation - evolutionary; comparative genomics; gene expression; ion channels.

Figure 1.

The ‘Real’ Thellungiella halophila (Bayanaul) Growing in the Glasshouse of the Vrije University of Amsterdam. Seeds supplied by D.A. German (Botanical Institute Barnaul, Russia). Photo by A.H. de Boer.

Figure 2.

Typical Rosette of (A) Arabidopsis thaliana (Col0) and (B) Thellungiella salsuginea (Shandong) Grown in Low-Salt Hydroponic Culture with 10 and 14 h Daylight, Respectively. Photos by V. Martínez, University of Glasgow.

Figure 3.

Thellungiella salsuginea (Yukon) Growing in the Laboratory and its Natural Field Site in the Yukon Territory in Canada. Upper left: Chamber-grown plant showing terminal flowers and prominent rosette. Photo by E.A. Weretilnyk, McMaster University. Upper right: Yukon field site in May 2006. Photo by J. Dedrick, McMaster University. Bottom: Yukon field site in July 2005. Photo by J. Dedrick, McMaster University.

Figure 4.

Effective Exclusion of Na⁺ from the Shoot of Thellungiella (Shandong) Is Achieved through the Combined Action of a Voltage-Independent Channel (VIC) and a Na⁺/H⁺ Antiporter (SOS1). VIC has higher selectivity for K⁺ over Na⁺ than the respective system in Arabidopsis, thereby limiting Na⁺ influx into root cells and maintaining a negative membrane potential that activates K⁺ inward rectifying channels and high-affinity transport systems. SOS1 exports Na⁺ from the root tip and xylem, thereby limiting its transport into the root elongation zone and the shoot. For details and references, see text.

Figure 5.

Technical Approaches to Study the Physiology and Molecular Biology of Thellungiella (Shandong). (A) Micro-grafted hybrid plants comprising shoots of wild-type Thellungiella and roots of luciferase-transformed Arabidopsis thaliana plants (graft and photo by G. Littlejohn, University of Glasgow). (B) Patch clamp recordings of picoAmpere-currents passing through distinctly opening and closing single ion channels in the plasma membrane of Thellungiella root protoplasts (recording by V. Volkov, University of Glasgow). (C) Visualization of the epidermal cells of Thellungiella roots transiently expressing Yellow Fluorescent Protein (YFP) linked to the ER marker gene HDEL after transfection with Agrobacterium rhizogenes (photo by P. Camapanoni, University of Glasgow).