Salt cress. A halophyte and cryophyte Arabidopsis relative model system and its applicability to molecular genetic analyses of growth and development of extremophiles.
Salt cress (Thellungiella halophila) is a small winter annual crucifer with a short life cycle. It has a small genome (about 2 x Arabidopsis) with high sequence identity (average 92%) with Arabidopsis, and can be genetically transformed by the simple floral dip procedure. It is capable of copious seed production. Salt cress is an extremophile native to harsh environments and can reproduce after exposure to extreme salinity (500 mm NaCl) or cold to -15 degrees C. It is a typical halophyte that accumulates NaCl at controlled rates and also dramatic levels of Pro (>150 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. Leaves of salt cress are more succulent-like, have a second layer of palisade mesophyll cells, and are frequently shed during extreme salt stress. Roots of salt cress develop both an extra endodermis and cortex cell layer compared to Arabidopsis. Salt cress, although salt and cold tolerant, is not exceptionally tolerant of soil desiccation. We have isolated several ethyl methanesulfonate mutants of salt cress that have reduced salinity tolerance, which provide evidence that salt tolerance in this halophyte can be significantly affected by individual genetic loci. Analysis of salt cress expressed sequence tags provides evidence for the presence of paralogs, missing in the Arabidopsis genome, and for genes with abiotic stress-relevant functions. Hybridizations of salt cress RNA targets to an Arabidopsis whole-genome oligonucleotide array indicate that commonly stress-associated transcripts are expressed at a noticeably higher level in unstressed salt cress plants and are induced rapidly under stress. Efficient transformation of salt cress allows for simple gene exchange between Arabidopsis and salt cress. In addition, the generation of T-DNA-tagged mutant collections of salt cress, already in progress, will open the door to a new era of forward and reverse genetic studies of extremophile plant biology.
Inan
Günsu
G
Center for Plant Environmental Stress Physiology, Purdue University, West Lafayette, Indiana 47907-2010, USA.
Zhang
Quan
Q
Li
Pinghua
P
Wang
Zenglan
Z
Cao
Ziyi
Z
Zhang
Hui
H
Zhang
Changqing
C
Quist
Tanya M
TM
Goodwin
S Mark
SM
Zhu
Jianhua
J
Shi
Huazhong
H
Damsz
Barbara
B
Charbaji
Tarif
T
Gong
Qingqiu
Q
Ma
Shisong
S
Fredricksen
Mark
M
Galbraith
David W
DW
Jenks
Matthew A
MA
Rhodes
David
D
Hasegawa
Paul M
PM
Bohnert
Hans J
HJ
Joly
Robert J
RJ
Bressan
Ray A
RA
Zhu
Jian-Kang
JK
D000040:Abscisic Acid / Q000494:pharmacology; D000064:Acclimatization; D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D001483:Base Sequence; D019607:Brassicaceae / Q000166:cytology / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D002453:Cell Cycle; D003080:Cold Temperature; D005020:Ethyl Methanesulfonate / Q000494:pharmacology; D018745:Genome, Plant; D008969:Molecular Sequence Data; D018517:Plant Roots / Q000235:genetics; D018520:Plant Shoots / Q000235:genetics; D012621:Seasons; D012689:Sequence Homology, Nucleic Acid; D012965:Sodium Chloride / Q000494:pharmacology
D012965:Sodium Chloride; D000040:Abscisic Acid; D005020:Ethyl Methanesulfonate