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Thermotolerance Generated by Plant/Fungal Symbiosis

Authors:
Regina S Redman at University of Washington Seattle
Regina S Redman
Kathy B. Sheehan at Indiana University Bloomington
Kathy B. Sheehan
Richard G Stout
Richard G Stout
Richard G Stout
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Rusty J. Rodriguez
Rusty J. Rodriguez
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Abstract

Two angiotensin II (Ang II)–specific receptors, AGTR1 and AGTR2, are expressed in the mammalian brain. Ang II actions on blood pressure regulation, water electrolyte balance, and hormone secretion are primarily mediated by AGTR1. The function of AGTR2 remains unclear. Here, we show that expression of the AGTR2 gene was absent in a female patient with mental retardation (MR) who had a balanced X;7 chromosomal translocation. Additionally, 8 of 590 unrelated male patients with MR were found to have sequence changes in theAGTR2 gene, including one frameshift and three missense mutations. These findings indicate a role for AGTR2 in brain development and cognitive function.
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ECOLOGY
Thermotolerance Generated by
Plant/Fungal Symbiosis
Regina S. Redman,
1,2
Kathy B. Sheehan,
3,5
Richard G. Stout,
4,5
Russell J. Rodriguez,
1,2
* Joan M. Henson
3,5
All plants studied in natural ecosystems are
symbiotic with fungi (1), which obtain nu-
trients while either positively, negatively,
or neutrally affecting host fitness (2). Plant
adaptation to selective pressures is consid-
ered to be regulated by the plant genome
(3). To test whether mutualistic fungi con-
tribute to plant adaptation, we collected
200 Dichanthelium lanuginosum plants
from geothermal soils at 10 sites in Lassen
Volcanic (LVNP) and Yellowstone (YNP)
National Parks. These soils have annual
temperature fluctuations ranging from
about 20° to 50°C (4 ).
Plants and their roots were removed and as-
sessed for fungal colonization (5). A fungal
endophyte was isolat-
ed from the roots,
crowns, leaves, and
seed coats of all plants
collected. Cultures es-
tablished from single
spores were analyzed
by morphological (6)
and rDNA sequence
analyses (7) that sug-
gested that the endo-
phyte may be a new
species of Curvularia
(5). Soils from the
base of 30 plants in
YNP were devoid of
the Curvularia sp., al-
though other fungi
were abundant (4).
Moreover, axenically
cultured Curvularia
sp. was incapable of
mycelial growth, spore
germination, or surviv-
al at ⱖ40°C (5). Be-
cause geothermal soils
were above 40°C all
summer (4) and de-
void of the fungus, we conclude that this Curvu-
laria sp., like all known Curvularia species, is
exclusively associated with plants.
To assess the effect of the endophyte on
the thermotolerance of D. lanuginosum,we
removed seed coats and surface sterilized
seeds (8) to generate endophyte-free plants.
Treated seeds were planted in sterile ma-
genta boxes containing sand, and after 1
month, plants were either mock-inoculated
or inoculated with Curvularia sp. by pipet-
ting 10
5
spores between the crown and first
leaf. In the absence of thermal stress, en-
dophyte-colonized (symbiotic) and endo-
phyte-free (nonsymbiotic) plants showed
no measurable growth or developmental
differences. When root zones were heated
with thermal tape (Fig. S1), nonsymbiotic
plants (45/45) became shriveled and chlo-
rotic at 50°C (Fig. 1A). In contrast, symbi-
otic plants (45/45) tolerated constant 50°C
soil temperature for 3 days and intermittent
soil temperatures as high as 65°C for 10
days. All nonsymbiotic plants (45/45) died
during the 65°C heat regime, whereas sym-
biotic plants (45/45) survived. The endo-
phyte was reisolated from surface sterilized
roots and leaves of all surviving plants,
indicating that both the fungus and the host
were protected from thermal stress.
We also field-tested symbiotic and non-
symbiotic seedlings in pasteurized geother-
mal soil collected and returned to Amphi-
theater Springs (YNP) in May 2001 (Fig.
1B). By May 2002, symbiotic plants were
greener with greater root and leaf masses (Ta-
ble S2) than those of nonsymbiotic plants in
soils ⱕ40°C. In soils above 40°C, nonsymbi-
otic plants did not survive while symbiotic
plants thrived. The beneficial effect of fungal
symbiosis increased with soil temperatures,
demonstrating that Curvularia sp. provided
thermal protection for D. lanuginosum. We rei-
solated Curvularia sp. from D. lanuginosum
roots at 45°C field soil temperatures, indicat-
ing that thermal protection was also provided
to the fungus, which corroborated our labo-
ratory experiments.
In addition to thermotolerance, the basis of
mutualism in this system may involve other
benefits (e.g., nutrient acquisition by the fun-
gus). Several possible symbiotic mechanisms
could confer thermotolerance. In planta, the
fungal endophyte produces cell wall melanin
(Fig. S3) that may dissipate heat along the
hyphae and/or complex with oxygen radicals
generated during heat stress (9). Alternatively,
the endophyte may act as a “biological trigger”
allowing symbiotic plants to activate stress-
response systems more rapidly and strongly
than nonsymbiotic plants (10).
References and Notes
1. O. Petrini, in Microbiology of the Phyllosphere,N.J.
Fokkema, J. van den Heuvel, Eds. (Cambridge Univ.
Press, Cambridge, 1986), pp. 175–187.
2. D. H. Lewis, in The Biology of Mutualism,D.H.
Boucher, Ed. (Croom Helm, London, 1985), pp. 29 –
39.
3. M. F. Smallwood, C. M. Calvert, D. J. Bowles, Eds.,
Plant Responses to Environmental Stress (BIOS Scien-
tific Publishers, Oxford, 1999).
4. R. S. Redman, A. Litvintseva, K. B. Sheehan, J. M.
Henson, R. J. Rodriguez, Appl. Environ. Microbiol. 65,
5193 (1999).
5. Materials and Methods are available as supporting
material on Science Online.
6. A. Sivanesan, Mycol. Pap. 158, 104 (1987).
7. T. J. White, T. Bruns, S. Lee, J. Taylor, in PCR
Protocols: A Guide to Methods and Applications,
M. A. Innis, D. H. Gelfand, J. J. Sninsky, T. J. White,
Eds. (Academic Press, San Diego, CA, 1990), pp.
315–322.
8. R. S. Redman, D. D. Dunigan, R. J. Rodriguez, New
Phytol. 151, 705 (2001).
9. J. F. Davidson, B. Whyte, P. H. Bissinger, R. H. Schiestl,
Proc. Natl. Acad. Sci. U.S.A. 93, 5116 (1996).
10. R. S. Redman et al., Plant Physiol. 119, 795 (1999).
11. We thank T. Al-Niemi, L. Brasche, M. Bateson, E.
Kuhn, A. Litvintseva, and J. Duda for technical and
field assistance. This project was made possible by
the permission, assistance, and guidelines of YNP and
LVNP. This work was supported by grants from the
U.S. Geological Survey, the NSF (9977922), the U.S.
Army Research Office (DAAHO4-96-1-01194), and
the MSU Thermal Biology Institute.
Supporting Online Material
www.sciencemag.org/cgi/content/full/298/5598/1581/
DC1
Materials and Methods
Figs. S1 and S3
Table S2
1
U.S. Geological Survey, WFRC, 6505 NE 65th Street,
Seattle, WA 98115, USA.
2
Department of Botany,
University of Washington, Seattle, WA 98195, USA.
3
Department of Microbiology,
4
Department of Plant
Sciences, and
5
Thermal Biology Institute, Montana
State University, Bozeman, MT 59717, USA.
To whom correspondence should be addressed. E-
mail: Rusty_Rodriguez@usgs.gov
Fig. 1. Representative symbiotic (with Curvularia sp.) and nonsymbiotic
D. lanuginosum plants with rhizosphere temperatures of 50°C for 3 days
or 65°C for 8 hours/day for 10 days under laboratory conditions (A) and
in 40° or 45°C soil under field conditions (B).
B REVIA
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  • BRAIN RES
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A novel GC-rich human macrosatellite VNTR in Xq24 is differentially methylated on active and inactive X chromosomes
Article
  • Jun 1992
A new X chromosome-specific repetitive sequence, a 3 kilobase HindIII clone with a base composition of 63% C+G, has been isolated. The sequence is organized as a hypervariable tandem repeat cluster ranging in size from 150-350 kilobases, with outlying single copies. This locus, designated DXZ4 and mapped to chromosome band Xq24, may consist of as many as 50 variable-length alleles. It represents a class of variable number of tandem repeat polymorphism which may be termed 'macrosatellite'. The cluster is highly methylated on the active X chromosome and hypomethylated on the inactive X.
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Behavioral and cardiovascular effects of disrupting the angiotensin II type-2 receptor in mice
Article
  • Nov 1995
Angiotensin II, a potent regulator of blood pressure and of water and electrolyte balance, binds to two different G-protein-coupled receptors. The type-1 receptor (AT1) mediates the vasopressive and aldosterone-secreting effects of angiotensin II, but the function of the type-2 receptor (AT2) is unknown, although it is expressed in both adult and embryonic life. To address this question, we have generated mice lacking the gene encoding the AT2 receptor. Mutant mice develop normally, but have an impaired drinking response to water deprivation as well as a reduction in spontaneous movements. Their baseline blood pressure is normal, but they show an increased vasopressor response to injection of angiotensin II. Thus, although the AT2 receptor is not required for embryonic development, it plays a role in the central nervous system and cardiovascular functions that are mediated by the renin-angiotensin system.
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Angiotensin II receptor subtypes in the human central nervous system
Article
  • Apr 1995
  • BRAIN RES
The distribution of the AT1 and AT2 subtypes of angiotensin II receptor was mapped in the adult human central nervous system using quantitative in vitro autoradiography. Binding in all forebrain, midbrain, pontine, medullary and spinal cord sites where angiotensin II receptors have previously been described is of the AT1 subtype, as is binding in the small and large arteries in the adjacent meninges and in choroid plexus. By contrast, both AT1 and AT2 receptors occur in the molecular layer of the cerebellum. Angiotensin II AT1 receptors in the brain show a moderate degree of conservation across mammalian species studied so far, whereas expression of AT2 receptors is more variable, and is more restricted in the human CNS than in many other mammals. These differences between the subtype distributions in humans and other animals indicate the need for care when extrapolating the results of animal studies involving the brain angiotensin system.
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Alterations in angiotensin AT1 and AT2 receptor subtype levels in brain regions from patients with neurodegenerative disorders
Article
  • Mar 1996
  • EUR J PHARMACOL
The present studies assessed the levels of [125I][Sar1,ILE8]angiotensin II-labelled angiotensin AT1 and AT2 receptor recognition sites in homogenates of various brain areas (including caudate nucleus, putamen, substantia nigra, hippocampus, frontal cortex, temporal cortex and cerebellum) from patients with clinically diagnosed Parkinson's disease, Huntington's disease and Alzheimer's disease and those from age-, sex- and post-mortem delay-matched neurologically and psychiatrically normal patients. Radiolabelled angiotensin AT1 receptor recognition site levels were significantly decreased by approximately 70%, 70% and 90% in the caudate nucleus, putamen and substantia nigra, respectively, from patients with Parkinson's disease relative to matched controls. Furthermore, radiolabelled angiotensin AT2 receptor levels were decreased by some 60% in the caudate nucleus of patients with Parkinson's disease relative to control patients. In brain tissue homogenates from patients with Huntington's disease, the angiotensin AT1 receptor recognition site levels were decreased by approximately 30% in putamen relative to the control patients whilst angiotensin AT2 receptor levels were increased by some 90% in the caudate nucleus relative to the control patients. In brain tissue homogenates from patients with Alzheimer disease, the angiotensin AT2 receptor recognition site levels were significantly increased by approximately 200% in the temporal cortex relative to the control patients. The present results indicate that the reduction of angiotensin AT1 and/or AT2 receptor recognition site levels in the caudate nucleus, putamen and substantia nigra correlates with the principal neuropathology associated with Parkinson's disease and as such indicates that at least a significant population of angiotensin AT1 and AT2 receptors are located on the human dopaminergic nigrostriatal pathway. In addition, the marked increase in the levels of angiotensin AT2 receptor recognition sites in temporal cortex from patients with Alzheimer's disease correlates with some other markers associated with the renin-angiotensin system previously investigated in tissue from patients with this neurological disease.
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