Plant Science 158 2000 147 – 154
A ditelosomic line of ‘Chinese Spring’ wheat with augmented acquired thermotolerance
Patrick O’Mahony, John Burke
Plant Stress and Germplasm De6elopment Unit, USDA-ARS,
3810 4
th Street, Lubbock, TX
79415
, USA Received 18 April 2000; received in revised form 9 June 2000; accepted 9 June 2000
Abstract
A study of the ditelosomic series of ‘Chinese Spring’ wheat has yielded a number of lines displaying either an increased or decreased ability to acquire thermotolerance. One such ditelosomic DT is termed DT1BS which refers to the missing short arm
of chromosome 1 in the B genome. The DT1BS line has the ability to acquire thermotolerance at lower induction temperatures and provide greater protection to the plant against otherwise lethal elevated temperatures. Using a chlorophyll accumulation assay
to measure plant health, we show that DT1BS accumulates chlorophyll optimally at the same temperature, and to similar levels as ‘Chinese Spring’. We also show that maximum acquired thermotolerance against a 48°C challenge is induced at 40°C, but
significant levels of protection can be obtained at temperatures as low as 34°C in DT1BS or 36°C in ‘Chinese Spring’. Heat-shock protein accumulation is observed in DT1BS at temperatures 4°C lower than the ‘Chinese Spring’ and is correlated with the
induction of acquired thermotolerance. © 2000 Elsevier Science Ireland Ltd. All rights reserved.
Keywords
:
Acquired thermotolerance; Heat shock proteins; Chinese Spring wheat; Ditelosomics www.elsevier.comlocateplantsci
1. Introduction
Plants are frequently exposed to elevated soil and air temperatures resulting in a reduction in
their growth, development and ultimately produc- tivity. When subjected to a period of sub-lethal
elevated temperatures, plants acquire thermotoler- ance which transiently raises the injury threshold
and protects them from subsequent, otherwise lethal, high temperatures. This acquisition of ther-
motolerance is a complex physiological phe- nomenon which has been shown to involve at least
some heat shock proteins HSPs.
Plants, like all organisms, produce HSPs in re- sponse to various environmental stresses [1 – 3]. At
sub-lethal elevated temperatures quantitative in- duction of HSPs occurs with a concomitant reduc-
tion in the synthesis of many other proteins. This alteration in metabolic priorities coincides with the
acquisition of thermotolerance [1,4,5]. Significant evidence is available from yeast studies which link
HSP induction to the acquisition of thermotoler- ance [6 – 8]. However, to date only HSP101 has
been directly linked to acquired thermotolerance in plants [9,10]. In Arabidopsis modulated heat
shock protein synthesis as well as heat shock factor activity and expression have been shown to
correlate with levels of thermotolerance [11 – 14]. Studies in thermo-susceptible and thermo-tolerant
recombinant inbred lines of wheat detected a ge- netic relationship between expression of a plastid
localized HSP26 and acquired thermotolerance [15]. In addition, other studies have demonstrated
that an acquired thermotolerance-deficient yeast that carries a mutated HSP104 gene can be suc-
cessfully complemented by plant HSP 101 genes from soybean [16] and Arabidopsis [17].
Expression of HSP genes is regulated primarily at the transcriptional level [13]. Upon heat shock
Abbre6iations
:
DT, ditelosomic; HSP, heat shock protein; SDS, sodium dodecyl sulphate.
Corresponding author. Tel: + 1-806-7495560; fax: + 1-806- 7235272.
E-mail address
:
jburkelbk.ars.usda.gov J. Burke. 0168-945200 - see front matter © 2000 Elsevier Science Ireland Ltd. All rights reserved.
PII: S 0 1 6 8 - 9 4 5 2 0 0 0 0 3 1 5 - 0
latent constitutive heat shock factor HSF is trimerized, causing it to bind to heat shock ele-
ments HSEs upstream of the HSP gene [18]. Efficient transcription of heat shock genes occurs
when 5’ proximal tripartite HSEs bind trimerized HSF. This interaction is enhanced by other se-
quence motifs and possibly acts on the chromatin to enable access to transcription factors such as
HSF and TATA box binding proteins [18]. Multi- ple HSFs have been reported in plants and verte-
brates while for Drosophila and yeast only one has been identified. Control of HSF trimerization
and thus transcription of HSP genes in many higher eukaryotes is controlled by C-terminal hy-
drophobic repeats, but these areas are not well conserved in plants or yeasts. Also in higher eu-
karyotes, it is proposed that phosphorylation along with feedback control by HSP70 and HSP90
act to repress HSF activity [19].
Obtaining direct evidence to link HSPs with acquired thermotolerance in higher plants has
been restricted due to a lack of functional muta- tions with which a cause and effect relationship
could be established. We have begun an investiga- tion of heat shock responses in aneuploid genetic
stocks of ‘Chinese Spring’ wheat where specific chromosomal deletions result in a reduction or
up-regulation of acquired thermotolerance coin- ciding with an alteration of HSP synthesis.
In this study we used a sensitive chlorophyll accumulation assay [20] to characterize the ac-
quired thermotolerance of one of a series of ditelo- somics DT a plant missing one chromosome
arm-telocentric of the hexaploid wheat cultivar ‘Chinese Spring’ [21]. A previous investigation us-
ing 2-D gel electrophoresis [23] to analyze the genetic control of HSP synthesis in wheat iden-
tified the chromosomal localization of genes con- trolling a number of low molecular mass HSPs.
Variations in relative HSP levels suggested that the homeologous DT lines 3, 4 and 7 contain the
majority of the controlling genes indicating chro- mosomes 3, 4 and 7 as sites containing HSP
controlling loci. However, the study did not ad- dress the possible functional relationship between
specific HSP changes and levels of acquired thermotolerance.
Here we characterize the DT1BS line of wheat which had previously been observed to possess
greater acquired thermotolerance than ‘Chinese Spring’ [22]. We demonstrate that an up-regula-
tion of HSP synthesis in DT1BS at lower induc- tion temperatures correlates with acquisition of
thermotolerance, suggesting that the missing arm may contain at least one form of genetic control
for HSP synthesis and acquired thermotolerance in ‘Chinese Spring’ wheat.
2. Materials and methods
