Mol. Cells 29, 1-10, January 31, 2010
Identification of an Arabidopsis Nodulin-Related
Protein in Heat Stress
Qiantang Fu1,2, Shujia Li1, and Diqiu Yu1,*
We identified a Nodulin-related protein 1 (NRP1) encoded
by At2g03440, which was previously reported to be RPS2
interacting protein in yeast-two-hybrid assay. Northern
blotting showed that AtNRP1 expression was suppressed
by heat stress (42°C) and induced by low temperature
(4°C) treatment. Strong GUS staining was observed in the
sites of meristematic tissues of pAtNRP1:: GUS transgenic
plants, such as shoot apex and root tips, young leaf veins,
stamens and stigmas of flowers, and abscission layers of
young siliques. To study AtNRP1 biological functions, we
have characterized both loss-of-function T-DNA insertion
and transgenic overexpression plants for AtNRP1 in
Arabidopsis. The T-DNA insertion mutants displayed no
obvious difference as compared to wild-type Arabidopsis
under heat stress, but the significant enhanced suscepti-
bility to heat stress was revealed in two independent
AtNRP1-overexpressing transgenic lines. Further study
found that the decreased thermtolerance in AtNRP1-
overexpressing lines accompanied significantly decreased
accumulation of ABA after heat treatment, which was
probably due to AtNRP1 playing a role in negative-feedback
regulation of the ABA synthesis pathway. These results
support the viewpoint that the application of ABA inhibits
nodulation and nodulin-related gene expression and threaten
adverse ambient temperature can impact the nodulin-related
Plants are exposed to various environmental stresses during
their growth and development. Among these stresses, high
temperature is one of the major problems that limit the growth
and distribution of plants (Boyer, 1982). On the other hand,
plants have evolved various mechanisms for adapting to the
effects of heat shock (HS). Accumulation of heat shock proteins
(HSPs), membrane compositional changes necessary for main-
tenance of functional integrity, and activation of oxidative de-
fensive systems are involved in improving plant thermotoler-
ance (Kaplan et al., 2004; Kotak et al., 2007b; Locato et al.,
2008; Queitsch et al., 2000; Sung et al., 2001). Transcription
activation of HSPs genes is regulated by heat shock transcrip-
tion factors (HSFs) through binding to heat shock promoter
elements (HSEs) in the promoter regions of HSPs genes during
heat stress (Baniwal et al., 2004; Yamamoto et al., 2005). In
addition, the induction of abscisic acid (ABA), salicylic acid (SA),
and calcium-based signaling pathways were reported to be
involved in heat-stress adaptation (Clarke et al., 2004; Larkin-
dale and Knight, 2002; Larkindale et al., 2005; Liu et al., 2008).
Exogenous application of these signaling agents to plants can
also result in some degree of enhanced thermotolerance
(Larkindale and Knight, 2002). These multiple responses sug-
gest that many alternative processes are involved in thermotol-
erance. Plants at various growth stages respond differently to
heat stress, suggesting a link between development and
thermotolerance (Hong et al., 2003).
The infection of the plant by rhizobia bacteria is a complex
process which a number of plant genes take part in. Legumes
form a specialized organ termed the nodule via the expression
of their genes that encode proteins named ‘nodulins’ when the
leguminous plants were elicited by the secretion of bacterial
effectors called nod factors in their root hairs (Stougaard, 2000).
For non-nodule plants, Arabidopsis, when the plant roots have
been colonized by several specific strains of Pseudomonas
spp., they would develop a protective defense response that is
called rhizobacteria-mediated induced systemic resistance
(Cartieaux et al., 2003). Recent study has indicated that
abscisic acid (ABA) can not only inhibit Nod factor signal trans-
duction and promote or suppress resistance against various
pathogens (de Torres-Zabala et al., 2007; Ding et al., 2008;
Mohr and Cahill, 2007), but also can break a new signaling
pathway to heat stress (Larkindale and Huang, 2004; Larkin-
dale et al., 2005). A transient peak in ABA levels was reported
in response to HS in pea plants (Liu et al., 2006) and during
recovery from HS treatments in creeping bentgrass (Larkindale
and Huang, 2004). It has been reported that ABA induces
thermotolerance in cell-suspension cultures of Bromus inermis
Leyss. (Robertson et al., 1994), and ABA pretreatment can
increase cell viability and growth upon HS (Zhang and Fe-
vereiro, 2007). In addition, the overexpression of transcription
factor ABF3 in ABA signaling induced high-temperature toler-
ance in transgenic Arabidopsis (Kim et al., 2004). These results
suggested that ABA could also be involved in the response to
heat stress. Moreover, genotypes with a putative high ABA
1Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming 650223, People’s
Republic of China, 2Graduate School of the Chinese Academy of Sciences, Beijing 100039, People’s Republic of China
Received August 14, 2009; revised September 24, 2009; accepted September 25, 2009; published online December 7, 2009
Keywords: abscisic acid (ABA), heat stress, nodulin-related protein 1, thermotolerance
8 A Nodulin-Related Protein in Heat Stress
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