New Insights into Desiccation-Associated Gene Regulation by Lilium longiflorum ASR during Pollen Maturation and in Transgenic Arabidopsis - International Review of Cell and Molecular Biology - page 71

Most genes that respond to environmental stimuli such as drought, cold,
and salt stresses are also induced by exogenous ABA treatment ( Cai et al.,
2011 ). In vegetative tissues, a rapid increase in ABA levels promotes stoma-
tal closure and prevents stomatal opening, thereby reducing transpirational
water loss under water stress conditions. During late embryogenesis, ABA
promotes the acquisition of desiccation tolerance and seed dormancy, and
inhibits seed germination ( Fujita et al., 2011 ; Koornneef et al., 2002 ; Seiler
et al., 2011 ). In addition, ABA can hasten the initiation of fruit ripening
( Chen et al., 2011 ).
A sizable amount of literature has been published on the characteriza-
tion of ABA signal transduction cascades ( Cutler et al., 2010 ; Fujita et al.,
2011 ; Hubbard et al., 2010 ; Liu, 2012 ). ABA-responsive gene expression
is regulated by transcription factors, receptors, protein kinase, phosphatase,
chromatin-remodeling factors, and secondary messengers, such as Ca 2+ ,
cADPR, and inositol triphosphate, which have been implicated in ABA-
mediated responses ( Lemtiri-Chlieh et al., 2003 ; Roelfsema and Hedrich,
2010 ; Viswanathan and Zhu, 2002 ). Moreover, ABA signaling is regulated by
mRNA maturation and stability, microRNA levels, nuclear specking, and
protein degradation ( Nonogaki, 2010 ; Xie et al., 2005 ). Thus, ABA signaling
is clearly involved in a complex network of both positively and negatively
regulating components.
Although the expression of the DS2 gene in potato ( Solanum tuberosum )
is ABA-independent ( Dóczi et al., 2005 ), Asr genes are typically upregulated
by ABA upon dehydration ( Huang et al., 2000 ; Philippe et al., 2010 ; Silhavy
et al., 1995 ), salt ( Dai et al., 2011 ; Kalifa et al., 2004b ; Yang et al., 2005 ),
and cold treatments ( Hsu et al., 2011 ; Kim et al., 2009 ; Schneider et al.,
1997 ). Asr genes also respond to pathogen attacks ( Liu et al., 2010 ; Muñiz
et al., 2012 ). In addition, Asr genes have been suggested to play impor-
tant roles in plant developmental processes, such as senescence ( Jeanneau
et al., 2002 ), pollen maturation ( Wang et al., 1998 ), flowering ( Dóczi et al.,
2005 ; Gilad et al., 1997 ), flower ( Dóczi et al., 2005 ; Gilad et al., 1997 ), fruit
development ( Cakir et al., 2003 ; Canel et al., 1995 ; Chen et al., 2011 ), and
glucose metabolism ( Cakir et al., 2003 ; Frankel et al., 2007 ; Saumonneau
et al., 2012 ; Shkolnik and Bar-Zvi, 2008 ). Recently, Arenhart et al. (2012)
indicated that the ASR5 gene is differentially regulated in the aluminum-
tolerant rice and the obtained ASR-RNAi plants exhibit aluminum sus-
ceptibility. The ectopic overexpression of LLA23 and MpAsr in transgenic
Arabidopsis is insensitive to ABA and increases plant tolerance to drought
and salt stresses ( Dai et al., 2011 ; Yang et al., 2005 ). In addition, ectopic