Protein Kinases and Phosphatases Involved in ABA Signaling - Abscisic Acid: Metabolism, Transport and Signaling - page 135

CaM-like domain induces a conformational change that releases the auto-inhibi-
tion (Harper et al. 2004 ; Harper and Harmon 2005 ). This results in kinase activ-
ity, enabling CDPK autophosphorylation as well as the phosphorylation of target
substrates (Liese and Romeis 2013 ). Besides Ca 2 + , phosphorylation, lipids, and
interaction with 14-3-3 proteins have been reported to further modulate CDPKs
in vitro (Harper et al. 2004 ; Harper and Harmon 2005 ; Klimecka and Muszynska
2007 ; Cheng et al. 2002b ; Ludwig et al. 2004 ; Witte et al. 2010 ; Klimecka et al.
2011 ). This working model was supported and refined by recent structural analysis
(Wernimont et al. 2010 , 2011 ; Schulz et al. 2013 ; Hamel et al. 2014 ).
The CDPKs are encoded by a large multigene family, which is divided into
four subgroups (Harmon et al. 2000 ; Cheng et al. 2002b ). The Arabidopsis
genome encodes 34 CDPK members, rice ( Oryza sativa ) encodes 29 members,
wheat ( Triticum aestivum ) encodes 20 members, maize ( Zea mays ) encodes 35
members, and poplar ( Populus trichocarpa ) encodes 30 members (Harmon et al.
2000 ; Asano et al. 2005 ; Li et al. 2008 ; Ma et al. 2013 ; Zuo et al. 2013 ). The
large gene-family-encoded CDPKs implicate possible redundancy and/or diver-
sity in their functions (Harmon et al. 2001 ; Cheng et al. 2002b ; Boudsocq and
Sheen 2013 ; Hamel et al. 2014 ). Growing evidence indicates that CDPKs regu-
late many aspects in plant growth and development as well as plant adaptation to
biotic and abiotic stresses (Bachmann et al. 1995 , 1996 ; McMichael et al. 1995 ;
Pei et al. 1996 ; Sheen 1996 ; Li et al. 1998 ; Sugiyama et al. 2000 ; Romeis et al.
2001 ; Hrabak et al. 2003 ; Shao and Harmon 2003 ; McCubbin et al. 2004 ; Choi
et al. 2005 ; Ivashuta et al. 2005 ; Mori et al. 2006 ; Yu et al. 2007 ; Zhu et al. 2007 ;
Zou et al. 2010 ; Asano et al. 2011 , 2012 ; Brandt et al. 2012 ; Boudsocq and Sheen
2013 ; Ding et al. 2013 ; Liese and Romeis 2013 ; Liu et al. 2013 ). In plant hormone
signaling, CDPKs are believed to be important regulators to be involved in various
signaling pathways (Cheng et al. 2002b ; Ludwig et al. 2004 ; Asano et al. 2012 ;
Boudsocq and Sheen 2013 ).
The CDPK isoforms are expressed differently in plant organs/tissues (Harper
et al. 2004 ; Ray et al. 2007 ; Li et al. 2008 ; Wan et al. 2007 ) with some members
expressed in most organs whereas others specifically in some tissues. The expres-
sion profiles or kinase activities of the CDPK members were reported to be modi-
fied in response to diverse stimuli, including abscisic acid (ABA), cold, drought,
salinity, heat, elicitors, and pathogens (Romeis et al. 2001 ; Ray et al. 2007 ; Li
et al. 2008 ; Wan et al. 2007 ; Abbasi et al. 2004 ; Yu et al. 2006 , Zhu et al. 2007 ).
CDPK members have been showed to be localized to diverse cellular compart-
ments, including the cytosol, nucleus, plasma membrane, endoplasmic reticulum,
tonoplast, mitochondria, chloroplasts, oil bodies, and peroxisomes (Boudsocq
et al. 2010 ; Zou et al. 2010 ; Li et al. 2008 ; Myers et al. 2009 ; Yu et al. 2006 ; Zhu
et al. 2007 ; Lu and Hrabak 2002 ; Benetka et al. 2008 ; Mehlmer et al. 2010 ; Choi
et al. 2005 ; Coca and San Segundo 2010 ). This diversity of subcellular localization
indicates that CDPKs have access to a plethora of potential substrates through-
out the plant cell. In recent years, biochemical analyses, together with genetic
approaches, have identified CDPK substrates that are involved in diverse cellular
processes, such as primary and secondary metabolism, stress responses, ion and