Chemistry Reference
In-Depth Information
Ca
2+
-and Ca
2+
/CaM-dependent protein kinases (CCaMKs), some DNA or lipid binding
proteins, and a few enzymes (Day et al., 2002; Yang and Poovaiah, 2003; Harper and
Harmon, 2005). Many calcium sensors are coded by multiple genes, and expression of many
of these is induced by stresses (DeFalco et al., 2010).
Then, let's take a look at what will be the next move of those Ca
2+
-activated sensors. Firstly,
they can directly bind to
cis
-elements in the promoters of specific genes and induce or
repress their expression. Secondly, they will choose to bind to DNA binding proteins and
activate or inactivate them, thereby resulting in activation or repression of gene expression.
The third path belongs to the activated Ca
2+
-regulated protein kinases (CDPK,CaM binding
protein kinase (CBK), CIPK and CCaMK) or phosphatases. They phosphorylate/
dephosphorylate a transcription factor (TF), respectively, resulting in activation or
repression of transcription, which allow for the perception and transmission of Ca
2+
signatures directly into phosphorylation cascades that orchestrate downstream signaling
responses (Weinl and Kudla, 2009). The most well-known TFs involved in the
phosphorylation include Calmodulin binding transcription activators (CAMTAs; also
referred to as signal-responsive proteins or ethylene-induced CaM binding proteins) (Reddy
et al., 2000), MYB family (Popescu et al., 2007), the WRKY family (Park et al., 2005; Popescu
et al., 2007), basic leucine zipper (bZIP) TFs, like TGA3 (Szymanski et al., 1996) and ABA-
responsive TFs ABF1, 2, 3, and 4 (reviewed in Galon et al., 2010), and CBP60s who is a plant-
specific CaM binding proteins family (Reddy et al., 1993; Zhang et al., 2010), as well as
members of NAC family (Kim et al., 2007; Yoon et al., 2008). However they are TFs binding
to Ca
2+
/CaM under Ca
2+
regulation, so we posted here another two TFs who can directly
bind Ca
2+
. One is encoded by
Arabidopsis NaCL-INDUCED GENE (NIG)
(Kim, J., and Kim,
H.Y., 2006), and the other is At-CaM7 (Kushwaha et al., 2008). In sum, Ca
2+
and their
interacting proteins served as the upstream elements play an important role in regulating of
some stress genes expression.
Meanwhile, what performance they will give in each specific abiotic stress condition needs
to be simply introduced here. For drought stress, cellular Ca
2+
transmits drought signals to
regulate the physiological responses induced by drought stress (Dai et al., 2007). It has been
found that Ca
2+
treatment increased protection against membrane lipid peroxidation and
stability of membranes and therefore resulted in the increase of drought resistance of rice
seedlings. It is also reported that in wheat Ca
2+
may reduce the adverse stress effects by
elevating the content of proline and glycine betaine, thus improving the water status and
growth of seedlings and minimizing the injury to membranes (Geisler et al., 2000; Munns et
al., 2006; Goldgur et al., 2007). Additionally, Ca
2+
/CaM means a lot to the process of ABA-
induced drought signal transferring under PEG stress. And ABA synthesis correlates with
cytoplasmic Ca
2+
concentrations ([Ca
2+
]
cyt
) (Rabbani et al., 2003; Noctor, 2006). We know how
important ABA is to the stomatal status, and now more studies have established a close
relationship between [Ca
2+
]
cyt
oscillation and stomatal status. In addition, in Arabidopisis
genome, 9 SOS3 homologs (SCaBP/CBL) and 22 SOS2 homologs (SOS2-like protein kinases -
PKS/CBL-interacting protein kinases-CIPK) were identified. By the way, SOS2 is a
