Chemistry Reference
In-Depth Information
we compact it here that CIPK1/3/8/14/15/20/23/24 take part in ABA signaling. CIPKs play a
main role in plant ion homeostasis and abiotic stress tolerance by regulating H
+
, Na
+
, Ca
2+
and NO
3
-
transporters and K
+
channels and interacting with TFs (Kudla, J. et al., 2010).
Moreover, the CDPKs that are involved in ABA signaling are CPK3/4/6/11/32. CPK4 and
CPK11 are closely related genes and both phosphorylate the transcription factors ABF1 and
ABF4. Based on a majority of evidence, it can be concluded that CDPKs target core ABA
signaling components (Geiger, et al., 2010). A role for MAPKs in ABA signaling has been
shown above, but posted here again (MPK1/2/3/6/9/12). Taken together, none of these
protein kinase families function specifically in ABA signaling, which still need us to stress
on functional redundancy and complicated cross-talk network in the future research.
As follows, we take a brief look at other kinases. CDKs (Cyclin dependent protein kinases)
are a large family of serine/threonine protein kinases and mainly function in ensuring that
cells progress in order over the different cell division stages. But their roles in abiotic stress
responses turn out to be more eye-catching, which can be reflected in heat, cold, drought
and salt stimuli researches (reviewed by Georgios Kitsios, 2011). Other findings like Somatic
Embryogenesis Receptor Kinase (SERK) relating to somatic embryogenesis and apomixis
(Marcelo O. Santos et al., 2009), AtNEK6, a member of the NIMA (never in mitosis A)-
related kinases (NEKs) (Lee SJ et al., 2010), bring us a large amount of information to explore
the functional importance of various kinases in abiotic stress.
2.4.3. Protein phosphatases
During phosphorylation process, the job for protein phosphatases is to remove the
phosphate added by protein kinases. Based on their substrate specificity, protein
phosphatases can be classified, at least three families, as PPP family and PPM family
composed by serine/threonine phosphatases, PTP family comprising tyrosine phosphatases,
and dual specificity phosphatases (dsPTPs/dsPPase). As the largest group of phosphatases
in plants, serine/threonine phosphatases can be further divided into PP1, PP2A, PP2B, and
PP2C. For stress signal transduction, involvement of PP2C, PP2A, PTP, dsPPase have been
reported in ABA or stress signal transduction, but the best-known example is the PP2C. On
the other hand, many experiments have found that the relationship between MAPKs and
phosphatases both exists in animals and plants. It has been shown that tyrosine-specific
phosphorylation is associated with plant MAPKs, which again demonstrate the essential
position phosphatases take in signaling pathways.
For the biggest branch of protein phosphatases in plants, in Arabidopsis alone, 76 PP2C
genes have been identified early (Kerk et al. 2002). Further researches say ABA and other
abiotic stress stimuli can induce A-type PP2C expression. Furthermore the A-type PP2C
phosphatases, ABI1, ABI2, HAB1 (P2CHA) and PP2CA (AHG3) have been proved to
directly interact with PYR/RCAR ABA receptors, however they always act as negative
regulators at different layers of ABA signaling. (Merlot et al., 2001; Umezawa et al., 2009;
Nishimura et al., 2010).
