1. Protein Kinases Primary elements in signal transduction
- Phosphorylated residues by protein kinases: S, T, Y
A Protein kinase can ⓟ hundreds of target proteins,
thereby amplifying signals.
- Activator of Protein Kinases:
light,
pathogen,
growth regulators,
temperature change,
nutrition deprivation,
water stresses (drought, salt), etc

2. The various classes of protein kinases found in plants.
Ex) PKA, PKC
GSK3, CKII

3. Cell Surface Receptors May Have Catalytic Activity
Receptor Tyrosine Kinases
Receptor Tyrosine Phosphatases
Receptor Ser/Thr Kinases
Tyrosine linked receptors
Receptor guanylate cyclases
cell surface proteases

4. Ligand Binding to Receptor Tyrosine Kinases
Induces autophosphorylation
Signaling Proteins That Bind to RTKs
Are Activated by phosphorylation

5. Receptor-Like Kinases (RLKs)
S-domain RLKs
2. Leucine rich repeat (LRR) RLKs
3. Epidermal growth factor (EGF)-like RLKs
4. Lectin receptor kinases

6. S receptor kinase (SRK)
Plant Receptor-like Kinases Are Structurally Similar to Animal Receptor Tyrosine Kinases
S receptor kinase (SRK)
The first class is characterized by an extracellular S domain
The S domain was identified in S locus glycoproteins (SLGs) which regulate self-incompatibility in Brassica species.

7. An example of S-domain RLK
Fig
General model for pollen tube incompatibility as a result of
two way signaling between pollen tube and stigma.

8. 2. Leucine-rich repeat (LRR) receptors
They were first identified as disease resistance genes that may play key roles in the cell surface recognition of ligands
Plant LRR receptors have been implicated in normal developmental functions as well.
(in cell–cell recognition during pollination, in shape and size of organs)
Brassinosteroid receptor has been identified as an LRR receptor

9. An example of LRR RLKs Fig. 18.60 Model of a homodimeric receptor-like
protein kinase, RLK5, binding its ligand
and undergoing autophosphorylation

10. 3. Receptors with EGF (epidermal growth factor)–like repeat
This type of RLK that contains an epidermal growth factor–like repeat has been identified in Arabidopsis.
Receptor PRO25 is localized in the chloroplast and interacts with a light harvesting chlorophyll a/b–binding protein (LHCP).

11. An example of EGF-Like RLK
An example of Lectine RLK

13. Figure 14.24 The MAPK cascade.
Hormonal stimulation of the receptor tyrosine kinase leads to the activation of Raf, also known as MAP kinase kinase kinase (MAPKKK).

14. Fig 18.63 Many signals are transduced by protein kinase cascades
that regulate gene expression
Siganls: Auxin, GA, ABA, touch, wind,
osmotic stress, wounding, elicitor
Raf-1L kinase: CTR1 in ethylene signaling

15. Protein Phosphatase ◆ PP1 ◆ PP2A ◆ PP2B (calcineurin, CaM-dependent)
◆ PP2C: abi in ABA signaling
◆ PP inhibitor can prevent
red light, proliferation, growth
factors, pollen tube signaling
Fig18.64
Structure of FK506, rapamycin
and cyclosporine.

16. Ethylene-signaling mutants have striking phenotypes.
Fig
Ethylene-signaling mutants have striking phenotypes.
ETR1: the receptor of ethylene
CTR1: negative regulator of ethylene signaling

17. Fig 18.22
Transgenic plants expressing variants of the etr1-1 gene.

18. Fig18. 66
Comparison of ethylene signaling pathway and animal Ras-signaling pathway

19. ABA signaling in plantsNO
NADPH Oxidase
ROS (H2O2)
Ca2+ Channel open
[Ca2+]
ABI1 (PP2C)
K+ channel, Cl- channel
Reduction of Turgor pressure

20. Fig 18.71
Some of the known interactions in the plant cell signal transduction network.