The Arabidopsis protein kinase PTI1-2 is activated by convergent phosphatidic acid and oxidative stress signaling pathways downstream of PDK1 and OXI1.
Arabidopsis PDK1 activity is regulated by binding to the lipid phosphatidic acid (PA) resulting in activation of the oxidative stress-response protein kinase OXI1/AGC2-1. Thus there is an inferred link between lipid signaling and oxidative stress signaling modules. Among a panel of hormones and stresses tested, we found that, in addition to PA, the fungal elicitor xylanase activated PDK1, suggesting that PDK1 has a role in plant pathogen defense mechanisms. The downstream OXI1 was activated by additional stress factors, including PA, H(2)O(2), and partially by xylanase. We have isolated an interacting partner of OXI1, a Ser/Thr kinase (PTI1-2), which is downstream of OXI1. Its sequence closely resembles the tomato Pti kinase, which has been implicated in the hypersensitive response, a localized programmed cell death that occurs at the site of pathogen infection. PTI1-2 is activated by the same stresses/elicitors as OXI1 and additionally flagellin. We have used RNA interference to knock out the expression of PDK1 and OXI1 and to study the effects on PTI1-2 activity. We show that specific lipid signaling pathways converge on PTI1-2 via the PDK1-OXI1 axis, whereas H(2)O(2) and flagellin signals to OXI1-PTI1-2 via a PDK1-independent pathway. PTI1-2 represents a new downstream component that integrates diverse lipid and reactive oxygen stress signals and functions closely with OXI1.
Anthony
Richard G
RG
School of Biological Sciences, Royal Holloway, University of London, Egham Hill, Egham, Surrey TW20 0EX, United Kingdom. r.g.anthony@rhul.ac.uk
Khan
Safina
S
Costa
Joana
J
Pais
Maria S
MS
Bögre
László
L
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D008954:Models, Biological; D008969:Molecular Sequence Data; D018384:Oxidative Stress; D010712:Phosphatidic Acids / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques
D029681:Arabidopsis Proteins; D010712:Phosphatidic Acids; D010940:Plant Proteins; D064413:3-Phosphoinositide-Dependent Protein Kinases; C482589:OXI1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases