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Review
. 2012;8(11):e1003026.
doi: 10.1371/journal.ppat.1003026. Epub 2012 Nov 29.

The role of auxin-cytokinin antagonism in plant-pathogen interactions

Muhammad Naseem  1 , Thomas Dandekar
Affiliations
Review

The role of auxin-cytokinin antagonism in plant-pathogen interactions

Muhammad Naseem et al. PLoS Pathog. 2012.
No abstract available

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Auxin-cytokinin interaction in plant immunity.
Pseudomonas syringae pv. tomato DC3000 (Pto) resides in the apoplast of adjacent Arabidopsis cells . Besides other substances, the apoplast also contains various sugars, ions, and free hormones cytokinin and auxin (green and light blue chemical structures). Pto injects effectors via TTSS (Type III secretion system) into the plant cell . This causes higher auxin accumulation in the cytoplasm. Auxin also diffuses directly from the apoplast or is taken into the cytoplasm by AUX1 (auxin influx transporter) . Excess of auxin releases ARF (auxin response factor) from AUX/IAA (auxin repressor) and keeps auxin responses derepressed . Auxin crosstalk enhances synergistically the JA pathway (gray boxes) at the level of JA biosynthesis and downstream signaling to enhance PDF1.2 (marker for JA/ET pathway [13]). Auxin represses the SA pathway (white boxes) to cause susceptibility of Arabidopsis against the infection of Pto . During the course of infection, Pto decreases the level of cytokinin (green structures in apoplast) . Cytokinins are perceived by AHKs (Arabidopsis histidine kinase) and transduced by a two-component phosphorelay system (yellow boxes); the signal of phosphorylation is transduced from receptor to AHPs (Arabidopsis histidine phosphotransfer protein) in the cytoplasm . Subsequently, type-B ARRs (positive regulator of cytokinin response) are phosphorylated, and they in turn activate the expression of type-A ARRs (repressor of cytokinin signaling) . Cytokinin activates the SA pathway (white boxes) at the level of TGA3 via type-B ARR2 in an NPR1-dependent manner . In a negative feedback loop, type-A ARRs also inhibit cytokinin responses . Cytokinin also inhibits auxin transport by keeping PIN1 auxin efflux transporters arrested and thus causes imbalance in auxin flux and distribution inside the tissue . Auxin and cytokinin, besides mutual inhibition, contribute differentially to the SA-JA/ET backbone of plant defense against pathogens .
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Grants and funding

We thank the German Research Society (DFG), grant Da 208/10-2, for support. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.