Abstract
Karrikins are smoke-derived compounds presumed to mimic endogenous signalling molecules (KAI2-ligand, KL), whose signalling pathway is closely related to that of strigolactones (SLs), important regulators of plant development. Both karrikins/KLs and SLs are perceived by closely related α/β hydrolase receptors (KAI2 and D14 respectively), and signalling through both receptors requires the F-box protein MAX2. Furthermore, both pathways trigger proteasome-mediated degradation of related SMAX1-LIKE (SMXL) proteins, to influence development. It has previously been suggested in multiple studies that SLs are important regulators of root and root hair development in Arabidopsis, but these conclusions are based on phenotypes observed in the non-specific max2 mutants and by use of racemic-GR24, a mixture of stereoisomers that activates both D14 and KAI2 signalling pathways. Here, we demonstrate that the majority of the effects on Arabidopsis root development previously attributed to SL signalling are actually mediated by the KAI2 signalling pathway. Using mutants defective in SL or KL synthesis and/or perception, we show that KAI2-mediated signalling alone regulates root hair density and root hair length as well as root skewing, straightness and diameter, while both KAI2 and D14 pathways regulate lateral root density and epidermal cell length. We test the key hypothesis that KAI2 signals by a non-canonical receptor-target mechanism in the context of root development. Our results provide no evidence for this, and we instead show that all effects of KAI2 in the root can be explained by canonical SMAX1/SMXL2 activity. However, we do find evidence for non-canonical GR24 ligand-receptor interactions in D14/KAI2-mediated root hair development. Overall, our results demonstrate that the KAI2 signalling pathway is an important new regulator of root hair and root development in Arabidopsis and lay an important basis for research into a molecular understanding of how very similar and partially overlapping hormone signalling pathways regulate different phenotypic outputs.
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Claims 7
Claim · model-written summary
Most previously attributed strigolactone effects on Arabidopsis root development were mediated by KAI2 signaling.
- Taxon
- Arabidopsis
Arabidopsise0 - Gene
- KAI2e0
- Outcome
- root developmente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the majority of the effects on Arabidopsis root development previously attributed to SL signalling are actually mediated by the KAI2 signalling pathway”
Claim · model-written summary
KAI2 signaling alone regulates root hair density and length in Arabidopsis.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- KAI2e0
- Outcome
- root hair density and root hair lengthe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“KAI2-mediated signalling alone regulates root hair density and root hair length as well as root skewing, straightness and diameter”
t0“Arabidopsis”
Claim · model-written summary
KAI2 signaling alone regulates root skewing, straightness and diameter in Arabidopsis.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- KAI2e0
- Outcome
- root skewing, straightness and diametere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“KAI2-mediated signalling alone regulates root hair density and root hair length as well as root skewing, straightness and diameter”
t0“Arabidopsis”
Claim · model-written summary
Both KAI2 and D14 pathways regulate lateral root density and epidermal cell length.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- KAI2 and D14e0
- Outcome
- lateral root density and epidermal cell lengthe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“both KAI2 and D14 pathways regulate lateral root density and epidermal cell length”
t0“Arabidopsis”
Claim · model-written summary
No evidence supported a non-canonical KAI2 receptor-target mechanism in root development.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- KAI2e0
- Outcome
- no evidence for thise0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We test the key hypothesis that KAI2 signals by a non-canonical receptor-target mechanism in the context of root development. Our results provide no evidence for this”
t0“Arabidopsis”
Claim · model-written summary
Canonical SMAX1/SMXL2 activity explained all KAI2 effects in the root.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- SMAX1/SMXL2e0
- Outcome
- effects of KAI2 in the roote0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“all effects of KAI2 in the root can be explained by canonical SMAX1/SMXL2 activity”
t0“Arabidopsis”
Claim · model-written summary
The study found evidence for non-canonical GR24 ligand-receptor interactions in D14/KAI2-mediated root hair development.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- root haire0
- Gene
- D14/KAI2e0
- Outcome
- non-canonical GR24 ligand-receptor interactionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“evidence for non-canonical GR24 ligand-receptor interactions in D14/KAI2-mediated root hair development”
t0“Arabidopsis”