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Evolution of strigolactone receptors by gradual neo-functionalization of KAI2 paralogues
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- Author(s) / Creator(s)
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Background: Strigolactones (SLs) are a class of plant hormones that control many aspects of plant growth. The SL
signalling mechanism is homologous to that of karrikins (KARs), smoke-derived compounds that stimulate seed
germination. In angiosperms, the SL receptor is an α/β-hydrolase known as DWARF14 (D14); its close homologue,
KARRIKIN INSENSITIVE2 (KAI2), functions as a KAR receptor and likely recognizes an uncharacterized, endogenous
signal (‘KL’). Previous phylogenetic analyses have suggested that the KAI2 lineage is ancestral in land plants, and
that canonical D14-type SL receptors only arose in seed plants; this is paradoxical, however, as non-vascular plants
synthesize and respond to SLs.
Results: We have used a combination of phylogenetic and structural approaches to re-assess the evolution of the
D14/KAI2 family in land plants. We analysed 339 members of the D14/KAI2 family from land plants and charophyte
algae. Our phylogenetic analyses show that the divergence between the eu-KAI2 lineage and the DDK (D14/DLK2/
KAI2) lineage that includes D14 occurred very early in land plant evolution. We show that eu-KAI2 proteins are
highly conserved, and have unique features not found in DDK proteins. Conversely, we show that DDK proteins
show considerable sequence and structural variation to each other, and lack clearly definable characteristics. We use
homology modelling to show that the earliest members of the DDK lineage structurally resemble KAI2 and that SL
receptors in non-seed plants likely do not have D14-like structure. We also show that certain groups of DDK
proteins lack the otherwise conserved MORE AXILLARY GROWTH2 (MAX2) interface, and may thus function
independently of MAX2, which we show is highly conserved throughout land plant evolution.
Conclusions: Our results suggest that D14-like structure is not required for SL perception, and that SL
perception has relatively relaxed structural requirements compared to KAI2-mediated signalling. We suggest
that SL perception gradually evolved by neo-functionalization within the DDK lineage, and that the transition
from KAI2-like to D14-like protein may have been driven by interactions with protein partners, rather than
being required for SL perception per se. -
- Date created
- 2017-06-29
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- Subjects / Keywords
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- Type of Item
- Article (Published)
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- License
- Attribution 4.0 International