Abstract
Transportation of the immobile sperms directed by pollen tubes to the ovule-enclosed female gametophytes is important for plant sexual reproduction. The defensin-like (DEFL) cysteine-rich peptides (CRPs) LUREs play an essential role in pollen tube attraction to the ovule, though their receptors still remain controversial. Here we provide several lines of biochemical evidence showing that the extracellular domain of the leucine-rich repeat receptor kinase (LRR-RK) PRK6 from Arabidopsis thaliana directly interacts with AtLURE1 peptides. Structural study reveals that a C-terminal loop of the LRR domain (AtPRK6LRR) is responsible for recognition of AtLURE1.2, mediated by a set of residues largely conserved among PRK6 homologs from Arabidopsis lyrata and Capsella rubella, supported by in vitro mutagenesis and semi-in-vivo pollen tube growth assays. Our study provides evidence showing that PRK6 functions as a receptor of the LURE peptides in A. thaliana and reveals a unique ligand recognition mechanism of LRR-RKs.
Highlights
Transportation of the immobile sperms directed by pollen tubes to the ovule-enclosed female gametophytes is important for plant sexual reproduction
To identify receptor kinases (RKs) that can interact with AtLURE1 in vitro, we purified the proteins of the mature form of AtLURE1.2, the extracellular LRR domains of several AtPRK members and MIK1, 2 with a His-tag fused at their C-termini from insect cells
In the current study, we present biochemical, structural and functional evidence showing that AtPRK6 functioned as a receptor of AtLURE1, strongly supporting previous genetic data[20]
Summary
Transportation of the immobile sperms directed by pollen tubes to the ovule-enclosed female gametophytes is important for plant sexual reproduction. The defensin-like (DEFL) cysteinerich peptides (CRPs) LUREs play an essential role in pollen tube attraction to the ovule, though their receptors still remain controversial. We provide several lines of biochemical evidence showing that the extracellular domain of the leucine-rich repeat receptor kinase (LRR-RK) PRK6 from Arabidopsis thaliana directly interacts with AtLURE1 peptides. Our study provides evidence showing that PRK6 functions as a receptor of the LURE peptides in A. thaliana and reveals a unique ligand recognition mechanism of LRR-RKs. The final step of the guidance is micropylar pollen tube guidance in which a functional female gametophyte plays an essential role in pollen tube attraction to the ovule. Orthologs of LURE1 in Torenia concolor (TcCRP1)[15] and A. thaliana (AtLURE1)[9] were recently shown as key attractant molecules, indicating a significant role played by these secreted proteins in pollen tube guidance. No atoms Protein Ligand/ion Water B-factors Protein Ligand/ion Water R.m.s deviations Bond lengths (Å) Bond angles (°)
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