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Structural basis for recognition of RALF peptides by LRX proteins during pollen tube growth


Moussu, Steven; Broyart, Caroline; Santos-Fernandez, Gorka; Augustin, Sebastian; Wehrle, Sarah; Grossniklaus, Ueli; Santiago, Julia (2019). Structural basis for recognition of RALF peptides by LRX proteins during pollen tube growth. bioRxiv 695874, University of Zurich.

Abstract

Plant reproduction relies on the highly regulated growth of the pollen tube for proper sperm delivery. This process is controlled by secreted RALF signaling peptides, which have been previously shown to be perceived by <jats:italic>Cr</jats:italic>RLK1Ls membrane receptor-kinases and leucine-rich (LRR) extensin proteins (LRXs). Here we demonstrate that RALF peptides are active as folded, disulfide bond-stabilized proteins, which can bind to the LRR domain of LRX proteins with nanomolar affinity. Crystal structures of the LRX-RALF signaling complexes reveal LRX proteins as constitutive dimers. The N-terminal LRR domain containing the RALF binding site is tightly linked to the extensin domain via a cysteine-rich tail. Our biochemical and structural work reveals a complex signaling network by which RALF ligands may instruct different signaling proteins – here <jats:italic>Cr</jats:italic>RLK1Ls and LRXs – through structurally different binding modes to orchestrate cell wall remodeling in rapidly growing pollen tubes.<jats:sec>SignificancePlant reproduction relies on proper pollen tube growth to reach the female tissue and release the sperm cells. This process is highly regulated by a family of secreted signaling peptides that are recognized by cell-wall monitoring proteins to enable plant fertilization. Here, we report the crystal structure of the LRX-RALF cell-wall complex and we demonstrate that RALF peptides are active as folded proteins. RALFs are autocrine signaling proteins able to instruct LRX cell-wall modules and <jats:italic>Cr</jats:italic>RKL1L receptors, through structurally different binding modes to coordinate pollen tube integrity.</jats:sec>

Abstract

Plant reproduction relies on the highly regulated growth of the pollen tube for proper sperm delivery. This process is controlled by secreted RALF signaling peptides, which have been previously shown to be perceived by <jats:italic>Cr</jats:italic>RLK1Ls membrane receptor-kinases and leucine-rich (LRR) extensin proteins (LRXs). Here we demonstrate that RALF peptides are active as folded, disulfide bond-stabilized proteins, which can bind to the LRR domain of LRX proteins with nanomolar affinity. Crystal structures of the LRX-RALF signaling complexes reveal LRX proteins as constitutive dimers. The N-terminal LRR domain containing the RALF binding site is tightly linked to the extensin domain via a cysteine-rich tail. Our biochemical and structural work reveals a complex signaling network by which RALF ligands may instruct different signaling proteins – here <jats:italic>Cr</jats:italic>RLK1Ls and LRXs – through structurally different binding modes to orchestrate cell wall remodeling in rapidly growing pollen tubes.<jats:sec>SignificancePlant reproduction relies on proper pollen tube growth to reach the female tissue and release the sperm cells. This process is highly regulated by a family of secreted signaling peptides that are recognized by cell-wall monitoring proteins to enable plant fertilization. Here, we report the crystal structure of the LRX-RALF cell-wall complex and we demonstrate that RALF peptides are active as folded proteins. RALFs are autocrine signaling proteins able to instruct LRX cell-wall modules and <jats:italic>Cr</jats:italic>RKL1L receptors, through structurally different binding modes to coordinate pollen tube integrity.</jats:sec>

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Item Type:Working Paper
Communities & Collections:07 Faculty of Science > Department of Plant and Microbial Biology
07 Faculty of Science > Zurich-Basel Plant Science Center
Dewey Decimal Classification:580 Plants (Botany)
Language:English
Date:8 July 2019
Deposited On:05 Feb 2020 16:28
Last Modified:29 Jul 2020 13:22
Series Name:bioRxiv
ISSN:2164-7844
OA Status:Green
Publisher DOI:https://doi.org/10.1101/695874

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