Journal Article

Mechanistic insight into a peptide hormone signaling complex mediating floral organ abscission

Hothorn, Ludwig A, Brandt, Benjamin, Wildhagen, Mari, Hohmann, Ulrich, Butenko, Melinka A, Santiago, Julia, Hothorn, Michael

2016

Overview

Plants constantly renew during their life cycle and thus require to shed senescent and damaged organs. Floral abscission is controlled by the leucine-rich repeat receptor kinase (LRR-RK) HAESA and the peptide hormone IDA. It is unknown how expression of IDA in the abscission zone leads to HAESA activation. Here we show that IDA is sensed directly by the HAESA ectodomain. Crystal structures of HAESA in complex with IDA reveal a hormone binding pocket that accommodates an active dodecamer peptide. A central hydroxyproline residue anchors IDA to the receptor. The HAESA co-receptor SERK1, a positive regulator of the floral abscission pathway, allows for high-affinity sensing of the peptide hormone by binding to an Arg-His-Asn motif in IDA. This sequence pattern is conserved among diverse plant peptides, suggesting that plant peptide hormone receptors may share a common ligand binding mode and activation mechanism. Plants can shed their leaves, flowers or other organs when they no longer need them. But how does a leaf or a flower know when to let go? A receptor protein called HAESA is found on the surface of the cells that surround a future break point on the plant. When its time to shed an organ, a hormone called IDA instructs HAESA to trigger the shedding process. However, the molecular details of how IDA triggers organ shedding are not clear. The shedding of floral organs (or leaves) can be easily studied in a model plant called Arabidopsis. Santiago et al. used protein biochemistry, structural biology and genetics to uncover how the IDA hormone activates HAESA. The experiments show that IDA binds directly to a canyon shaped pocket in HAESA that extends out from the surface of the cell. IDA binding to HAESA allows another receptor protein called SERK1 to bind to HAESA, which results in the release of signals inside the cell that trigger the shedding of organs. The next step following on from this work is to understand what signals are produced when IDA activates HAESA. Another challenge will be to find out where IDA is produced in the plant and what causes it to accumulate in specific places in preparation for organ shedding.

• Publisher: eLife Sciences Publications Ltd,eLife Sciences Publications, Ltd
• Subject: Abscission / Arabidopsis - physiology / Arabidopsis Proteins - biosynthesis / Arabidopsis Proteins - chemistry / Arabidopsis Proteins - metabolism / Arabidopsis thaliana / Binding Sites / Biophysics and Structural Biology / Conserved sequence / Crystallography, X-Ray / floral abscission / Flowers - physiology / Gene expression / Gene Expression Regulation, Plant / Hydroxyproline / Kinases / Leucine / Life cycles / membrane signaling / peptide hormone / Peptides / Plant Biology / plant development / Protein Binding / protein complexes / Protein Conformation / Protein Kinases - metabolism / Protein-Serine-Threonine Kinases - biosynthesis / Protein-Serine-Threonine Kinases - chemistry / Proteins / receptor kinase / Signal Transduction