Abstract
PSY1R is a leucine-rich repeat (LRR) receptor-like kinase (RLK) previously shown to act as receptor for the plant peptide hormone PSY1 (peptide containing sulfated tyrosine 1) and to regulate cell expansion. PSY1R phosphorylates and thereby regulates the activity of plasma membrane-localized H+-ATPases. While this mechanism has been studied in detail, little is known about how PSY1R itself is activated. Here we studied the activation mechanism of PSY1R. We show that full-length PSY1R interacts with members of the SERK co-receptor family in planta. We identified seven in vitro autophosphorylation sites on serine and threonine residues within the kinase domain of PSY1R using mass spectrometry. We furthermore show that PSY1R autophosphorylation occurs in trans and that the initial transphosphorylation takes place within the activation loop at residues Ser951, Thr959, and Thr963. While Thr959 and Thr963 are conserved among other related plant LRR RLKs, Ser951 is unique to PSY1R. Based on homology modeling we propose that phosphorylation of Ser951 stabilize the inactive conformation of PSY1R.
Highlights
As multicellular organisms, plants rely on a fine-tuned cell-to-cell communication system to coordinate growth responses
By homology modeling to known structures of BRI1 and SIRK1 we propose how these residues are involved in stabilization of the activation loop in the active and inactive state, respectively
Recombinant kPSY1R were incubated in an in vitro kinase assay in the absence or presence of ATP and phosphorylated amino acids were detected with phosphoamino acid-specific antibodies
Summary
Plants rely on a fine-tuned cell-to-cell communication system to coordinate growth responses. At the core of this system are members of the receptor-like kinase (RLK) superfamily. This massive family of plant proteins, which is implicated in both plant development (De Smet et al, 2009; Murphy et al, 2012) and plant innate immunity (Schwessinger and Ronald, 2012; Tang et al, 2017), maintains an appropriate balance between growth and defense. Plant RLKs belong to the RLK/Pelle class of protein kinases, which is composed of over 600 members in Arabidopsis (Gish and Clark, 2011), and are related to the mammalian Receptor Tyrosine Kinases (RTKs) (Shiu and Bleecker, 2001; Belkhadir et al, 2014). Plant peptide hormones, which are expressed as precursor peptides (pre-pro-peptides) and undergo
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