This paper reviews this state of the art in measuring plant signaling, using principles and tools borrowed from and inspired by engineering, as well as efforts to use this knowledge to enable rapid, rational re-engineering of plant development.
Sensitive, genetically encoded reporters (biosensors), in combination with emerging single-cell transcriptomics approaches, are providing increasingly detailed molecular descriptions of cells undergoing developmental transitions
Salicylic acid (SA) is a plant hormone that is critical for resistance to pathogens. The NPR proteins have previously been identified as SA receptors although how they perceive SA and coordinate hormonal signalling remain unknown. Here we report the mapping of the SA-binding core of Arabidopsis thaliana NPR4 and its ligand-bound crystal structure. The SA-binding core domain of NPR4 refolded with SA adopts an α-helical fold that completely buries SA in its hydrophobic core. The lack of a ligand-entry pathway suggests that SA binding involves a major conformational remodelling of the SA-binding core of NPR4, which we validated using hydrogen–deuterium-exchange mass spectrometry analysis of the full-length protein and through SA-induced disruption of interactions between NPR1 and NPR4. We show that, despite the two proteins sharing nearly identical hormone-binding residues, NPR1 displays minimal SA-binding activity compared to NPR4. We further identify two surface residues of the SA-binding core, the mutation of which can alter the SA-binding ability of NPR4 and its interaction with NPR1. We also demonstrate that expressing a variant of NPR4 that is hypersensitive to SA could enhance SA-mediated basal immunity without compromising effector-triggered immunity, because the ability of this variant to re-associate with NPR1 at high levels of SA remains intact. By revealing the structural mechanisms of SA perception by NPR proteins, our work paves the way for future investigation of the specific roles of these proteins in SA signalling and their potential for engineering plant immunity.
Together, our data indicate that light exerts opposite regulation of LAZY4 expression in shoots and roots by mediating the protein levels of PIFs and HY5, respectively, to inhibit the negative gravitropism of shoots and promote positive gravitropism of roots in Arabidopsis.
In hypocotyls, light promotes degradation of PIFs to reduce LAZY4 expression, which inhibits the negative gravitropism of hypocotyls.
A systems-level map of the Arabidopsis hormone signalling network, comprising more than 2,000 binary protein–protein interactions, reveals hundreds of interpathway contact points, many of which mediate crosstalk between different hormone pathways.