Andersen, C. G. | Search bioRxiv

bioRxiv2024

Two residues reprogram immunity receptor kinases to signal in nitrogen-fixing symbiosis

Receptor signalling determines cellular responses and is crucial for defining specific biological outcomes. In legume root cells, highly similar and structurally conserved chitin and Nod factor receptor kinases activate immune or symbiotic pathways, respectively, upon perception of chitinous ligands. Here, we show that specific amino acid residues in the intracellular part of the Nod factor receptor NFR1 determine signalling specificity and enable the distinction between immune and symbiotic responses. Functional investigation of CERK6, NFR1 and receptor variants hereof revealed a conserved motif that we term Symbiosis Determinant 1 in the juxtamembrane region of the kinase domain that is key for symbiotic signalling. We demonstrate that two residues in Symbiosis Determinant 1 are indispensable hallmarks for NFR1-type receptors and are sufficient to convert Lotus CERK6 and barley RLK4 kinase outputs to enable symbiotic signalling in Lotus japonicus.

plant biology↗

bioRxiv2024

Comparative analysis of STP6 and STP10 rationalizes molecular selectivity in Sugar Transport Proteins

The distribution of sugars is crucial for plant energy, signaling, and defense mechanisms. Sugar Transport Proteins (STPs) are Sugar Porters that mediate proton-driven cellular uptake of glucose. Some STPs also transport fructose, while others remain highly selective for only glucose. What determines this selectivity, allowing STPs to distinguish between compounds with highly similar chemical composition, remains unknown. Here, we present the structure of Arabidopsis thaliana STP6 in an inward occluded conformational state with glucose bound and demonstrate its role as both a glucose and fructose transporter. We perform a comparative analysis of STP6 with the glucose-selective STP10 using in-vivo and in-vitro systems, demonstrating how different experimental setups strongly influence kinetic transport properties. We analyze the properties of the monosaccharide binding site and show that the position of a single methyl group in the binding site is sufficient to shuffle glucose and fructose specificity, providing detailed insights into the fine-tuned dynamics of affinity-induced specificity for sugar uptake. Altogether these findings enhance our understanding of sugar selectivity in STPs and more broadly Sugar Porter proteins. SIGNIFICANCE STATEMENTUnderstanding the mechanisms of sugar transport in plants is essential for advancing agricultural practices and enhancing plant resilience. This study reveals the structural basis of sugar selectivity in Sugar Transport Proteins of Arabidopsis thaliana. By comparing the dual-specific STP6, transporting both glucose and fructose with the glucose-selective STP10 across multiple experimental setups, we show that difference as subtle as the position of a single methyl group in the binding site can control sugar specificity. These findings enhance our understanding of sugar selectivity by Sugar Transport Proteins and more broadly Sugar Porter proteins and lay the groundwork for engineering crops with improved energy efficiency and pathogen resistance.

biochemistry↗