In both plants and animals, a family of proteins named receptor kinases are largely responsible for sensing the environment. Plants use receptor kinases as ‘molecular antennas’ to recognize chemical signals, such as growth hormones or portions of proteins from pathogens, from outside the cell and initiate responses to this signal inside the cell. The model plant Arabidopsis thaliana contains over 600 of these receptor kinases – ten times more than are found in humans – and they are critical for plant growth, development, immunity, and stress responses. Despite this importance, the function of only a handful of these proteins is known; even less is known about how these receptors interact with each to coordinate responses to often conflicting signals.
The Belkhadir lab implemented a high-throughput assay to test interactions between the receptors in a pairwise manner. They cloned and expressed more than 400 extracellular domains of leucine-rich repeat receptor kinases (LRR-RKs) and performed 40,000 interaction tests, testing whether each protein interacted with any of the others, and produced an interaction map displaying how the receptor kinases interact with one another. They found that LRR-RKs that have small extracellular domains interact with other LRR-RKs more often than their counterparts with large domains, suggesting that these small LRR-RKs have evolved to coordinate the actions of the rest of the receptors. Second, they identified several unknown LRR-RKs that appear to be critical for network integrity.
The most important of these new LRR-RKs was named APEX, and its removal led to significant changes in plant developmental and immune responses controlled by two other LRR-RKs that do not interact with APEX and are several network steps away. Therefore, the receptor network map can be mined to find important receptors that affect multiple, diverse plant response pathways.
Elwira Smakowska-Luzan, et al. An extracellular network of Arabidopsis leucine-rich repeat receptor kinases.
Nature, 10 January 2018