Cellular membranes act as signaling platforms and control solute transport. Membrane receptors,
transporters, and enzymes communicate with intracellular processes through protein-protein
interactions. Using a split-ubiquitin yeast two-hybrid screen that covers a test-space of 6.4 × 106
pairs, we identified 12,102 membrane/signaling protein interactions from Arabidopsis. Besides
confirmation of expected interactions such as heterotrimeric G protein subunit interactions and
aquaporin oligomerization, >99% of the interactions were previously unknown. Interactions were
confirmed at a rate of 32% in orthogonal in planta split–green fluorescent protein interaction assays,
which was statistically indistinguishable from the confirmation rate for known interactions collected
from literature (38%). Regulatory associations in membrane protein trafficking, turnover, and
phosphorylation include regulation of potassium channel activity through abscisic acid signaling,
transporter activity by a WNK kinase, and a brassinolide receptor kinase by trafficking-related proteins.
These examples underscore the utility of the membrane/signaling protein interaction network for gene
discovery and hypothesis generation in plants and other organisms.