SPY Interacts With Tubulin and Regulates Abscisic Acid-Induced Stomatal Closure in Arabidopsis

Sugars are important both as an energy source and a signaling cue. In Arabidopsis thaliana, SPINDLY (SPY) is the bona fide O-fucosylation transferase that links sugar with various plant growth and development processes. Previously, spy was shown to display a strong salt and drought tolerance phenotype. Herein we confirmed the phenotype and further studied its mechanism. We found that abscisic acid (ABA) elevated SPY expression in guard cells, and SPY is involved in ABA-induced stomatal closure. We show that SPY regulates the rearrangement of the microtubule cytoskeleton in guard cells. Moreover, ABA-induced microtubule reorganization is enhanced in spy mutants. Mechanistically, SPY interacts with α-tubulin1 (TUA1) in both yeast-two hybrid, bimolecular fluorescence complementation and split luciferase complementation imaging assays, indicating that TUA1 may be O-fucosylated by SPY. Our work is in line with the notion that SPY has many substrates involved in diverse processes in plants, and also unearths a key mechanism how glycosylation regulates the stomata movement via the microtubule cytoskeleton.