With intensifying global warming and climate change, drought has become a major threat to global agriculture, impacting crop yields and food security. To survive such adverse events, plants have evolved several strategies. One such strategy to counteract water scarcity is 'stomatal closure,' where stomata—the tiny pores on leaf surfaces responsible for gaseous exchange—close to limit water loss. This process is regulated by the plant hormone abscisic acid (ABA), which plays a crucial role in the plant's internal stress-response mechanisms.
While the role of ABA in drought response is well-established, researchers have now identified a surprising contributor to this process: myosin XI, a motor protein traditionally known for transporting cellular components. To explore this, a team of researchers led by Professor Motoki Tominaga from Waseda University, Japan, conducted a study to determine whether myosin XI actively contributes to drought response in plants and to uncover the processes involved. "Although previous studies have suggested a potential involvement of myosin XI in drought stress responses, the underlying mechanisms have remained unclear," shares Tominaga. The findings of this research were published in Volume 44 of Plant Cell Reports on June 19, 2025. The study was co-authored by Graduate Student Haiyang Liu, also from Waseda University.
Researchers used Arabidopsis thaliana as a model to investigate the role of myosin XI in drought response. They used genetically modified plants lacking one, two (2ko), or all three (3ko), major myosin XI genes. These were then compared to wild-type plants across several tests, including drought survival assays, water loss measurements, stomatal aperture analysis, and ABA sensitivity. They also measured reactive oxygen species (ROS) production, visualized microtubules with fluorescent markers, and tracked expression of ABA-responsive genes via qRT-PCR. This comprehensive approach allowed them to assess the functional contribution of myosin XI to drought tolerance and ABA signaling in plants.
The results were striking. Plants lacking myosin XI, especially the 2ko and 3ko mutants, showed a higher rate of water loss, impaired stomatal closure, and lower survival under drought. They were also less responsive to ABA, as seen in higher germination rates and reduced inhibition of root growth under hormone treatment. At the cellular level, these mutants exhibited reduced ROS production as well as disrupted microtubule remodeling, both of which are essential for ABA-induced stomatal closure. Key stress-related genes also showed decreased expression, indicating that myosin XI plays a regulatory role in ABA signaling.
