*Role of MS Channels in Pollen Development

Ec-MscS is a non-selective mechanosensitive ion channel that is gated directly through tension in the membrane, and serves as an osmotic release valve during hypoosmotic swelling. Thirty years of site-directed mutagenesis, in vivo physiology, crystallography and biophysical modeling experiments on Ec-MscS provide a strong foundation for investigations into MscS homologs, which are found in all three kingdoms of life. We recently discovered a related, but distinct, role for MSL proteins in pollen—the male gamete of plants. During fertilzation, pollen grains must undergo dramatic changes in cellular water potential in order to successfully deliver the male germline to female gametes. 

We used molecular genetics, single channel patch-clamp electrophysiology, live imaging, and novel in vitro assays for pollen function to identify and characterize MscS-Like (MSL)8, a pollen-specific, membrane tension-gated ion channel required for pollen to survive the hypoosmotic shock of rehydration and for full male fertility. MSL8 negatively regulates pollen germination, but is required for cellular integrity during germination and tube growth. Thus, a plant homolog of the bacterial mechanosensitive ion channel MscS is required to respond to multiple osmotic challenges during pollen hydration and germination. These data further suggest that homologs of bacterial MscS have been repurposed in eukaryotes to sense and respond to mechanical stimuli in a variety of developmental and environmental contexts.

  • E. S. Hamilton, G. S. Jensen, G. Maksaev, Andrew Katims, Ashley Sherp and E. S. Haswell. (2015). Mechanosensitive Ion Channel MSL8 Regulates Osmotic Forces During Pollen Hydration and Germination. Science 350:438-441.

  • Also see our YouTube video animating the results in the Science paper!

Next, we used electrophysiology, in vitro assays, and genetic transmission studies to show that two MSL8 channel variants with reduced conductance and/or tension sensitivity do not rescue the phenotypes of the msl8 null mutant. These results provide evidence that MSL8 acts directly as a mechanically gated osmotic conduit in pollen membranes, and establish MSL8 as a pollen mechanoreceptor.

  • E. S. Hamilton and E. S. Haswell. (2017). The Tension-sensitive Ion Transport Activity of MSL8 is Critical for its Function in Pollen Hydration and Germination. Plant Cell & Physiology 58: 1222-1237

MSL8 may serve as an osmotic safety valve in pollen


Overview of Pollen Hydration and Germination