Wax bloom dynamics on Sorghum bicolor under different environmental stresses reveal signaling modules associated with wax production

Abstract

Epicuticular wax blooms are associated with improved drought resistance in many species, including Sorghum bicolor. While the role of wax in drought resistance is well known, we report new insights into how light and drought dynamically influence wax production. We investigated how wax quantity and composition are modulated over time and in response to different environmental stressors, as well as the molecular and genetic mechanisms involved in such. Gas chromatography-mass spectrometry and photographic results showed that sorghum leaf sheath wax load and composition were altered in mature plants grown under drought and simulated shade, though this phenomenon appears to vary by sorghum cultivar. We combined an in vitro wax induction protocol with GC-MS and RNA-seq measurements to identify a draft signaling pathway for wax bloom induction in sorghum. We also explored the potential of spectrophotometry to aid in monitoring wax bloom dynamics. Spec-trophotometric analysis showed primary differences in reflectance between bloom-rich and bloomless tissue surfaces in the 230-500nm range of the spectrum, corresponding to the blue color channel of photographic data. Our smartphone-based system detected significant differences in wax production between control and shade treatment groups, demonstrating its potential for candidate screening. Overall, our data suggest that wax extrusion can be rapidly modulated in response to light, occurring within days compared to the months required for the changes observed under greenhouse drought/simulated shade conditions. These results highlight the dynamic nature of wax modulation in response to varying environmental stimuli, especially light and water availability. Significance StatementAgricultural crops require significant freshwater for irrigation, making food security vulnerable to drought. Epicuticular wax blooms are associated with drought tolerance in many plants, including Sorghum bicolor. We investigated how environmental factors like light and drought influence wax production in sorghum. Wax production, composition, and gene expression were compared between sorghum exposed to different environmental stressors, reavealing dynamic modulation of wax production in response to environmental stress as well as signaling genes potentially involved in regulating wax production. These findings broaden our understanding of wax-related drought tolerance mechanisms, providing a foundation for future efforts to enginner crops with improved climate resilience.