Organisms depend on water for survival. Understanding desiccation tolerance mechanisms is critical for the reproduction of grass bioenergy crops, whose pollen grains are dispersed by air and able to survive only from a few minutes to few hours once shed from the anthers and exposed to the environment. Most mature pollen grains from flowering plants become metabolically quiescent and highly desiccated (15%-30% water content) once outside the anthers, with the striking exception of pollen grains from most grasses (35%-60% water content), including all grass bioenergy crops such as sorghum, miscanthus, and switchgrass (Panicum virgatum). We propose to analyze mature pollen grains of Pennisetum typhoides and Arabidopsis thaliana (desiccation tolerant) and energy sorghum (desiccation-sensitive) by cryo-electron microscopy imaging approaches to reveal the cellular and molecular strategies that allow them to survive desiccation. Specifically, we aim to: (1) Analyze the cellular rearrangements associated with desiccation tolerance in pollen grains subjected to different relative humidities by cryo-block face surface imaging. (2) Dissect the molecular structural features of ribosomes, cellular membranes, and major organelles associated to desiccation tolerance by cryo-lamella preparation and cryo-electron tomography. Understanding the cellular and molecular traits that underlying pollen desiccation tolerance will support efforts to engineer bioenergy grass crops with higher reproductive capacity in a warming planet. This project also aligns with the EMSL goal of understanding structure-function relationship at the molecular and cellular level to elucidate biological and cellular activities relevant to bioenergy crop production.