Abstract:

Background & Aims: Desiccation tolerance (DT) is a remarkable survival strategy in plants, allowing them to withstand extreme water deficits and resume full metabolic function upon rehydration. While this trait is crucial for life in arid environments, its underlying mechanisms vary significantly across the plant kingdom. As pioneers of terrestrial ecosystems, bryophytes exhibit exceptional DT, with the desert moss Syntrichia caninervis representing a model organism for its extraordinary resilience. Despite growing interest in its stress physiology, systematic syntheses addressing its integrated adaptive strategies across multiple biological levels remain limited. A comprehensive analysis of DT in S. caninervis is thus critical to unraveling its role in shaping plant evolution, optimizing survival in harsh climates, and providing novel genetic resources for crop improvement. 

Progress: This review presents a systematic elucidation of the multi-level adaptive strategies for desiccation tolerance in S. caninervis. Morphologically, features such as inward leaf curling, surface papillae, and hyaline awns constitute a first line of defense. Physiologically, the moss employs an efficient osmotic adjustment system, a robust antioxidant defense network, and mechanisms for protecting subcellular structures, which collectively enable the rapid recovery of photosynthesis. Multi-omics analyses have revealed a two-phase survival strategy: entering a quiescent state via cellular protection and metabolic depression during dehydration, followed by the rapid activation of cellular repair and metabolic recovery upon rehydration. The molecular basis of this tolerance is linked to the significant expansion and tandem duplication of key gene families, such as Late Embryogenesis Abundant (LEA) and Early Light-Inducible Proteins (ELIP), alongside synergistic regulation by diverse transcription factors. Furthermore, the establishment of an efficient genetic transformation system has validated the function of over 60 stress-responsive genes with proven potential for enhancing drought and salt tolerance in crops. 

Prospects: Current research on the DT mechanisms of S. caninervis is advancing rapidly, yet critical knowledge gaps persist in understanding its genetic architecture, signaling pathways, and evolutionary trajectories. Addressing these fundamental questions requires multidisciplinary approaches integrating genomics, proteomics, metabolomics, and developmental biology. This line of investigation holds significant implications for elucidating the evolutionary innovation of plant stress tolerance, identifying the drivers of adaptation to extreme environments, and deciphering the intricate regulatory networks governing cellular survival. Systematic exploration of S. caninervis will ultimately provide both a theoretical framework for plant adaptation and a valuable gene repository for breeding "climate-smart" drought-resistant crops.

Key words: desiccation tolerance, Syntrichia caninervis, molecular mechanism, physiological adaptation, genetic resources, crop drought breeding