An Original Study of Desiccation Tolerance Mechanisms in Poikilohydric Vascular Plants of the Nigerian Inselbergs: Integrating Ultrastructure, Proteomics, and Gene Expression

Poikilohydric vascular plants that tolerate complete desiccation are rare globally but are disproportionately represented on Nigerian granite inselbergs, which serve as islands of extraordinary botanical diversity, yet the integrated mechanisms conferring desiccation tolerance at the cellular, proteomic, and transcriptomic levels in these plants have not been studied, representing a significant gap in plant stress biology. This study presents an original integrated investigation of desiccation tolerance mechanisms in three poikilohydric vascular plants endemic or characteristic of Nigerian inselbergs: Myrothamnus flabellifolius, Vellozia schnizleiniana, and Coleochloa setifera, collected from inselberg sites in Kogi, Kwara, and Plateau States. Plants were subjected to controlled desiccation cycles (0, 25, 50, 75, and 100% relative water content loss) and rehydration, with sampling at each desiccation stage. Ultrastructural changes were characterised by transmission electron microscopy. Proteome responses were profiled by isobaric tag for relative and absolute quantification (iTRAQ) quantitative proteomics using an Orbitrap mass spectrometer. Transcriptome responses were characterised by de novo RNA-Seq assembly and differential expression analysis. An original cell wall pliability assay was developed to quantify cell wall mechanical deformation during desiccation. Results revealed that all three species maintained vacuolar integrity until below 30% relative water content, facilitated by cell wall folding rather than collapse, with the degree of wall pliability correlating with desiccation tolerance depth. Proteomics identified 318 uniquely abundant proteins in the most desiccation-tolerant species, including 8 previously undescribed group 3 late embryogenesis abundant proteins and 4 novel antioxidant enzymes. RNA-Seq confirmed upregulation of autophagy and protein repair pathways unique to complete desiccation events. An original Integrated Desiccation Tolerance Mechanistic Model is proposed, unifying cell wall, proteomic, and transcriptomic responses into a coherent sequence of cellular protection events. The study makes an original contribution to the global understanding of vascular plant desiccation tolerance mechanisms.

Keywords: desiccation tolerance, poikilohydric plants, inselbergs, proteomics, transcriptomics