The architecture of resilience: a genome assembly of Myrothamnus flabellifolia sheds light on desiccation tolerance and sex determination

Abstract

Myrothamnus flabellifolia is a dioecious resurrection plant endemic to southern Africa that has become an important model for desiccation tolerance. Here, we present a chromosome-level, haplotype-resolved reference genome for M. flabellifolia alongside transcriptomic profiling across a natural dehydration-rehydration cycle. The 1.28 Gb genome exhibits unusually consistent chromatin architecture with putative holocentric chromosome organization across highly divergent haplotypes. We identified an XY sexual system with a small sex-determining region on chromosome 8. Transcriptomic changes during dehydration varied with the severity of water loss and pointed to early suppression of growth, progressive activation of protective mechanisms, and reversible changes in transcript abundance upon rehydration. Co-expression networks and targeted gene family analyses revealed dynamic regulation of LEA and ELIP genes, with evidence of transcriptome "priming" in hydrated plants, with transcript abundance shifting toward highly disordered proteins during desiccation. Enrichment of ABA and light-responsive cis-regulatory elements in key genes support the existence of conserved stress response pathways. M. flabellifolias rich profile of phenolics and antioxidant genes highlight the overlap between desiccation tolerance and medicinal potential. Together, this study provides foundational resources for understanding the genomic architecture and reproductive biology of M. flabellifolia while offering new insights into the mechanisms of desiccation tolerance.