Transcriptional Responses to Fire in Three Savanna Grass Species: Candidate Pathways for Fire-Stimulated Flowering

Aristida beyrichiana (wiregrass) is a grass species in the southeastern U.S. that exhibits pronounced fire-stimulated flowering, an adaptive trait in fire-prone ecosystems. Although fire-stimulated flowering has been well documented morphologically in this species, its molecular basis remains largely unknown. To investigate species-specific drivers of this adaptation, we performed comparative transcriptomic analyses under natural field conditions, before and approximately seven weeks after a prescribed fire, on wiregrass and two other grass species, Aristida spiciformis (bottlebrush threeawn) and Sporobolus junceus (pineywoods dropseed), which are not known to rely on fire to induce flowering. All species showed upregulation of conserved stress-related genes after fire, yet wiregrass exhibited a more focused transcriptional response. Notably, genes involved in nitrogen remobilization (ASN1, GDH2) and carbohydrate metabolism (SUS4, TPS10, DPE2) were uniquely upregulated in wiregrass, suggesting candidate metabolic adaptations that may support rapid post-fire regrowth and flowering. We also detected non-coding RNAs among the differentially expressed genes in wiregrass, pointing to a possible additional layer of regulation in fire-induced responses. Collectively, these results provide new transcriptomic insight into post-fire responses in wiregrass and identify candidate genes and regulatory pathways that require functional validation; because the observed expression differences integrate fire-induced, developmental and seasonal effects, they should not be interpreted as direct fire-specific responses.