A cis-regulatory element of the PHYTOCHROME A gene confers the submergence escape capacity for amphibious plants

Amphibious plants escape submergence by plastically accelerating shoot growth, yet the mechanism underlying this convergent strategy remains unclear. Here, we demonstrate that PHYTOCHROME A (PHYA), a light photoreceptor, acts as a central regulator of the contrasting submergence escape capacities between amphibious Alternanthera philoxeroides and its terrestrial congener A. pungens. PHYA is distinctively regulated upon submergence in two congeners and negatively regulates submergence-induced elongation. Crucially, we find a cis-regulatory element (CRE) variant in the PHYA promoter between two congeners, which governs EIN3-dependent transcriptional repression and drives species-specific PHYA expression. Expanded investigation unveils phyletic retention of this CRE in other amphibious species, providing preliminary evidence for convergent evolution in the submergence escape capacity through independent co-option of the same CREs. Our findings demonstrate a role of PHYA in mediating submergence responses, deepen the understanding of the molecular basis for plant secondary aquatic adaptation, and inform flood-resilient crops engineering via cis-regulatory manipulation.