Adaptation at the Extremes: Halophytes and Metallophytes as Ecological Models and Biotechnological Resources

Abstract

Salinisation and metal contamination are among the leading causes of arable land loss worldwide, yet halophytes and metallophytes—the plants best adapted to these conditions—remain a considerably underexploited biotechnological resource. Using an eco-evo-devo perspective, in which environmental pressure, developmental plasticity and evolutionary outcome interact to shape adaptive traits, we examine evidence that salinity and metal tolerance arose independently and repeatedly across distant angiosperm lineages, converging on comparable structural and physiological solutions: succulence, anatomical transport barriers, root exudation, osmoprotection, and ion compartmentalisation. This convergence distinguishes stress-tolerance mechanisms that are general from those that are stressor-specific, informing efforts to transfer these traits into other extremophytes and conventional crops. In turn, we assess the ecological roles of halophytes and metallophytes in their natural habitats before evaluating their biotechnological applications, which range from halophyte-derived genes and promoters for crop improvement to halophyte biomass for bioenergy, biomaterials and remediation of saline, polluted soils and wastewaters, while metallophytes underpin phytoremediation, phytomining, and biomonitoring of metal-contaminated sites. Notwithstanding this progress, wider exploitation remains limited by the scarcity of crop-relevant gene-editing platforms for halophytes, low biomass yield in metal-hyperaccumulating species, and inconsistent phytochemical standardisation across growing conditions, as well as by three unresolved gaps: the lack of methods to partition host and microbiome contributions to tolerance, uncertainty over whether mechanisms shared between the two groups are convergent or evolutionarily conserved, and the undetermined contribution of epigenetic inheritance to stress adaptation. Translating this evolutionary and physiological knowledge into stress-adapted cultivars, optimised extraction systems, and field-ready phytoremediation and phytomining programmes is central to addressing land degradation, food security, and sustainable resource recovery.