Cross‐Species Plasticity and Divergence Under Alkaline Soil Signature Conditions Differentiating PYE From FIT Target Transcripts in the Arabidopsis thaliana Ferrome

Soil pH is an influential abiotic environmental factor. Here, we identify responses to central stimuli associated with calcareous alkaline soils in Arabidopsis and comparatively explore the potential of the closely related Arabidopsis halleri for addressing how plants cope with local soil pH. We profiled the root transcriptome upon applying a set of hydroponic treatments-low bioavailable iron (Fe), alkaline pH and both in combination. Among the known Fe deficiency responses (ferrome), pervasively Fe-deficiency responsive transcripts (pIDR) encoding the transcription factor PYE and its targets responded co-directionally to Fe deficiency also at pH 7.5. A distinct subgroup of additionally alkaline-pH-responsive transcripts (aAPRs), comprising FIT and FIT-dependent genes, showed a co-directional response to pH 7.5 even with available Fe. Root hair densities in both species increased at an alkaline pH. Compared with A. thaliana, A. halleri accessions from soils of contrasting pH showed elevated tolerance to low-Fe and alkaline pH based on chlorophyll content and root growth. A. halleri from high-pH soils convergently exhibited longer and less branched root systems, more stable ionomes across conditions, and attenuated root growth at alkaline pH with Fe. Our findings provide insights into Fe-deficiency regulatory networks and identify soil pH-related phenotypic divergence within A. halleri and across species.