Global population increases and climate change underscore the need for better comprehension of how plants acquire and process nutrients such as iron. Using cell type-specific transcriptional profiling, we identified a pericycle-specific iron deficiency response and a bHLH transcription factor, POPEYE (PYE), that may play an important role in this response. Functional analysis of PYE suggests that it positively regulates growth and development under iron-deficient conditions. Chromatin immunoprecipitation-on-chip analysis and transcriptional profiling reveal that PYE helps maintain iron homeostasis by regulating the expression of known iron homeostasis genes and other genes involved in transcription, development, and stress response. PYE interacts with PYE homologs, including IAA-Leu Resistant3 (ILR3), another bHLH transcription factor that is involved in metal ion homeostasis. Moreover, ILR3 interacts with a third protein, BRUTUS (BTS), a putative E3 ligase protein, with metal ion binding and DNA binding domains, which negatively regulates the response to iron deficiency. PYE and BTS expression is also tightly coregulated. We propose that interactions among PYE, PYE homologs, and BTS are important for maintaining iron homeostasis under low iron conditions.

Little is known about the way developmental cues affect how cells interpret their environment. We characterized the transcriptional response to high salinity of different cell layers and developmental stages of the Arabidopsis root and found that transcriptional responses are highly constrained by developmental parameters. These transcriptional changes lead to the differential regulation of specific biological functions in subsets of cell layers, several of which correspond to observable physiological changes. We showed that known stress pathways primarily control semiubiquitous responses and used mutants that disrupt epidermal patterning to reveal cell-layer-specific and inter-cell-layer effects. By performing a similar analysis using iron deprivation, we identified common cell-type-specific stress responses and revealed the crucial role the environment plays in defining the transcriptional outcome of cell-fate decisions.