Expression analysis of root pericycle cell-types after iron deficiency (-Fe) treatment

Pericycle specific transcriptional profiles were generated by FACS (Fluorescence Activated Cell Sorting) of roots that express a pericycle-specific GFP-reporter. FACS cell populations were isolated from roots grown under standard conditions or roots that had been transferred to -Fe media for 24 hours. Global population increases and climate change underscore the need for better comprehension of how plants acquire and process nutrients such as iron. A systems biology approach was taken to elucidate novel regulatory mechanisms involved in plant responses to iron deficiency (-Fe). Using cell-type specific transcriptional profiling we identified a pericycle-specific iron deficiency response, and a previously uncharacterized transcription factor, POPEYE (PYE), that plays an important role in this response. Functional analysis of PYE suggests that it positively regulates growth and development under iron deficient conditions. ChIP-on-chip analysis and transcriptional profiling reveal that PYE helps maintain iron homeostasis by directly and indirectly regulating the expression of ferric reductases, metal ion transporters, iron storage proteins, and other key iron homeostasis genes. In addition to PYE, we also identified a second protein BRUTUS (BTS), which appears to negatively regulate the response to iron deficiency. BTS is a unique putative E3 ligase protein, with metal ion binding and DNA binding domains. PYE and BTS are tightly co-regulated and physically interact with PYE paralogs, one of which is thought to positively regulate expression of genes involved in iron homeostasis. We propose that iron content is sensed within the pericycle where PYE, perhaps in conjunction with BTS and other regulatory proteins, is then activated to control a regulatory network involved in maintaining proper iron distribution in plants. Keywords: Cell-type specific analysis of stress response using FACS To determine how the pericycle responds to -Fe 6 day old GFP-reporter lines, in which pericycle cells are marked, were germinated under standard growth conditions, then shifted to standard media (control, MS media) or iron deficient media (-Fe, 0.3mM Ferrozine in MS media containing no ferrous sulfate) for 24 hours before protoplasting and sorting. A file with Q-values that indicate the statistical significance of the difference in expression between + and -Fe for each probeset is linked at the foot of this record.