title: Chromate alters root system architecture and activates expression of genes involved in iron homeostasis and signaling in Arabidopsis thaliana.
abstract: Soil contamination by hexavalent chromium [Cr(VI) or chromate] due to anthropogenic activities has become an increasingly important environmental problem. To date few studies have been performed to elucidate the signaling networks involved on adaptive responses to (CrVI) toxicity in plants. In this work, we report that depending upon its concentration, Cr(VI) alters in different ways the architecture of the root system in Arabidopsis thaliana seedlings. Low concentrations of Cr (20-40 µM) promoted primary root growth, while concentrations higher than 60 µM Cr repressed growth and increased formation of root hairs, lateral root primordia and adventitious roots. We analyzed global gene expression changes in seedlings grown in media supplied with 20 or 140 µM Cr. The level of 731 transcripts was significantly modified in response to Cr treatment with only five genes common to both Cr concentrations. Interestingly, 23 genes related to iron (Fe) acquisition were up-regulated including IRT1, YSL2, FRO5, BHLH100, BHLH101 and BHLH039 and the master controllers of Fe deficiency responses PYE and BTS were specifically activated in pericycle cells. It was also found that increasing concentration of Cr in the plant correlated with a decrease in Fe content, but increased both acidification of the rhizosphere and activity of the ferric chelate reductase. Supply of Fe to Cr-treated Arabidopsis allowed primary root to resume growth and alleviated toxicity symptoms, indicating that Fe nutrition is a major target of Cr stress in plants. Our results show that low Cr levels are beneficial to plants and that toxic Cr concentrations activate a low-Fe rescue system.
authors.affiliation: Facultad de Biología, Universidad Michoacana de San Nicolás de Hidalgo, Edificio R, Ciudad Universitaria, C. P. 58030, Morelia, Michoacán, Mexico.
authors.forename: Miguel
authors.initials: M
authors.lastname: Martínez-Trujillo
authors.forename: Alfonso
authors.initials: A
authors.lastname: Méndez-Bravo
authors.forename: Randy
authors.initials: R
authors.lastname: Ortiz-Castro
authors.forename: Fátima
authors.initials: F
authors.lastname: Hernández-Madrigal
authors.forename: Enrique
authors.initials: E
authors.lastname: Ibarra-Laclette
authors.forename: León Francisco
authors.initials: LF
authors.lastname: Ruiz-Herrera
authors.forename: Terri A
authors.initials: TA
authors.lastname: Long
authors.forename: Carlos
authors.initials: C
authors.lastname: Cervantes
authors.forename: Luis
authors.initials: L
authors.lastname: Herrera-Estrella
authors.forename: José
authors.initials: J
authors.lastname: López-Bucio
mesh_terms: D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D002840:Chromates / Q000633:toxicity*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D007501:Iron / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D036226:Seedlings / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects; D012989:Soil Pollutants / Q000633:toxicity*
chemical_list: D002840:Chromates; D012989:Soil Pollutants; D007501:Iron