However, no study has examined whether the iron-responsive PYEL proteins that BTS interacts with are targeted by this E3 ligase activity. and PYE-like (PYEL) basic helix-loop-helix transcription factors occur within the nucleus and are dependent on the FR167344 free base presence of the RING domain. We provide evidence that FR167344 free base BTS facilitates 26S proteasome-mediated degradation of PYEL proteins in the absence of iron. We also determined that, upon binding iron at the HHE domains, BTS is destabilized and that this destabilization relies on specific residues within the HHE domains. This study reveals an important and unique mechanism for plant iron homeostasis whereby an E3 ubiquitin ligase may posttranslationally control components of the transcriptional regulatory network involved in the iron deficiency response. Iron deficiency is a critical issue for most living organisms because iron is an essential component of many metabolic processes. Excess iron can be equally problematic due to its potential to react with oxygen and form damaging reactive oxygen species. Consequently, plants and animals tightly regulate their responses to iron bioavailability. Plants have evolved two primary ways to uptake iron from soil. Under low-iron conditions, grasses such as rice (Oryza sativa) and maize (Zea mays) primarily utilize the Strategy II response, whereby they release phytosiderophores into the rhizosphere that bind to ferric iron with high affinity. Phytosiderophore-ferric iron complexes are transported into the root via membrane-localized yellow stripe and yellow stripe-like (YSL) transporters (Curie et al., 2001;Inoue et al., 2009), although several studies suggest that rice is also able to directly uptake ferrous iron (Ishimaru et al., 2006;Cheng et al., 2007). Dicots and nongraminaceous monocots utilize the Strategy I response under low-iron conditions. In Arabidopsis (Arabidopsis thaliana), the Strategy I response involves an increase in the expression and activity of proton-translocating adenosine triphosphatases (H+-ATPases), most notably AHA2, which acidifies the rhizosphere and increases the solubility of ferric iron FR167344 free base oxides near the root epidermis (Rmheld et al., 1984;Santi and Schmidt, 2009). There is also an increase in the expression and activity of the membrane-bound iron reductase FERRIC REDUCTASE OXIDASE2 (FRO2), which reduces ferric iron to ferrous iron (Robinson et al., 1999). Ferrous iron is FR167344 free base then FR167344 free base transported into epidermal cells via IRON-REGULATED TRANSPORTER1 (IRT1), a membrane-localized metal ion transporter that transports iron and other metal ions, including zinc, manganese, and cadmium (Eide et al., 1996;Vert et al., 2002;Colangelo and Guerinot, 2004). After uptake, iron is bound to chelators such as nicotianamine and citrate and subsequently translocated into and throughout the vasculature (Durrett et al., 2007;Curie et al., 2009). This coordinated iron deficiency response is controlled by the basic helix-loop-helix (bHLH) transcription factor FER-LIKE FE DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT;Colangelo and Guerinot, 2004). FIT acts in concert with two other bHLH proteins (Yuan et al., 2008), ETHYLENE INSENSITIVE3 and ETHYLENE INSENSITIVE3-LIKE1 (Lingam et al., 2011), and is posttranslationally regulated by the presence of nitric oxide via 26S proteasome-dependent degradation (Meiser et al., 2011;Sivitz et al., 2011). A FIT-independent iron homeostasis pathway has also been identified involving bHLH100 and bHLH101 (Sivitz et al., 2012). Recently, it has been shown that root exudates including phenolics and riboflavin derivatives function as iron-binding compounds in Arabidopsis andMedicago truncatula, similar to those in the chelation-based Strategy II response. The induction of phenylpropanoid and flavin pathway genes is tightly linked to core genes of the iron acquisition machinery, such as FIT, FRO2, IRT1, and AHA2, and thus appears to constitute an integral component of the Strategy I response in Arabidopsis Rabbit Polyclonal to Cytochrome P450 3A7 andM.truncatula(Rodrguez-Celma et al., 2013). We reported that the bHLH protein POPEYE.
