Expression of the IRT1 Metal Transporter Is Controlled by Metals at the Levels of Transcript and Protein Accumulation

Abstract

Iron, an essential nutrient, is not readily available to plants because of its low solubility. In addition, iron is toxic in excess, catalyzing the formation of hydroxyl radicals that can damage cellular constituents. Consequently, plants must carefully regulate iron uptake so that iron homeostasis is maintained. The Arabidopsis IRT1 gene is the major transporter responsible for high-affinity iron uptake from the soil. Here, we show that the steady state level of IRT1 mRNA was induced within 24 h after transfer of plants to iron-deficient conditions, with protein levels peaking 72 h after transfer. IRT1 mRNA and protein were undetectable 12 h after plants were shifted back to iron-sufficient conditions. Overexpression of IRT1 did not confer dominant gain-of-function enhancement of metal uptake. Analysis of 35S-IRT1 transgenic plants revealed that although IRT1 mRNA was expressed constitutively in these plants, IRT1 protein was present only in the roots when iron is limiting. Under these conditions, plants that overexpressed IRT1 accumulated higher levels of cadmium and zinc than wild-type plants, indicating that IRT1 is responsible for the uptake of these metals and that IRT1 protein levels are indeed increased in these plants. Our results suggest that the expression of IRT1 is controlled by two distinct mechanisms that provide an effective means of regulating metal transport in response to changing environmental conditions.

Alleviating Effect of Exogenous Application of Ascorbic Acid on Growth and Mineral Nutrients in Cadmium Stressed Barley (Hordeum vulgare) Seedlings

“…Hence, Cd addition reduced the shoot fresh and dry weight also have been studied previously in different plant species such as wheat (Mane et al, 2010) and barley (Zaltauskaite and Sliumpaite, 2013). Cadmium may impede with nutrient uptake due to competition for the same transmembrane carriers, thereby leading to the altered tissue nutrient contents (Connolly et al, 2002). These interactions between Cd and other essential nutrients may lead to physiological disarrays as well as a reduction in growth (ElBeltagi et al, 2010).…”

Proteasome‐mediated turnover of the transcriptional activator FIT is required for plant iron‐deficiency responses

“…To evaluate the biological significance of such a regulatory mechanism, we determined the timing of FIT post-transcriptional regulation visualized by the decrease in constitutively expressed FIT-GFP in Col/35S::FIT-GFP plants, compared with other known responses to iron starvation. The most commonly used and robust marker for the establishment of these early molecular responses is the accumulation of IRT1 protein in roots (Connolly et al, 2002). Time-course analyses of protein accumulation by western blot revealed that in our conditions, IRT1 protein starts to accumulate 24-48 h after transfer to iron-limiting conditions, and keeps increasing until day 5 (Figure 3a).…”

The Arabidopsis Mediator subunit MED16 regulates iron homeostasis by associating with EIN3/EIL1 through subunit MED25

“…However, the IRT1 protein is not specific for iron. Other metals such as Zn 2+ , Mn 2+ and Co 2+ can be transported into plants via the IRT1 protein in Arabidopsis (Eide et al, 1996;Korshunova et al, 1999;Connolly et al, 2002;Henriques et al, 2002;Varotto et al, 2002;Vert et al, 2002). Following transportation into root cells, iron is chelated by citrate or nicotianamine and distributed to the shoots (Stephan and Scholz, 1993;Briat et al, 2007).…”