RESEARCH
Transcriptional regulation of the iron-deficiency response
Iron is an essential nutrient required for life in nearly all organisms, and iron deficiency is one of the most prevalent nutritional deficiencies in humans. While much of the world’s population relies on plants as the primary source of iron, nearly a third of the world's soils are iron limited, giving great importance to understanding the uptake and transport of iron in plants. Additionally, though iron is essential for plant growth and development, the same properties that make this transition metals indispensable can also make it deadly in excess, necessitating tight regulation of iron homeostasis. My dissertation research focused on understanding the transcriptional regulation of key factors in the iron deficiency response. Understanding this pathway will allow us to better modulate iron regulation and accumulation in plants, with the eventual goal of increasing the quantity of iron in the foods that people rely on.
When plants sense iron deficiency, they initiate a response that includes changes in the expression of hundreds of genes (Palmer and Guerinot, 2009). Despite the many changes in gene expression, only one transcription factor had been identified as essential for this response at the beginning of my dissertation. Through my dissertation work in the Guerinot lab at Dartmouth College, we were able to identify several proteins critical for survival of plants under conditions of iron deficiency, a problem found in nearly a third of the world's soils. We found that two MYB transcription factors, MYB10 and MYB72, are highly induced under iron deficiency in the plant root (Figure 1). These factors act in a semi-redundant manner to regulate expression of the nicotianamine synthase gene, NAS4, which is involved in the production of nicotianamine, a crucial metal chelator involved in the transport of iron (Figure 2). Without these factors, plants are unable to survive on iron deficient soils (Figure 3). (Palmer, et al., 2013).
Figure 1. MYB10 and MYB72 are expressed in the root under iron deficiency. GUS expression in the roots of stable MYB10-GUS and MYB72-GUS lines in a wildtype background, grown under iron sufficient or deficient conditions. Modified from Palmer, et al., 2013. |
Figure 2. MYB10 and MYB72 are required for NAS4 expression under iron deficiency.
qPCR on root tissue from wildtype (Col) and myb10myb72 double mutant plants grown under iron sufficiency or deficiency. Modified from Palmer, et al., 2013. |
Figure 3. MYB10, MYB72, and NAS4 are required for survival under iron deficiency.
Plants were grown for 3 weeks on soil under normal, alkaline (iron-limiting), and alkaline +Fe (iron excess) conditions. Iron was added by watering the plants with 500 µM FeEDDHA. Modified from Palmer, et al., 2013.
Plants were grown for 3 weeks on soil under normal, alkaline (iron-limiting), and alkaline +Fe (iron excess) conditions. Iron was added by watering the plants with 500 µM FeEDDHA. Modified from Palmer, et al., 2013.