Plants, just like animals require nourishment for growth and survival. Plants acquire nutrients from surrounding soil for allocation to various plant organs where nutrients can be made bio-available for animals to take up in form of food. In both organisms some nutrients are required in large amounts while others are needed in smaller quantities. The latter are known as trace minerals or micronutrients which include Zinc, Iron, Manganese, and Copper.
Iron is an essential micronutrient for both plants and animals. In plants iron plays an important role as a cofactor in chlorophyll synthesis and in photosynthetic electron transport reactions which are key to plant growth and development. Iron is also important in the plant’s defenses against invading microbes. Iron deficiency in plants shows as visible interveinal leaf chlorosis and reduced plant biomass leading to low crop yields. On the other hand, iron excess is harmful to the plant as it may cause cell death. Thus plants have evolved several strategies to regulate the mineral’s acquisition from surrounding soil and utilization within the plant.
Plants provide a rich iron source for humans as it is availed in leaves, fruits and seeds. Iron is acquired by plant roots from soil rhizospehere where it is made bioavailable. Iron is then translocated to the shoot organs via the vascular system, xylem and phloem. In shoots, the mineral is highly distributed to the leaves as it is involved in photosynthetic processes whereby plants use sunlight to convert carbon dioxide and water into simple sugars.
Unlike animals, plants are immobile organisms and hence need to adapt to a range of abiotic stresses such as nutrient starvation during their growth lifetime. Similarly plants can sense iron limitation in their growth surrounding and develop mechanisms to aid their survival. Such responses may include among the following:
- Change of plant growth traits, for example, root elongation and lateral root formation. This enables the plant to access more soil surfaces where iron and other minerals may be highly bio-available for uptake,
- Increased translocation of iron from root-to-shoot whereby long-distance communication and signaling between shoot-to-root is enabled. This takes place via the plant vascular system (see Figure 1),
- Increased efficiency of iron loading from the organs in which it was temporarily stored for releasing to tissues where it might be highly needed.
All three responses involve mechanisms for the plant to overcome iron limitation and increase its acquisition, redistribution and utilization. To ensure coordination of iron deficiency responses, plants deploy a set of “molecular switches”. These involve genes encoding various proteins that tightly regulate the responses to avoid iron overloading. As their name suggests the “molecular switches” can be turned ON or OFF depending on how much of the mineral is available around the plant’s surroundings and how much of it may be needed within the plant. The genes positively or negatively interact forming a gene regulation network that fine-tunes whole plant iron homeostasis.
To better understand how iron acquisition and allocation responses are coordinated, my PhD work focuses on investigating how the involved gene regulatory networks adjust with plant developmental processes. In particular, I aim to understand how iron deficiency genes and transcription factors are regulated in different shoot organs including inflorescence organs, leaves, and stems under changing iron conditions and across plant lifecycle. It is likely that iron homeostasis also interacts with other environmental signals such as light to enable plant developmental processes which require constant adjustment of iron utilization. Understanding of correlations between iron homeostasis with shoot developmental processes will impact breeding efforts for nutritionally enriched crops.
Under the heading Planter’s Punch we present each month one special aspect of the CEPLAS research programme. All contributions are prepared by our young researchers.
Mary Ngigi is a PhD student working in the group of Petra Bauer at the Intitute of Botany (HHU) since 2021. Their research focuses on plant iron nutrition, specifically in the genetic factors that control iron acquisition and utilization in the model Arabidopsis thaliana and in crop plants. Previously she obtained a Bachelor’s degree in Biotechnology from Kenyatta University, Kenya where she developed an interest in plant molecular biology.
R. Ivanov, T. Brumbarova, and P. Bauer, Fitting into the harsh reality: Regulation of iron-deficiency responses in dicotyledonous plants, Mol. Plant, vol. 5, no. 1, pp. 27–42, 2012, doi: 10.1093/mp/ssr065.
B. Schwarz and P. Bauer, “FIT, a regulatory hub for iron deficiency and stress signaling in roots, and FIT-dependent and -independent gene signatures,” J. Exp. Bot., vol. 71, no. 5, pp. 1694–1705, 2020, doi: 10.1093/jxb/eraa012.
Gao, F., Robe, K., Gaymard, F., Izquierdo, E., & Dubos, C. (2019). The transcriptional control of iron homeostasis in plants: A tale of bHLH transcription factors? In Frontiers in Plant Science (Vol. 10, p. 6). Frontiers Media S.A. doi.org/10.3389/fpls.2019.00006.