NITRATE ABSORPTION
Introduction
The NCBS-TIFR(National Centre of Biological Sciences-Tata Institute of Fundamental Research) found that there is a new pathway in plants to absorb nitrates.
Mechanism
- The gene MADS27, which regulates nitrate absorption, root development and stress tolerance is activated by the micro-RNA, miR444, therefore, offers a way to control these properties of the plant.
- This mechanism was studied in both rice(monocot) and tobacco(dicot) plants.
Nitrogen
- Nitrogen is the most important macronutrient needed for the development of a plant.
- It is a part of chlorophyll, amino acids and nucleic acids.
- Nitrogen is mostly sourced from the soil, where it is mainly absorbed in the form of nitrates and ammonium by the roots.
- Nitrates also play a role in controlling genome-wide gene expression that in turn regulates root system architecture, flowering time, and leaf development.
- A lot of actions take place in roots to absorb and convert nitrogen into useful nitrates, the absorbed nitrates in turn regulate plant development apart from being useful as a macronutrient.
Nitrate Overuse
- The presence of nitrates is important for plant development and also for grain production.
- The overuse of nitrates in fertilizers can lead to the dumping of nitrates in the soil which leads to the accumulation of nitrates in water and soil.
- This accumulation adds to soil and water pollution and increases the contribution to greenhouse gases.
- To avoid this, there should be the optimal use of nitrates.
- As the whole process of nitrate absorption takes place in the roots, a well-developed root system is needed for this to occur optimally.
- Auxin is responsible for well-developed roots across all plants.
- A number of genes are known to help with auxin production, improved nitrate transport and assimilation in plants.
Regulatory Switches
- In monocot plants, several regulatory switches that regulate nitrate absorption and root development like micro-RNA, and miR444 are known.
- The micro-RNA “miR444” is specific to monocots. When this is not made, its target, MADS27 is produced in a higher amount which improves biosynthesis and transport of the hormone auxin, which is key for root development and branching.
- This regulatory miR444 switch is known to turn off at least five genes called MADS-box transcription factor genes.
- The speciality of the MADS-box transcription factors is that they function like switch boxes of their own.
- They bind to their favourite specific DNA sequences and they switch the neighbouring genes “on”.
Three Prolonged Effect
- The transcription factor miR444 called MADS27 has a three-pronged effect on the plant.
- First, it regulates nitrate absorption by switching “on” proteins involved in this process.
- Second, it leads to better development of the roots by regulating the auxin hormone production and transportation.
- Finally, it helps in the abiotic stress tolerance by keeping the main stress player proteins” on”.
- This provides an alternate means of regulating and optimizing nitrate absorption.
Dicot Plants
- MADS27 works to improve three factors- nitrate absorption, root development and stress tolerance with the help of RNA analysis and after finding to which part of the genome this genome transcription binds.
- Many experiments were conducted on the tobacco plant.
- The gene MADS27 appears to be an excellent candidate to modify in order to develop nitrogen use efficiency, which is something that helps the plant absorb more nitrates and to engineer abiotic stress tolerance.
- Tinkering MADS27 expression by genome editing is the next step so that the modified plants are acceptable to use directly.
Goal
The larger goal is to understand the role of epigenetics in regulating expression of important genes.
