In the Arabidopsis thaliana root, stem cells divide in the apical stem cell niche of the meristem and originate daughter cells that divide until they reach a distal boundary denominated transition zone where they start differentiating. At the end of root meristem development a balance between cell division and cell differentiation is reached to maintain indeterminate root grow. This balance is regulated by the antagonistic interaction of two hormones: auxin that promotes cell division, and cytokinin that promotes cell differentiation.
Cytokinin controls cell differentiation via the ARR1 transcription factor, specifically expressed at the transition zone. Aim of this project is to understand the role of a newly identified transcription factor, ARR10 that, unlike ARR1, is expressed in the meristem where cells are still dividing. These observations, together with the analysis of arr10 knock out mutants, suggest the interesting hypothesis that ARR10 contributes to balance cell division with cell differentiation repressing, in the meristem, cell division. As such cytokinin, by activating at the same time ARR1 at the transition zone and ARR10 in the meristem, establish the balance of cell division with cell differentiation, thus ensuring indeterminate root grow.
The results foreseen in this proposal will shed light on the molecular mechanisms through which ARR10 controls root development, and, in particular, how ARR10 is involved in balancing cell division with cell differentiation to ensure indeterminate root growth. While the molecular mechanisms involved in stem cell positioning and activity are partially comprehended, the regulatory networks controlling the shift from dividing cell to differentiating cell are still poorly understood, as are the mechanisms that act in balancing cell division with cell differentiation.
In this perspective, the work proposed will lead to very interesting scientific results.
It should also be pointed out that:
- The results foreseen in this proposal will have an impact beyond the organ being studied: most likely, in fact, analogous hormonal regulatory networks, balancing cell division with cell differentiation, control growth and development of all organs of the plant.
- Understanding how cell division is balanced with cell differentiation is a crucial issue also in animal development: interestingly several mechanistic similarities have already been observed during root meristem development and growth of mammalian bones and the gut crypt (1).
- Understanding the basic aspects of root growth will have a significant impact on agronomical practices through the development of new breeding strategies.
Root architecture critically influences nutrient and water uptake efficiency. For example, rooting depth impacts the efficient acquisition of nitrogen (and water), since nitrate leaks down the soil profile. To this end, a detailed characterisation of root development and consequently control of the overall architecture of the root system, are imperative for improving crop performance.
1) Spradling et al., (2001), Nature 414 :98-104.