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 (TZ) where they start differentiating. The balance between cell division and cell differentiation is regulated by two antagonistic hormones - auxin that promotes cell division and cytokinin that promotes cell differentiation ¿ which interact with each other through an elegantly simple regulatory circuit.
Aim of this project is to understand how changes in auxin level mediated by cytokinin via this regulatory circuit control the position of the TZ developmental boundary thus determining meristem size, and how environmental stimuli are integrated in this circuit in affecting root growth.
This will be achieved through a combination of state of the art genetic, molecular and cell biology approaches including single and multiple mutants, cell-specific gene expression, fluorescence-activated cell sorting (FACS) coupled to expression profiling and tissue¿specific microarray analysis.
The results foreseen in this proposal will shed light on the molecular mechanisms through which the ARR1/SHY2/PIN/GH3 circuit controls root meristem size from the LCR, and how this module perceives environmental (abiotic) stimuli and modulates root growth accordingly. While the molecular mechanisms involved in stem cell positioning and activity are partially comprehended, the regulatory networks controlling the shift from transit-amplifying identity to differentiation are still poorly understood, as are the mechanisms that act in positioning this developmental boundary. Still very poorly understood are also the mechanisms underlying the modulation of root growth by exogenous inputs.
In this perspective, the work proposed will lead to groundbreaking 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 positioning developmental boundaries control growth and development of all organs of the plant.
- The positioning of developmental boundary between cell differentiation and cell division - is a crucial issue also in animal development.
- Understanding the basic aspects of root growth response to environmental inputs will have a significant impact on agronomical practices through the development of new breeding strategies.