Self-funded PhD - Growing pains – how do plants measure developmental time?

About the Project

During their life-cycles multicellular organisms progress through a series of different developmental phases. To ensure that development occurs in the right sequence and at an appropriate rate, the correct timing of transitions between phases is essential. Understanding how organisms coordinate phase transitions is therefore a key question in developmental biology. In the case of plants, much of what we understand about the regulation of developmental timing comes from studies of the switch from vegetative to reproductive growth. However, it is unclear how widely these mechanisms are used in the control of other developmental transitions. An additional attractive, but understudied, model for the study of developmental timing in plants is vegetative phase change. Vegetative phase change describes the switch from juvenile to adult stages of vegetative growth and, depending on the species, is manifested in a wide variety of traits. In addition to the phenotypic changes associated with vegetative phase change, the process is regulated by a highly conserved genetic network - the master regulator of vegetative phase change, the microRNA miR156, evolved in the ancestor of all land plants. Furthermore, the process is developmentally robust, predictable and less sensitive to environmental stimuli than flowering. Vegetative phase change is therefore an ideal system to study developmental timing in plants. Integrating a range of genetic analyses, aim of this studentship is to understand how miR156 functions as a developmental clock.

The overall levels of miR156 decline during development, triggering the transition to adult growth. The decrease in miR156 accumulation over time is largely determined by the transcription patterns of two genes: MIR156A and MIR156C. To elucidate how MIR156A/C function as developmental timers, this project aims to characterise the regulatory networks that regulate their expression patterns. Specifically, the student will:

1. Contribute to a collaborative effort in the lab to identify cis-regulatory elements in the promoters of MIR156A/C that coordinate their temporal expression patterns
2. Generate new transcriptional reporters of MIR156A/C fused to luciferase to visibly reveal temporal expression patterns – these will then be used for a high-throughput mutant screen.
3. Produce transgenic lines with deletions of the MIR156A/C loci to reveal which regions contribute to their temporal decline
4. Carry out biochemical assays of DNA-protein binding to confirm the function of a candidate regulatory transcription factor.

In combination, the results of this studentship will provide critical insights into how plants decide when to ‘grow up’. This will not only increase our understanding of vegetative phase change but will also impact our understanding of developmental timing mechanisms in plants more generally. In addition, as the timing of developmental transitions have important effects on crop yields, they are also likely to lead to discoveries that can be used to generate higher yielding and more robust crops.

This project will provide fundamental training in genetic analysis, including experience with molecular cloning, transgenic plant production and quantification of gene expression. In addition to direct supervision by Dr. Jim Fouracre, the student will benefit from interactions with multiple world leading groups working in the communal Bristol plant molecular biology research lab.

For more information or to discuss this project in further detail please contact jim.fouracre@bristol.ac.uk. With multiple approaches to elucidate the molecular mechanism of vegetative phase change, the student will be able to identify which strategy and techniques they feel are most viable and focus on these to achieve their research objectives. I would be very happy to consider alternative approaches potential students would like to incorporate into this research project.