Interaction of auxin and strigolactone in the regulation of carpic dominance

Lead Research Organisation: University of Leeds
Department Name: Sch of Biology

Abstract

Background
Seeds produced during plant reproduction are known to communicate with each other, and seeds in older/more vigorous fruits are able to limit or abort the development of new fruits/seeds. The mechanisms that drive this phenomenon ('carpic dominance') are poorly characterised, but preliminary data suggest the phytohormones strigolactone and auxin play key roles.

Objectives
1. Analyse the role of strigolactone and auxin in carpic dominance.
2. Identify transcriptional responses that result in carpic dominance.
3. Define environmental signals that modulate carpic dominance in crop species.

Novelty
Although the phenomenon of carpic dominance is long-recognized, very little work has been undertaken, especially in the molecular genetic era. This project thus represents a highly novel area in plant developmental biology.

Timeliness
There is a pressing need to increase crop yields to feed an expanding global population. This project is thus exceptionally timely, since carpic dominance is a major limit on seed set, and understanding it could unlock rapid increases in yield potential.

Experimental Approach
To define the role of strigolactone and auxin in carpic dominance, we will exploit existing molecular genetic tools in the model plant Arabidopsis, including auxin/strigolactone mutants and reporter lines. We will also develop tools in the crop plant tomato (which has strong carpic dominance) to perform live imaging of auxin/strigolactone dynamics during fruit development. We will use RNA-seq to identify transcriptional changes that occur in both dominant and dominated fruit/seeds during carpic dominance, and will then test the role of identified candidate genes in the phenomenon using reverse genetic analyses. We will also use both field and glasshouse experiments in the crop species oilseed rape (a close relative of Arabidopsis), to identify the environmental signals that modulate the extent of carpic dominance, and to transfer knowledge generated in Arabidopsis to field/agricultural contexts.

This project aims to understand the biochemical, genetic and cellular mechanisms that form the basis of the carpic dominance phenomenon in plants. It is therefore deeply rooted in mechanistic biology at the molecular and cellular level. The project is an excellent fit with the remit of the agriculture and food security research area. Global food security will require increased yield from major crop species, and carpic dominance acts as a major limit on yield in many of these species. If we can understand the mechanistic basis of carpic dominance, we can breed crop species with reduced carpic dominance, which could result in a step-change in yield, without the need for more intensive inputs (e.g. fertilizer).

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
BB/M011151/1 30/09/2015 29/09/2023
2110700 Studentship BB/M011151/1 30/09/2018 31/10/2022 Catriona Walker
 
Description There has been very little previous research carried out into the end of flowering in plants. Our work has examined this in more detail, and has provided significant new knowledge in the area. An original study by Hensel et al (1994) was one of the key inspirations for this work, and suggested that the end of flowering is brought about by a global, seed-derived signal, bringing about simultaneous end of flowering across the whole plant. This was termed 'Global Proliferative Arrest' (GPA). I was able to revisit these hypotheses in my own work, and have been able to determine that the end of flowering in the model plant species Arabidopsis is not a global, synchronous event. Instead, the end of flowering occurs separately within each individual flowering branch (inflorescence), and requires new, seed-containing fruit to be present. Without these seed, arrest is delayed within this inflorescence. Working alongside our collaborators in the University of Nottingham, we have been able to show that auxin, a plant hormone, is exported from seeds, and it is this signal which brings about inflorescence arrest.
Expanding further on this work, I examined the production of flowers and properties of the inflorescence meristem. I used large populations of Arabidopsis and monitored them; randomised plants were selected and destructively sampled daily. Through this in-depth examination I have been able to show that the end of flowering in Arabidopsis is a flexible, two-stage process. First, the inflorescence meristem arrests, stopping the production of new floral primordia. After this, inflorescence arrest occurs when previously-produced floral buds stop developing and opening. We believed that the plant hormone cytokinin may be responsible for these effects, and as such examined cytokinin mutants. We have shown that a perceived increase in cytokinin availability is able to delay arrest in both inflorescence meristems and floral meristems. As such, we have been able to show that cytokinin is a key regulator of floral arrest, and arrest is controlled by both cytokinin and auxin availability.
Through this research, we have significantly increased the understanding of the end of flowering, and have identified mechanisms by which floral arrest occurs.
Exploitation Route We have identified multiple new opportunities and directions for research in this area which could have significant impact in the long-term on yield production in crops. As such, the outcomes of this project may be developed further by other researchers, with an ultimate goal of supporting the agricultural sector.
Sectors Agriculture, Food and Drink