Award details

Evolution of floral organ reduction

Reference	BB/H01313X/1
Principal Investigator / Supervisor	Dr Angela Hay
Co-Investigators / Co-Supervisors
Institution	University of Oxford
Department	Plant Sciences
Funding type	Research
Value (£)	429,776
Status	Completed
Type	Research Grant
Start date	01/10/2010
End date	28/02/2013
Duration	29 months

Abstract

This project aims to understand the genetic control of petal number reduction in Cardamine hirsuta. Comparison with its close relative, the model organism Arabidopsis thaliana, which represents the ancestral state for petal number in the Brassicaceae, allows us to investigate the evolution of this developmental process. This change in morphology may have evolved in association with increased selfing, consistent with petal loss in cleistogamous flowers of Cardamine kokaiensis. We will characterise natural and induced variation to understand the genetic control of petal reduction in C. hirsuta. LEAFY (LFY), which encodes an important regulator of petal development, maps to a large effect QTL controlling petal number in C. hirsuta. We will confirm whether LFY underlies this QTL by transgenic analysis of parental alleles in lfy mutants, and fine-map the QTL in near isogenic lines to identify the responsible gene in the case that it is not LFY. Four petal mutants that convert C. hirsuta to A. thaliana petal number will be characterised and the underlying genes identified as these likely represent a repressive input that is species-specific into the genetic network regulating petal number. Mutant analyses also suggest that LFY-independent activation of the key petal regulator APETALA1 (AP1) has been lost in C. hirsuta when compared with A. thaliana. We will use transgenic analysis and genetics to investigate cis-regulatory evolution of the AP1 gene and its phenotypic consequences. This work will therefore enhance our understanding of the molecular changes underpinning population and species diversification.

Summary

We aim to understand how different species evolve different physical features. Flowering plants have the greatest species number and diversity of any plant group on earth and petals played a critical role in generating this diversity by attracting different pollinators. Many plants can also pollinate themselves and this can be advantageous for weeds like hairy bittercress that invade new habitats. This transition to self-pollination can be associated with petal loss, however, the genetic mechanisms that determine petal number, and how these have varied during evolution, are poorly understood and are hence the focus of our research. Our research aims to understand the genetic changes that underlie changes in petal number between two mustard species, the model organism thale cress (Arabidopsis thaliana) and hairy bittercress (Cardamine hirsuta). These species are closely related and easy to work with in the lab, so genetic and transgenic experiments can be used to identify mechanisms that make these two species look different from each other. Thale cress has a typical mustard flower with four petals while hairy bittercress differs by having fewer petals. We know that one region of the hairy bittercress genome controls a large amount of the variation observed in petal number in this species. We also know that an important gene controlling petal development called LEAFY maps to this genomic region. In order to identify genes that repress petal number in hairy bittercress we induced variation in the genome by mutagenesis and identified mutants that convert hairy bittercress to thale cress petal number. Identifying the genes mutated in these plants will tell us which genes act to reduce petal number in hairy bittercress but not in thale cress. One way that LEAFY regulates petal development is by turning on expression of the APETALA1 gene. Other regulators in thale cress but not in hairy bittercress also turn on this gene. We want to know whether this difference in generegulation plays a part in making these two species look different from each other. Here, we will determine whether LEAFY or a different gene controls the variation observed in hairy bittercress populations. We will also identify genes that act only in hairy bittercress to reduce petal number. Many of the genetic changes during evolution that produce different-looking species result from changes in the way genes are regulated and we will test whether this is true for the APETALA1 gene in these two mustard species. Thus, species-specific differences in petal number between hairy bittercress and thale cress, and natural variation in this trait between hairy bittercress populations around the world, provide an exciting experimental platform to trace evolution from specific changes in gene regulation through to altered morphologies in nature. Another group of mustards called Brassicas are remarkable for containing more important agricultural and horticultural crops than any other plant genus. Understanding the genetic basis of mustard diversity is therefore a vital part of generating crops for the 21st century.

Impact Summary

Potential beneficiaries of this research: i. General public ii. Schools iii. Brassica community including breeders How will they benefit from this research and what will be done to ensure that they do? i. The general public will benefit from this research project that taps a genuine interest in understanding the natural world. Investigating the evolution of petal reduction in the selfing mustard species Cardamine hirsuta will provide a concrete example of which genes were altered during evolution to produce flowers that look different. This project also highlights for discussion two current societal issues regarding mustard pollination, namely the potential spread of transgenes from GM Brassica crops to non-GM Brassicas by pollinators, and the impact of a decline in the British honeybee population, which are the primary pollinators of oilseed Brassica crops. I will ensure that my research is communicated to the public via press release, College open days and open lectures, and informal discussions with interest groups. Additionally, this project will provide training for two research staff in an extensive range of genetic methodologies and translational skills that can subsequently be brought to the UK public or private sector. ii. School students and teachers will benefit from this genetics project aimed at understanding the relationship between petal number and pollination strategies in mustard species. It has relevance to their interest in biodiversity and genetics and lets them make connections between plants and pollinators and the implications of this process for GM crops and insect populations. I will continue to work together with the Secondary Education Officer for the Oxford University Museum of Natural History and Botanic Gardens to engage with schools. iii. The information developed here should contribute to building a sound knowledge base of crucifer petal development and how it can be modified through evolution, which could ultimatelyinform Brassica crop improvement. Furthermore, a series of lasting genetic resources will be generated during this project (NILs, HIFs, transgenic lines, mutants, genetic markers and genotype data) that could be used for future study of other traits of agronomic interest. I will ensure that these issues will be flagged in presentations (e.g annual Brassica Research Community meeting; Oilseed Rape Genetic Improvement Network meeting), on the lab website and via the university technology transfer company ISIS innovation.

Committee	Research Committee B (Plants, microbes, food & sustainability)
Research Topics	Plant Science
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

Associated awards:

BB/H01313X/2 Evolution of floral organ reduction

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