IAP2-23-086

Flax forever: the possibility of immortality in the meristems of an annual plant

Plants are sessile organisms, and so are highly exposed to environmental variability. In response, their developmental progress is highly flexible. For example, many plants can transition to a reproductive stage and revert to vegetativeness multiply within one life span; a polycarpic, perennial habit. Many plant lineages that are largely perennial nevertheless contain annual species. These evolutionary switches in life history are profound, changing the pattern of resource allocation and fitness strategies for the species. For ecological communities, the implicated differences in plant survival and stress response are also significant. However, the environmental drivers and genetic regulators of these different evolutionary strategies are not well explored (1).
At the morphological level, perennialism is often achieved by spatially variable transition to flowering. In “annual” species all active meristems become committed to flowering and the plant subsequently dies (monocarpy). In polycarpic plants, a subset of meristems are maintained in vegetative or dormant state for indeterminate growth after flowering (1). The genetic control of perennialism is thus thought to be intricately linked to that of flowering and dormancy, both environmentally-controlled traits (2).
Few species include both annual and perennial populations, a case that has been reported in the field for pale flax, Linum bienne, although not yet observed in laboratory conditions (3,4). This project aims to use Linum bienne as a case study for the regulation and environmental response of the annual versus perennial habit. The project will characterise the life history and morphology of L. bienne accessions from different latitudes in the glasshouse and field, correlate environmental drivers to behavioural change, and identify potential candidate genes underlying variation in life history.

The methodologies employed will exploit the expertise of the three collaborating research groups: Dr Hepworth will provide training in molecular genetic control of flowering in response to climate; Dr Sanderson’s expertise is in temporal-spatial modelling and interactions between environment and organism life histories; Dr Brennan is an expert on the genetics, trait evolution and ecology of wild flowers.
Dr Hepworth will oversee controlled environment and common garden experiments investigating developmental progression in response to temperature and field conditions (5).
Dr Brennan will provide flax-specific knowledge, germplasm and genetic resources, including a diversity panel (4). Dr Brennan will guide repeated fieldwork to monitor plant behaviour over multiple years to test the core hypothesis that L. bienne shows perennial phenotypes in the field.
Dr Sanderson will supervise the use of statistical modelling techniques (for example, 6) to link experimental manipulations to field observations across spatial scales, to identify potential drivers of perenniality in the field.

Year 1

The student will grow an existing Linum bienne collection from across Europe (4), including several accessions identified as long-life, putative field-perennials, alongside two well-characterised sequenced annuals. The collection will be characterised to identify the pattern of meristems converting to inflorescences, reverting to vegetative fate, or being retained as dormant or vegetative. The student will test the different lines in controlled conditions with and without exposure to winter-like cold (vernalisation) and different photoperiods, to see how this modifies commitment to floral fate of the different meristems. Reproductive potential will be measured via seed production, to estimate resource allocation and fitness.
In parallel, the student will conduct a common garden experiment at Durham Botanic Garden, using the same collection, to compare how life history, architecture and reproductive potential of plants differs in the field. The behaviour of plants surviving beyond one year will be monitored over the next 2 years.
In the summer of the first year, the student will visit field sites identified by Dr Brennan to note the morphology and flowering behaviour of L. bienne plants in natura.

Year 2

The student will use anatomic and life history data gathered in the first year to start statistical analysis of the growth characteristics of the plants and their link to climate-of-origin data, to generate hypotheses for laboratory testing (e.g. relationships to precipitation would be tested by comparing watering regimes in the controlled environment).
The student will choose a single long-lived accession to compare with an annual accession for which genome sequence is available. Based on the previous experiments, the student will identify suitable conditions and time points to compare transcriptomes between the accessions to maximise differences in the fate of their meristems. The student will then identify potential regulators of flowering and perennial fate based on known actors in flowering, annual dormancy and vernalisation response in perennial Populus (poplar) and Malus (apple; like Linum also in the rosid clade) and well characterised perennial/annual Arabis/Arabidopsis species (2), as well as existing knowledge of close relative Linum usitatissimum flowering regulators (7–9). These will include the PEBP, MADS-BOX and TCP families of transcription factors (1).
The student will continue the common garden experiment where plants persist from Year 1.
In the summer of the second year, the student will visit field sites again to identify L. bienne plants surviving for multiple years, and note their morphology and flowering behaviour, and take samples for DNA extraction.

Year 3

The student will Sanger sequence selected candidate genes across the panel of accessions and field samples, generate haplotype clusters that could link to transcriptional and functional differences (5), and compare these to climate-of-origin indicators (temperature, precipitation, etc) to identify climatic drivers for perennialism.
The common garden experiment will continue.
In the spring-summer, the student will conduct field visits to annual and long-lifed Linum populations and monitor their reproductive success.
The student will synthesis the collected data using GLS and mixed-models to generate predictions for field behaviour and causative genes across climates. Depending on conference timing, the student will attend an international conference in this year to present their results.

Year 3.5

Statistical modelling will be concluded as the student compiles their thesis and prepares publications.

This project will provide the student with comprehensive practical and theoretical training in evolutionary plant biology, from field observation and common garden experimentation to molecular biology techniques, transcriptomics, and mathematical analysis, ideal for future biology jobs. The bioinformatics and statistical modelling training will be highly transferable to a range of scientific or commercial data acquisition and analysis roles.