HEMOTIONAL

HEteroblasty MOdelling: the TImetable of ONtogeny in Arabidopsis Leaves

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 Obiettivo del progetto (Objective)

'The diversity of forms in nature raises questions on the mechanisms by which these forms originate. In many plant species, variations in leaf shape and size between juvenile and adult leaves accompany the acquisition of reproductive competence. This is termed heteroblasty. The canonical molecular pathway controlling heteroblasty has been recently described. It is topped by miR156, a miRNA which acts as a master switch to prevent the adult behaviour through the repression of transcription factors. However, the way how these genes control the growth patterns by which heteroblastic forms arise remains unknown. In this project, I propose to study the dynamics of heteroblasty establishment in Arabidopsis, by combining the knowledge acquired in molecular biology on the control of heteroblasty with the expertise on modelling of leaf growth in the host group (Prof. Enrico Coen and Prof. Andrew Bangham). Preliminary results suggest that the heteroblastic changes in leaf shape are ruled by the miR156 pathway until a certain leaf developmental stage, while the changes in leaf size are conditional on plant’s capacity to exploit its environmental resources. To test this hypothesis, I will i) use a modelling platform developed in the host group to compare quantitatively the early growth pattern of leaf 6 (adult) with the one of leaf 1 (juvenile), ii) develop an inducible line to analyze and model the spatiotemporal effects of the miR156 pathway in these early growth patterns, iii) modify the environment during leaf 6 development to analyze the plasticity of this leaf, and iv) analyze and disturb the expression of miR156 during leaf 6 development to question the involvement of the miR156 pathway in the control of final shape and size of this leaf. Through a combination of developmental, physiological and modelling approaches, this integrative analysis of heteroblasty will generate fundamental knowledge on leaf growth, a key target for breeding robust crops within a changing world.'

Introduzione (Teaser)

An EU-funded project has made progress in determining the genetic and environmental input in development of leaf shape and size.

Descrizione progetto (Article)

When a seed first germinates the first leaves are juvenile and are a different shape to their adult successors. This phenomenon is called heteroblasty. Genetic and environmental control of heteroblasty is important as the shape and position of a leaf dictates how good it is at producing carbohydrates.

The 'Heteroblasty modelling: The timetable of ontogeny in Arabidopsis leaves' (HEMOTIONAL) project has investigated the genetic and environmental control of both leaf shape and size. The scientists did this by comparing models of development for the first leaf with that of leaf six in the model plant thale cress, Arabidopsis.

Using an Arabidopsis model, the team gained data that supports the theory that growth slows over the whole leaf via a single global growth inhibitor that increases with time. The scientists also developed software to investigate the growth as well as cell division. The data do not show a direct relationship between rate of cell division and growth, but do suggest they are controlled by the same set of morphogens.

HEMOTIONAL also investigated how genes involved in heteroblasty are able to modulate growth. A time-lapse microscopy platform was set up using fluorophores that mark cell outlines or indeed any gene of interest that turns on after heat shock induction. The construct is still being tested and validated.

As Arabidopsis plants grown in agar are much smaller than their counterparts in soil, the team also looked at the effects of changing environmental conditions. Agar plants showed reduced heteroblasty. By transferring plants from agar to soil at different stages of development, the scientists showed that heteroblastic variations in leaf change are fixed early in leaf development. Leaf size, however, is affected by environmental changes.

Results from HEMOTIONAL present an opportunity to address the global challenge of food security. Leaf development and growth are key areas in addressing the worldwide food shortage and may also be used to forecast the mitigating effects of plant growth on climate change.