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What makes plants produce flowers?

Flowering time can vary considerably in maize, impacting the architecture of the plant and also its agricultural value, for example in terms of productivity and yield. INRA researchers in Versailles-Grignon have shown that this variation involves a region on chromosome 6 of maize.

Irrigation de maïs.. © INRA, DAMOUR Léon-Louis
Updated on 06/03/2015
Published on 10/22/2012

In plants such as maize, stems and leaves stop forming when the reproductive organs in the flower are initiated: this is referred to as floral transition. As a result, the number of leaves no longer changes and the plant pursues its growth until flowering. Floral transition governs the number of leaves, influences the height and flowering time of the plant and contributes partially to its selective value (e.g. grain number and weight). In practice, the flowering time in maize ranges from 35 to 120 days after sowing, and more than 60 genomic regions are involved in its determinism.

INRA researchers in Versailles-Grignon and their colleagues at Université Paris-Sud and CNRS have focused on the determination of flowering time in maize. Using a batch of commercial seeds, and thanks to successive crossings performed over 11 generations, they first of all selected plants displaying early, late or very late flowering. The very late flowering plants were distinctive for their delayed floral transition, their production of an additional leaf and their greater height.

The scientists then identified a region on chromosome 6 displaying marked sequence and structural variations and containing a supplementary element. This element, the eIF-4A initiation factor, forms part of a family of genes which includes members that are involved in the growth, development and flowering time of the model plant Arabidopsis thaliana.

An analysis of 317 maize lines of different geographical origins confirmed the role of this chromosomal region in variations in the flowering time, leaf number and height of plants. However, analysis of the impact of genetic variability in this region on these different traits was dependent on the geographical origin of the lines. The genomic advances thus achieved mean it is now possible to find hundreds of genomic regions that are involved in the variation of a quantitative trait. Nevertheless, the sum of individual effects in each region can generally only explain a small part of overall genetic variability. The hypotheses suggested to explain this so-called "missing" heritability include the existence of numerous, unidentified genetic variants, interactions between genes (epistasis) or the involvement of epigenetic variants; i.e. not linked to a change in the DNA sequence.

In addition to its usefulness to plant breeding, these findings show that the complexity of interactions between genes is implicated in the hereditary trait of flowering time in maize, and throw new light on the paradox referred to as missing heritability.

Reference

Durand E., Bouchet S., Bertin P., Ressayre A., Jamin P., Charcosset A., Dillmann C. and Tenaillon M.I. 2012. Flowering Time in Maize: Linkage and Epistasis at a Major Effect Locus. Genetics 190: 1547.