Loss of floral repressor function adapts rice to higher latitudes in Europe.
The capacity to discriminate variations in day length allows plants to align flowering with the most favourable season of the year. This capacity has been altered by artificial selection when cultivated varieties became adapted to environments different from those of initial domestication. Rice flowering is promoted by short days when HEADING DATE 1 (Hd1) and EARLY HEADING DATE 1 (Ehd1) induce the expression of florigenic proteins encoded by HEADING DATE 3a (Hd3a) and RICE FLOWERING LOCUS T 1 (RFT1). Repressors of flowering antagonize such induction under long days, maintaining vegetative growth and delaying flowering. To what extent artificial selection of long day repressor loci has contributed to expand rice cultivation to Europe is currently unclear. This study demonstrates that European varieties activate both Hd3a and RFT1 expression regardless of day length and their induction is caused by loss-of-function mutations at major long day floral repressors. However, their contribution to flowering time control varies between locations. Pyramiding of mutations is frequently observed in European germplasm, but single mutations are sufficient to adapt rice to flower at higher latitudes. Expression of Ehd1 is increased in varieties showing reduced or null Hd1 expression under natural long days, as well as in single hd1 mutants in isogenic backgrounds. These data indicate that loss of repressor genes has been a key strategy to expand rice cultivation to Europe, and that Ehd1 is a central node integrating floral repressive signals.
University of Milan, Department of Biosciences, Via Celoria 26, 20133 Milan, Italy.
Jorge
J
Gómez-Ariza
University of Milan, Department of Biosciences, Via Celoria 26, 20133 Milan, Italy University of Milan, Department of Agricultural and Environmental Sciences - Production, Landscape, Agroenergy, Via Celoria 2, 20133 Milan, Italy.
Francesca
F
Galbiati
University of Milan, Department of Biosciences, Via Celoria 26, 20133 Milan, Italy.
Daniela
D
Goretti
University of Milan, Department of Biosciences, Via Celoria 26, 20133 Milan, Italy.
Vittoria
V
Brambilla
University of Milan, Department of Biosciences, Via Celoria 26, 20133 Milan, Italy.
Roshi
R
Shrestha
University of Milan, Department of Biosciences, Via Celoria 26, 20133 Milan, Italy Current Address: Università Cattolica del Sacro Cuore, Via Emiliana Parmense 84, Piacenza, Italy.
Andrea
A
Pappolla
CIRAD, UMR AGAP, Avenue Agropolis, 34398 Montpellier Cedex 5, France.
Brigitte
B
Courtois
University of Milan, Department of Biosciences, Via Celoria 26, 20133 Milan, Italy fabio.fornara@unimi.it.
Fabio
F
Fornara
D000222:Adaptation, Physiological; D000483:Alleles; D002874:Chromosome Mapping; D004777:Environment; D005060:Europe; D035264:Flowers / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant; D005838:Genotype; D012275:Oryza / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D017440:Photoperiod; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity
D010940:Plant Proteins; D012097:Repressor Proteins
Adaptation; Ehd1; Hd1; Hd3a; RFT1.; heading date; photoperiodic flowering; rice