Wheat EARLY FLOWERING3 is a dawn-expressed circadian oscillator component that regulates heading date

Abstract

Using an eight-parent Multiparent Advanced Generation Inter-Cross (MAGIC) population we investigated how variation at circadian clock-associated genes contributes to the regulation of heading date in UK and European winter wheat varieties. We identified homoeologues of EARLY FLOWERING 3 (ELF3) as candidates for the Earliness per se (Eps) D1 and B1 loci in field conditions. We confirmed that a SNP within the coding region of TaELF3-B1 is a candidate polymorphism underlying the Eps-B1 locus. We found that a reported deletion at the Eps-D1 locus encompassing TaELF3-D1, is instead a novel allele that lies within an introgression region containing an inversion relative to the Chinese Spring D genome. Using T. turgidum cv. Kronos carrying loss of function alleles of TtELF3 we show that ELF3 does regulate heading by demonstrating that the loss of a single ELF3 homoeologue was sufficient to alter heading date. These studies demonstrated that ELF3 forms part of the circadian oscillator but loss of all homoeologues was required to affect circadian rhythms. Similarly, loss of functional LUX ARRHYTHMO (LUX) in T. aestivum, an orthologue of a protein partner of Arabidopsis ELF3, severely disrupted circadian rhythms. ELF3 and LUX transcripts are not co-expressed at dusk suggesting the structure of the wheat circadian oscillator might differ to that of Arabidopsis. Our demonstration that alteration to ELF3 homoeologues can affect heading date separate from effects on the circadian oscillator suggests a role for ELF3 in cereal photoperiodic responses that could be selected for, without pleiotropic deleterious alterations to circadian rhythms.