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

Optimising the seasonal control of flowering in the major crops is an important component of breeding to match crop adaptation to the target environment. Using an eight parent Multiparent Advanced Generation Inter-Cross (MAGIC) population we investigated the contribution of variation at circadian clock-associated genes to the regulation of heading date (flowering) in UK and European winter wheat varieties. We identified homoeologues of EARLY FLOWERING 3 (ELF3) as candidate genes 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 the likely causal polymorphism underlying the Eps-B1 locus. We also identified that a reported deletion at the Eps-D1 locus encompassing TaELF3-D1, is in fact a novel allele that lies within an introgression region that contains an inversion relative to the Chinese Spring D genome. Our findings that ELF3 might be associated with the regulation of heading date prompted us to investigate whether ELF3 is a circadian oscillator gene in wheat, as it is in Arabidopsis. Using T. turgidum cv. Kronos carrying loss of function alleles for both copies of TtELF3 we found that circadian rhythms were severely disrupted. Furthermore, in T. aestivum, we found that loss of functional LUX ARRHYTHMO (LUX), an orthologue of the protein partner of ELF3 in Arabidopsis, also severely disrupted circadian rhythms. Whilst these data suggest a function for both ELF3 and LUX in the wheat circadian oscillator, that oscillator might be structured differently to that of Arabidopsis because wheat ELF3 and LUX transcripts are maximal at the end of the night and day respectively, rather than co-expressed at dusk as they are in Arabidopsis. We conclude that there is sufficient allelic diversity within the three wheat ELF3 homoeologues for selection to delay or advance heading, and that this can be achieved without pleiotropic deleterious alterations to circadian rhythms.