WheatEARLY FLOWERING3is a dawn-expressed circadian oscillator component that regulates heading date

Abstract

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.

EARLY FLOWERING 3interactions withPHYTOCHROME BandPHOTOPERIOD1are critical for the photoperiodic regulation of wheat heading time

“…In barley and wheat, loss-of-function mutations in ELF3 [26,27,30] or LUX [31][32][33] result in very early heading under both LD and SD conditions, suggesting that in these species the EC is critical for the photoperiodic response. Natural allelic variation at ELF3 has also been associated with differences in heading time in diploid Triticum monococcum and in hexaploid wheat [26,34,35].…”

Circadian regulation of the transcriptome in a complex polyploid crop

“…Five wheat transcripts with homology to Arabidopsis ELF4 and ELF4-L1-4 accumulated with a mean circadian phase of 12.6 h, similar to ELF4 , but with lower relative amplitudes (Figs 3J and 3K and S17 ). TaELF3-1D has previously been found to underlie the Eps-D1 QTL in wheat variety Cadenza [ 18 , 19 ] which is likely to be due to an introgression on chromosome 1D [ 44 ]. Eps-D1 is associated with earlier flowering under long days in wheat, particularly under warm temperatures [ 45 ].…”

“…A previously described telomeric introgression on chromosome 1D contains an introgressed Ta ELF3 orthologue [ 44 ]. To account for mapping bias and accurately characterise the expression of this gene ( Fig 3L ), filtered and trimmed mRNA reads were aligned as above but to a pseudo reference constructed by concatenating Chinese Spring RefSeq v1.0 to the well-defined 1D introgression extracted from the Jagger genome assembly [ 102 ].…”

Overexpression of the WAPO-A1 gene increases the number of spikelets per spike in bread wheat

“…Within the 4-parent CSIRO population alleles at the Ppd-D1 , PPD-B1 , VRN-A1 , VRN-B1 and VRN-D1 loci are segregating in addition to WAPO-A1 and WAPO-B1 32 , 35 . In addition to WAPO-A1 and WAPO-B1, within the 8-parent NIAB population Ppd-D1 , ELF3-B1 and ELF3-D1 are also segregating 4 , 7 , 28 , 50 . All of these loci were identified as significant SPS QTL in the respective populations with the exception of ELF3-B1 and ELF3-D1, which may be due to their minor effect on SPS or due to more complex environmental interactions of ELF3 51 .…”