Earliness Per Se by Temperature Interaction on Wheat Development.

Differences in time to heading that remain after photoperiod and vernalisation requirements have been saturated are classified as earliness per se (Eps) effects. It has been commonly assumed that Eps genes are purely constitutive and independent of environment, although the likely effect of temperature on Eps effects in hexaploid wheat has never been tested. We grew four near isogenic lines (NILs) for the Eps gene located in chromosome 1D (Eps-D1) at 6, 9, 12, 15, 18, 21 and 24 °C. In line with expectations we found that lines carrying the Eps-late allele were always later than those with Eps-early alleles. But in addition, we reported for the first time that the magnitude of the effect increased with decreasing temperature: an Eps x temperature interaction in hexaploid wheat. Variation in heading time due to Eps x temperature was associated with an increase in sensitivity to temperature mainly during late reproductive phase. Moreover, we showed that Eps alleles exhibited differences in cardinal (base, optimum, maximum) temperatures and that the expression of ELF3, (the likely candidate for Eps-D1) also interacted with temperature.

The identification of new candidate genes Triticum aestivum FLOWERING LOCUS T3-B1 (TaFT3-B1) and TARGET OF EAT1 (TaTOE1-B1) controlling the short-day photoperiod response in bread wheat.

Perception of photoperiod changes enables plants to flower under optimum conditions for survival. We used doubled haploid populations of crosses among Avalon × Cadenza, Charger × Badger and Spark × Rialto and identified short-day flowering time response quantitative trait loci (QTL) on wheat chromosomes 1BS and 1BL. We used synteny between Brachypodium distachyon and wheat to identify potential candidates for both QTL. The 1BL QTL peak coincided with TaFT3-B1, a homologue of the barley gene HvFT3, the most likely candidate gene. The 1BS QTL peak coincided with homologues of Arabidopsis thaliana SENSITIVITY TO RED LIGHT REDUCED 1, WUSCHEL-like and RAP2.7, which is also known as Zea mays TARGET OF EAT1, named TaSRR1-B1, TaWUSCHELL-B1 and TaTOE1-B1, respectively. Gene expression assays suggest that TaTOE1-B1 and TaFT3-B1 are expressed more during short days. We identified four alleles of TaFT3-B1 and three alleles of TaTOE1-B1. We studied the effect of these alleles in the Watkins and GEDIFLUX diversity panels by using 936 and 431 accessions, respectively. Loss of TaFT3-B1 by deletion was associated with late flowering. Increased TaFT3-B1 copy number was associated with early flowering, suggesting that TaFT3-B1 promotes flowering. Significant association was observed in the GEDIFLUX collection for TaTOE1-B1, a putative flowering repressor.

Delimitation of the Earliness per se D1 (Eps-D1) flowering gene to a subtelomeric chromosomal deletion in bread wheat (Triticum aestivum).

Earliness per se (Eps) genes account for the variation in flowering time when vernalization and photoperiod requirements are satisfied. Genomics and bioinformatics approaches were used to describe allelic variation for 40 Triticum aestivum genes predicted, by synteny with Brachypodium distachyon, to be in the 1DL Eps region. Re-sequencing 1DL genes revealed that varieties carrying early heading alleles at this locus, Spark and Cadenza, carry a subtelomeric deletion including several genes. The equivalent region in Rialto and Avalon is intact. A bimodal distribution in the segregating Spark X Rialto single seed descent (SSD) populations enabled the 1DL QTL to be defined as a discrete Mendelian factor, which we named Eps-D1. Near isogenic lines (NILs) and NIL derived key recombinants between markers flanking Eps-D1 suggest that the 1DL deletion contains the gene(s) underlying Eps-D1. The deletion spans the equivalent of the Triticum monoccocum Eps-A (m) 1 locus, and hence includes MODIFIER OF TRANSCRIPTION 1 (MOT1) and FTSH PROTEASE 4 (FTSH4), the candidates for Eps-A (m) 1. The deletion also contains T. aestivum EARLY FLOWERING 3-D1 (TaELF3-D1) a homologue of the Arabidopsis thaliana circadian clock gene EARLY FLOWERING 3. Eps-D1 is possibly a homologue of Eps-B1 on chromosome 1BL. NILs carrying the Eps-D1 deletion have significantly reduced total TaELF3 expression and altered TaGIGANTEA (TaGI) expression compared with wild type. Altered TaGI expression is consistent with an ELF3 mutant, hence we propose TaELF3-D1 as the more likely candidate for Eps-D1. This is the first direct fine mapping of Eps effect in bread wheat.

Validation of a 1DL earliness per se (eps) flowering QTL in bread wheat (Triticum aestivum).

Vernalization, photoperiod and the relatively poorly defined earliness per se (eps) genes regulate flowering in plants. We report here the validation of a major eps quantitative trait locus (QTL) located on wheat 1DL using near isogenic lines (NILs). We used four independent pairs of NILs derived from a cross between Spark and Rialto winter wheat varieties, grown in both the field and controlled environments. NILs carrying the Spark allele, defined by QTL flanking markers Xgdm111 and Xbarc62, consistently flowered 3-5 days earlier when fully vernalized relative to those with the Rialto. The effect was independent of photoperiod under field conditions, short days (10-h light), long days (16-h light) and very long days (20-h light). These results validate our original QTL identified using doubled haploid (DH) populations. This QTL represents variation maintained in elite north-western European winter wheat germplasm. The two DH lines used to develop the NILs, SR9 and SR23 enabled us to define the location of the 1DL QTL downstream of marker Xgdm111. SR9 has the Spark 1DL arm while SR23 has a recombinant 1DL arm with the Spark allele from Xgdm111 to the distal end. Our work suggests that marker assisted selection of eps effects is feasible and useful even before the genes are cloned. This means eps genes can be defined and positionally cloned in the same way as the photoperiod and vernalization genes have been. This validation study is a first step towards fine mapping and eventually cloning the gene directly in hexaploid wheat.

Copy number variation affecting the Photoperiod-B1 and Vernalization-A1 genes is associated with altered flowering time in wheat (Triticum aestivum).

The timing of flowering during the year is an important adaptive character affecting reproductive success in plants and is critical to crop yield. Flowering time has been extensively manipulated in crops such as wheat (Triticum aestivum L.) during domestication, and this enables them to grow productively in a wide range of environments. Several major genes controlling flowering time have been identified in wheat with mutant alleles having sequence changes such as insertions, deletions or point mutations. We investigated genetic variants in commercial varieties of wheat that regulate flowering by altering photoperiod response (Ppd-B1 alleles) or vernalization requirement (Vrn-A1 alleles) and for which no candidate mutation was found within the gene sequence. Genetic and genomic approaches showed that in both cases alleles conferring altered flowering time had an increased copy number of the gene and altered gene expression. Alleles with an increased copy number of Ppd-B1 confer an early flowering day neutral phenotype and have arisen independently at least twice. Plants with an increased copy number of Vrn-A1 have an increased requirement for vernalization so that longer periods of cold are required to potentiate flowering. The results suggest that copy number variation (CNV) plays a significant role in wheat adaptation.