The genetic and molecular architecture controlling flowering time in interaction with the environment in winter wheat

Abstract

The time of flowering is a key factor for global adaptability to diverse conditions and a critical agronomical factor for successful reproduction. This high potential is resulting from a natural variation that has remained largely unexplored so far. For this reason, the present research endeavors to decrypt the genetic and molecular architecture of flowering time regulation in winter wheat in interaction with the environment. We used a diverse collection set made of 213 elite bread wheat cultivars from Germany, central Europe, and other countries. Three complementary studies were conducted:<br /> The first study evinced through the phenotypic evaluation, that the genotypic response to climatic parameters variation depending on location and year revealed that the spring temperature dominates other climatic stimuli in reducing the number of days to heading in low and middle latitudes, while the very low yearly thermal change uncovered the implication of photoperiod in promoting heading in the higher ones. The solar radiation is mostly delaying flowering time, whereas the precipitations showed locations and seasonal depending effect on heading date.<br /> The outcomes of the second study showed out of the screening of all cultivars for the known vernalization and photoperiod genes that the allele combination vrn-1/Vrn-2/Ppd-D1b is responsible for winter growth habit in 95% of the adapted cultivars. QTL × environments analysis detected a novel locus TaHd102 on chromosome 5A, which is stable across all environments and explains 13.8% of the genetic variance. The allelic variation at TaHd102 alters flowering time by 1.2 days. Including the non-adapted cultivars in the analysis, an exotic allele at QTL TaHd044 on chromosome 3A could be identified. The latter explains up to 33% of the genetic variance and has an allele effect of 5.6 days. The genetic response to climatic stimuli selects thermo-sensitive and circadian clock loci in the lower and higher latitudes, respectively for inducing heading. A novel locus TaHd098 located on the small arm of chromosome 5A, which showed multiple epistatic interactions with 15 known regulators of flowering time was uncovered.<br /> In the third study, QTL mapping provided by the previous genetic analysis was combined with transcriptomics. The early flowering cultivar “Kontrast” and the late flowering one “Basalt”, developed in Germany, were selected for this analysis. 664 and 1075 differentially expressed genes in Kontrast” compared to “Basalt” in the apex and leaves respectively, could be identified in 23 QTL intervals for heading date. In transition apex, Histone H3-K36 methylation and regulation of circadian rhythm are both controlled by the same homoeologous genes/QTL TaHd112, TaHd124, and TaHd137. In the double ridge stage, the gene FLOWERING TIME LOCUS T located on chromosome 7D acts as a flowering repressor due to polymorphisms in the coding sequence. The wheat orthologous of the transcription factor ASYMMETRIC LEAVES 1 (AS1), mapped in TaHd102 is uncovered in the late reproductive stage. In its promoter region, AS1 exhibits a deletion of eight single nucleotides in the binding site of the SUPPRESSOR OF CONSTANS OVEREXPRESSION 1 (SOC1) gene. Both genes induce flowering time in response to Gibberellin biosynthesis in Arabidopsis thaliana background.