The TaSOC1-TaVRN1 module integrates photoperiod and vernalization signals to regulate wheat flowering.

Wheat needs different durations of vernalization, which accelerates flowering by exposure to cold temperature, to ensure reproductive development at the optimum time, as that is critical for adaptability and high yield. TaVRN1 is the central flowering regulator in the vernalization pathway and encodes a MADS-box transcription factor (TF) that usually works by forming hetero- or homo-dimers. We previously identified that TaVRN1 bound to an MADS-box TF TaSOC1 whose orthologues are flowering activators in other plants. The specific function of TaSOC1 and the biological implication of its interaction with TaVRN1 remained unknown. Here, we demonstrated that TaSOC1 was a flowering repressor in the vernalization and photoperiod pathways by overexpression and knockout assays. We confirmed the physical interaction between TaSOC1 and TaVRN1 in wheat protoplasts and in planta, and further validated their genetic interplay. A Flowering Promoting Factor 1-like gene TaFPF1-2B was identified as a common downstream target of TaSOC1 and TaVRN1 through transcriptome and chromatin immunoprecipitation analyses. TaSOC1 competed with TaVRT2, another MADS-box flowering regulator, to bind to TaVRN1; their coding genes synergistically control TaFPF1-2B expression and flowering initiation in response to photoperiod and low temperature. We identified major haplotypes of TaSOC1 and found that TaSOC1-Hap1 conferred earlier flowering than TaSOC1-Hap2 and had been subjected to positive selection in wheat breeding. We also revealed that wheat SOC1 family members were important domestication loci and expanded by tandem and segmental duplication events. These findings offer new insights into the regulatory mechanism underlying flowering control along with useful genetic resources for wheat improvement.

TaVrt2, an SVP-like gene, cooperates with TaVrn1 to regulate vernalization-induced flowering in wheat.

TaVrn1, encoding a MADS-box transcription factor (TF), is the central regulator of wheat vernalization-induced flowering. Considering that the MADS-box TF usually works by forming hetero- or homodimers, we conducted yeast-two-hybrid screening and identified an SVP-like MADS-box protein TaVrt2 interacting with TaVrn1. However, the specific function of TaVrt2 and the biological implication of its interaction with TaVrn1 remained unknown. We validated the function of TaVrt2 and TaVrn1 by wheat transgenic experiments and their interaction through multiple protein-binding assays. Population genetic analysis also was used to display their interplay. Transcriptomic sequencing and chromatin immunoprecipitation assays were performed to identify their common targets. TaVrt2 and TaVrn1 are flowering promoters in the vernalization pathway and interact physically in vitro, in planta and in wheat cells. Additionally, TaVrt2 and TaVrn1 were significantly induced in leaves by vernalization, suggesting their spatio-temporal interaction during vernalization. Genetic analysis indicated that TaVrt2 and TaVrn1 had significant epistatic effects on flowering time. Furthermore, native TaVrn1 was up-regulated significantly in TaVrn1-OE (overexpression) and TaVrt2-OE lines. Moreover, TaVrt2 could bind with TaVrn1 promoter directly. A TaVrt2-mediated positive feedback loop of TaVrn1 during vernalization was proposed, providing additional understanding on the regulatory mechanism underlying vernalization-induced flowering.

Dosage effect genes modulate grain development in synthesized Triticum durum-Haynaldia villosa allohexaploid.

Polyploidization in plants often leads to increased cell size and grain size, which may be affected by the increased genome dosage and transcription abundance. The synthesized Triticum durum (AABB)-Haynaldia villosa (VV) amphiploid (AABBVV) has significantly increased grain size, especially grain length, than the tetraploid and diploid parents. To investigate how polyploidization affects grain development at the transcriptional level, we perform transcriptome analysis using the immature seeds of T. durum, H. villosa, and the amphiploid. The dosage effect genes are contributed more by differentially expressed genes from genome V of H. villosa. The dosage effect genes overrepresent grain development-related genes. Interestingly, the vernalization gene TaVRN1 is among the positive dosage effect genes in the T. durum‒H. villosa and T. turgidum‒Ae. tauschii amphiploids. The expression levels of TaVRN1 homologs are positively correlated with the grain size and weight. The TaVRN1-B1 or TaVRN1-D1 mutation shows delayed florescence, decreased cell size, grain size, and grain yield. These data indicate that dosage effect genes could be one of the important explanations for increased grain size by regulating grain development. The identification and functional validation of dosage effect genes may facilitate the finding of valuable genes for improving wheat yield.

The General Transcription Repressor TaDr1 Is Co-expressed With TaVrn1 and TaFT1 in Bread Wheat Under Drought.

The general transcription repressor, TaDr1 gene, was identified during screening of a wheat SNP database using the Amplifluor-like SNP marker KATU-W62. Together with two genes described earlier, TaDr1A and TaDr1B, they represent a set of three homeologous genes in the wheat genome. Under drought, the total expression profiles of all three genes varied between different bread wheat cultivars. Plants of four high-yielding cultivars exposed to drought showed a 2.0-2.4-fold increase in TaDr1 expression compared to controls. Less strong, but significant 1.3-1.8-fold up-regulation of the TaDr1 transcript levels was observed in four low-yielding cultivars. TaVrn1 and TaFT1, which controls the transition to flowering, revealed similar profiles of expression as TaDr1. Expression levels of all three genes were in good correlation with grain yields of evaluated cultivars growing in the field under water-limited conditions. The results could indicate the involvement of all three genes in the same regulatory pathway, where the general transcription repressor TaDr1 may control expression of TaVrn1 and TaFT1 and, consequently, flowering time. The strength of these genes expression can lead to phenological changes that affect plant productivity and hence explain differences in the adaptation of the examined wheat cultivars to the dry environment of Northern and Central Kazakhstan. The Amplifluor-like SNP marker KATU-W62 used in this work can be applied to the identification of wheat cultivars differing in alleles at the TaDr1 locus and in screening hybrids.