Ectopic Expression of Triticum polonicum VRT-A2 Underlies Elongated Glumes and Grains in Hexaploid Wheat in a Dosage-Dependent Manner

Flower development is an important determinant of grain yield in crops. In wheat (Triticum spp.), natural variation for the size of spikelet and floral organs is particularly evident in Triticum turgidum ssp. polonicum (also termed Triticum polonicum), a tetraploid subspecies of wheat with long glumes, lemmas, and grains. Using map-based cloning, we identified VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (VRT2), which encodes a MADS-box transcription factor belonging to the SHORT VEGETATIVE PHASE family, as the gene underlying the T. polonicum long-glume (P1) locus. The causal P1 mutation is a sequence rearrangement in intron-1 that results in ectopic expression of the T. polonicum VRT-A2 allele. Based on allelic variation studies, we propose that the intron-1 mutation in VRT-A2 is the unique T. polonicum subspecies-defining polymorphism, which was later introduced into hexaploid wheat via natural hybridizations. Near-isogenic lines differing for the P1 locus revealed a gradient effect of P1 across spikelets and within florets. Transgenic lines of hexaploid wheat carrying the T. polonicum VRT-A2 allele show that expression levels of VRT-A2 are highly correlated with spike, glume, grain, and floral organ length. These results highlight how changes in expression profiles, through variation in cis-regulation, can affect agronomic traits in a dosage-dependent manner in polyploid crops.

Analysis of gliadin patterns and diversity in Triticum polonicum L. accessions from Ethiopia

<p>Gliadins from 25 accessions represented by 350 individual seed samples were analysed by acid-polyacrylamide gel electrophoresis (A-PAGE) with the objective of identifying gliadin band patterns and examine the extent of diversity in <em>Triticum polonicum </em>L. collections from Ethiopia. Seventy polymorphic bands and 68 different patterns were identified. Eighteen different mobility bands and 16 patterns were identified in <em>ω</em>-gliadin region, 22 bands and 20 patterns in <em>γ-</em>gliadin region, 12 bands and 22 patterns in <em>β-</em>gliadin region and 18 bands and 10 patterns in <em>α</em>-gliadin region. The average genetic diversity calculated from the data of the four gliadin zones of the analysed samples was 0.15. The γ region have the highest diversity (H = 0.193), followed by ω regions (H = 0.177) and β region (H = 0.168) and the lowest diversity was observed in α region (H = 0.127). Cluster analysis based on genetic distances resulted in grouping of the analysed accessions in to seven main groups. Though the level of diversity was relatively lower than other tetraploid wheat species from Ethiopia, the findings are indicative of the existence of variation in the collections which can be exploited for wheat improvement.</p>

TpIRT1 is a transition metal transporter in Polish Wheat (Triticum polonicum L.) with a broad substrate specificity

Aims (1) Explore the metal substrate specificity of homologous TpIRT1A and TpIRT1B transporters from dwarf Polish wheat by expressing them in protoplast, yeast, and transgenic Arabidopsis; (2) screen polymorphic residues of IRT1 homologs from tetraploid and diploid ancestral wheat species that change the substrate specificity.Methods Two IRT1 homoeologs were isolated from A (TpIRT1A) and B (TpIRT1B) genomes of a tetraploid crop, polish wheat (Triticum polonicum). Both of them were analysed by expressing them in yeast and Arabidopsis protoplast, respectively. Then we constructed over-expressing transgenic plants of TpIRT1B for metals property analysis in Arabidopsis. We also isolated 22 IRT1 homoeologs from tetraploid and diploid ancestral wheat species and expressed them in yeast for function analysis. Results Our data highlighted the importance of TpIRT1 in the uptake and translocation of Fe, Mn, Co, and Cd with direct implications for wheat yield potential. Both TpIRT1A and TpIRT1B were located at the plasma membrane and internal vesicles in Arabidopsis protoplasts, and responsible for Cd and Co sensitivity in yeast. The over-expression of TpIRT1B in A. thaliana increased Fe, Mn, Co, and Cd concentration in its tissues and improved plant growth under Fe, Mn, and Co deficiencies, while causing more sensitivity to Cd than wild-type plant. Functional analysis of IRT1 homoeologs from tetraploid and diploid ancestral wheat species in yeast disclosed four distinct amino acid residues in TdiIRT1B (T. dicoccum) and TtuIRT1B (T. turgidum). Altogether, these results increase the knowledge of IRT1 function in a global crop, wheat.

The semi-dwarfing gene Rht-dp from dwarf polish wheat (Triticum polonicum L.) is the "Green Revolution” gene Rht-B1b

Background The wheat dwarfing gene increases lodging resistance, the grain number per spike and harvest index. Dwarf Polish wheat (Triticum polonicum L., 2n = 4x = 28, AABB, DPW), initially collected from Tulufan, Xinjiang, China, carries a semi-dwarfing gene Rht-dp on chromosome 4BS. However, Rht-dp and its dwarfing mechanism are unknown. Results Homologous cloning and mapping revealed that Rht-dp is the ‘Green Revolution’ gene Rht-B1b. A haplotype analysis in 59 tetraploid wheat accessions showed that Rht-B1b was only present in T. polonicum. Transcriptomic analysis of two pairs of near-isogenic lines (NILs) of DPW × Tall Polish wheat (Triticum polonicum L., 2n = 4x = 28, AABB, TPW) revealed 41 differentially expressed genes (DEGs) as potential dwarfism-related genes. Among them, 28 functionally annotated DEGs were classed into five sub-groups: hormone-related signalling transduction genes, transcription factor genes, cell wall structure-related genes, reactive oxygen-related genes, and nitrogen regulation-related genes. Conclusions These results indicated that Rht-dp is Rht-B1b, which regulates pathways related to hormones, reactive oxygen species, and nitrogen assimilation to modify the cell wall structure, and then limits cell wall loosening and inhibits cell elongation, thereby causing dwarfism in DPW.

The semi-dwarfing gene Rht-dp from dwarf Polish wheat (Triticum polonicum L.) is the “Green Revolution” gene Rht-B1b

Background: The wheat dwarfing gene increases lodging resistance, the grain number per spike and harvest index. Dwarf Polish wheat (Triticum polonicum L., 2n = 4x = 28, AABB, DPW), initially collected from Tulufan, Xinjiang, China, carries a semi-dwarfing gene Rht-dp on chromosome 4BS. However, Rht-dp and its dwarfing mechanism are unknown.Results: Homologous cloning and mapping revealed that Rht-dp is the ‘Green Revolution’ gene Rht-B1b. A haplotype analysis in 59 tetraploid wheat accessions showed that Rht-B1b was only present in T. polonicum. Transcriptomic analysis of two pairs of near-isogenic lines (NILs) of DPW×Tall Polish wheat (Triticum polonicum L., 2n = 4x = 28, AABB, TPW) revealed 41 differentially expressed genes (DEGs) as potential dwarfism-related genes. Among them, 28 functionally annotated DEGs were classed into five sub-groups: hormone-related signalling transduction genes, transcription factor genes, cell wall structure-related genes, reactive oxygen-related genes, and nitrogen regulation-related genes. Conclusions: These results indicated that Rht-dp is Rht-B1b, which regulates pathways related to hormones, reactive oxygen species, and nitrogen assimilation to modify the cell wall structure, and then limits cell wall loosening and inhibits cell elongation, thereby causing dwarfism in DPW.