Myb10-D confers PHS-3D resistance to pre-harvest sprouting by regulating NCED in ABA biosynthesis pathway of wheat.

Pre-harvest sprouting (PHS), the germination of grain before harvest, is a serious problem resulting in wheat yield and quality losses. Here, we mapped the PHS resistance gene PHS-3D from synthetic hexaploid wheat to a 2.4 Mb presence-absence variation (PAV) region and found that its resistance effect was attributed to the pleiotropic Myb10-D by integrated omics and functional analyses. Three haplotypes were detected in this PAV region among 262 worldwide wheat lines and 16 Aegilops tauschii, and the germination percentages of wheat lines containing Myb10-D was approximately 40% lower than that of the other lines. Transcriptome and metabolome profiling indicated that Myb10-D affected the transcription of genes in both the flavonoid and abscisic acid (ABA) biosynthesis pathways, which resulted in increases in flavonoids and ABA in transgenic wheat lines. Myb10-D activates 9-cis-epoxycarotenoid dioxygenase (NCED) by biding the secondary wall MYB-responsive element (SMRE) to promote ABA biosynthesis in early wheat seed development stages. We revealed that the newly discovered function of Myb10-D confers PHS resistance by enhancing ABA biosynthesis to delay germination in wheat. The PAV harboring Myb10-D associated with grain color and PHS will be useful for understanding and selecting white grained PHS resistant wheat cultivars.

The karyotype of Aegilops geniculata and its use to identify both addition and substitution lines of wheat.

BACKGROUND: The annual allotetraploid species Aegilops geniculata harbors a number of traits relevant for wheat improvement. An effective cytogenetic method has yet to be developed to distinguish between each of its 14 chromosomes. RESULTS: A fluorescence in situ hybridization (FISH) approach was adopted to describe the karyotype of Ae. geniculata. Each of its 14 chromosomes was unequivocally recognized using a cocktail of three probes, namely pTa-713, (AAC)5 and pTa71. FISH karyotyping was then used to detect and characterize selections from an Ae. geniculata × bread wheat wide cross of a chromosome 1Mg disomic addition line and three 4Mg(4B) substitution lines. The identity of the addition line was confirmed by the presence of Glu-M1, detected both using an SDS-PAGE separation of endosperm proteins and by applying a PCR assay directed at the Glu-M1 locus. The status of the substitution lines was validated by genotyping using a wheat single nucleotide polymorphism chip. CONCLUSION: FISH karyotyping based on pTa-713, (AAC)5 and pTa71 will be useful for determining the contribution of Ae. geniculata to derivatives of an Ae. geniculata × wheat wide cross. SNP chip-based genotyping is effective for confirming the status of whole chromosome wheat/alien substitution lines.

Introgression of Powdery Mildew Resistance Gene Pm56 on Rye Chromosome Arm 6RS Into Wheat.

Powdery mildew, caused by the fungus Blumeria graminis f. sp. tritici, represents a yield constraint in many parts of the world. Here, the introduction of a resistance gene carried by the cereal rye cv. Qinling chromosome 6R was transferred into wheat in the form of spontaneous balanced translocation induced in plants doubly monosomic for chromosomes 6R and 6A. The translocation, along with other structural variants, was detected using in situ hybridization and genetic markers. The differential disease response of plants harboring various fragments of 6R indicated that a powdery mildew resistance gene(s) was present on both arms of rye chromosome 6R. Based on karyotyping, the short arm gene, designated Pm56, was mapped to the subtelomere region of the arm. The Robertsonian translocation 6AL⋅6RS can be exploited by wheat breeders as a novel resistance resource.

Fluorescence in situ hybridization karyotyping reveals the presence of two distinct genomes in the taxon Aegilops tauschii.

BACKGROUND: Aegilops tauschii is the donor of the bread wheat D genome. Based on spike morphology, the taxon has conventionally been subdivided into ssp. tauschii and ssp. strangulata. The present study was intended to address the poor match between this whole plant morphology-based subdivision and genetic relationships inferred from genotyping by fluorescence in situ hybridization karyotyping a set of 31 Ae. tauschii accessions. RESULTS: The distribution of sites hybridizing to the two probes oligo-pTa-535 and (CTT)10 split the Ae. tauschii accessions into two clades, designated Dt and Ds, which corresponded perfectly with a previously assembled phylogeny based on marker genotype. The Dt cluster was populated exclusively by ssp. tauschii accessions, while the Ds cluster harbored both ssp. strangulata and morphologically intermediate accessions. As a result, it is proposed that Ae. tauschii ssp. tauschii is restricted to carriers of the Dt karyotype: their spikelets are regularly spaced along the rachis, at least in the central portion of their spike. Accessions classified as Ae. tauschii ssp. strangulata carry the Ds karyotype; their spikelets are irregularly spaced. Based on this criterion, forms formerly classified as ssp. tauschii var. meyeri have been re-designated ssp. strangulata var. meyeri. CONCLUSIONS: According to the reworking of the taxon, the bread wheat D genome was most probably donated by ssp. strangulata var. meyeri. Chromosomal differentiation reveals intra-species taxon of Ae. tauschii. Ae. tauschii ssp. tauschii has more distant relationship with breed wheat than ssp. strangulata and can be used for breeding improving effectively.