Biology subjects

Smedley, M.

Publications and source records attributed to Smedley, M..

6 recordsLinked to original sources

bioRxiv2023

Septoria tritici blotch resistance gene Stb15 encodes a lectin receptor-like kinase

Septoria tritici blotch (STB), caused by the Dothideomycete fungus Zymoseptoria tritici, is of one of the most damaging diseases of bread wheat (Triticum aestivum)1 and the target of costly fungicide applications2. In line with the fungus apoplastic lifestyle, STB resistance genes isolated to date encode receptor-like kinases (RLKs) including a wall-associated kinase (Stb6) and a cysteine-rich kinase (Stb16q)3,4. Here, we used genome-wide association studies (GWAS) on a panel of 300 whole-genome shotgun-sequenced diverse wheat landraces (WatSeq consortium) to identify a 99 kb region containing six candidates for the Stb15 resistance gene. Mutagenesis and transgenesis confirmed a gene encoding an intronless G-type lectin RLK (LecRK) as Stb15. The characterisation of Stb15 exemplifies the unexpected diversity of RLKs conferring Z. tritici resistance in wheat.

genetics↗

bioRxiv2023

DMC1 stabilizes synapsis and crossover at high and low temperatures during wheat meiosis

Effective chromosome synapsis and crossover during meiosis are essential for fertility, especially in grain crops such as wheat. These processes function most efficiently in wheat at temperatures between 17-23 {degrees}C, although the genetic mechanisms for such temperature dependence are unknown. In a previously identified mutant of the hexaploid wheat reference variety Chinese Spring lacking the long arm of chromosome 5D, exposure to low temperatures during meiosis resulted in asynapsis and crossover failure. In a second mutant (ttmei1), containing a 4 Mb deletion in chromosome 5DL, exposure to 13 {degrees}C led to similarly high levels of asynapsis and univalence. Moreover, exposure to 30 {degrees}C led to a significant, but less extreme effect on crossover. Previously, we proposed that, of 41 genes deleted in this 4 Mb region, the major meiotic gene TaDMC1-D1 was the most likely candidate for preservation of synapsis and crossover at low (and possibly high) temperatures. In the current study, using RNA-guided Cas9, we developed a new Chinese Spring CRISPR mutant, containing a 39 bp deletion in the 5D copy of DMC1, representing the first reported CRISPR-Cas9 targeted mutagenesis in Chinese Spring, and the first CRISPR mutant for DMC1 in wheat. In controlled environment experiments, wild-type Chinese Spring, CRISPR dmc1-D1 and backcrossed ttmei1 mutants were exposed to either high or low temperatures during the temperature-sensitive period from premeiotic interphase to early meiosis I. After 6-7 days at 13 {degrees}C, crossover decreased by over 95% in the dmc1-D1 mutants, when compared with wild-type plants grown under the same conditions. After 24 hours at 30 {degrees}C, dmc1-D1 mutants exhibited a reduced number of crossovers and increased univalence, although these differences were less marked than at 13 {degrees}C. Similar results were obtained for ttmei1 mutants, although their scores were more variable, possibly reflecting higher levels of background mutation. These experiments confirm our previous hypothesis that DMC1-D1 is responsible for preservation of normal synapsis and crossover at low and, to a certain extent, high temperatures. Given that reductions in crossover have significant effects on grain yield, these results have important implications for wheat breeding, particularly in the face of climate change. Key messageThe meiotic recombination gene DMC1 on wheat chromosome 5D preserves normal chromosome synapsis and crossover during periods of high and low temperature.

molecular biology↗

bioRxiv2023

Modification of amyloplast size in wheat endosperm through mutation of PARC6 affects starch granule morphology

Starch granule morphology is a major factor determining the functional and nutritional properties of starch. Here, we reveal amyloplast structure plays an important role in starch granule morphogenesis in wheat endosperm. Wheat amyloplasts contain large discoid A-type granules and small spherical B-type granules. We isolated a mutant in durum wheat defective in the plastid division protein PARC6, which had increased plastid size in both leaves and endosperm. Endosperm amyloplasts of the mutant contained more A- and B-type granules than those of the wild type. In mature grains, the mutant had larger A- and B-type granules than the wild type, and its A-type granules had a highly aberrant, lobed surface. This defect in granule morphology was already evident at early stages of grain development, when granule size was identical between the mutant and the wild type, and occurred without obvious alterations in starch polymer structure and composition. Plant growth and photosynthetic efficiency, as well as the size, number and starch content of grains, were not affected in the Ttparc6 mutants despite the large changes in plastid size. Interestingly, mutation of the PARC6 paralog, ARC6, in durum wheat did not increase plastid or starch granule size. We suggest this is because TtPARC6 can complement disrupted TtARC6 function by interacting with PDV2, the outer plastid envelope protein that typically interacts with ARC6 to promote plastid division. We propose that amyloplast compartment size and available stromal volume play important roles in determining starch granule size, shape and number per amyloplast.

plant biology↗

bioRxiv2023

ZIP4 is required for normal progression of synapsis and for over 95% of crossovers in wheat meiosis.

Tetraploid and hexaploid wheat have multiple genomes, with successful meiosis and preservation of fertility relying on synapsis and crossover only taking place between homologous chromosomes. In hexaploid wheat, the major meiotic gene TaZIP4-B2 (Ph1) on chromosome 5B, promotes crossover between homologous chromosomes, whilst suppressing crossover between homeologous (related) chromosomes. Tetraploid wheat has three ZIP4 copies: TtZIP4-A1 on chromosome 3A, TtZIP4-B1 on 3B and TtZIP4-B2 on 5B. Previous studies showed that ZIP4 mutations eliminate approximately 85% of crossovers, consistent with loss of the class I crossover pathway. Here, we show that disruption of two ZIP4 gene copies in Ttzip4-A1B1 double mutants, results in a 76-78% reduction in crossovers when compared to wild-type plants. Moreover, when all three copies are disrupted in Ttzip4-A1B1B2 triple mutants, crossover is reduced by over 95%, suggesting that the TtZIP4-B2 copy is also affecting class II crossovers. This implies that, in wheat, the class I and class II crossover pathways may be interlinked. When ZIP4 duplicated and diverged from chromosome 3B on wheat polyploidization, the new 5B copy, TaZIP4-B2, may have acquired an additional function to stabilize both crossover pathways. In plants deficient in all three ZIP4 copies, synapsis is delayed and does not complete, consistent with our previous studies in hexaploid wheat, when a similar delay in synapsis was observed in a 59.3Mb deletion mutant, ph1b, encompassing the TaZIP4-B2 gene on chromosome 5B. These findings confirm the requirement of ZIP4-B2 for efficient synapsis, and suggest that TtZIP4 genes have a stronger effect on synapsis than previously described in Arabidopsis and rice. Thus, ZIP4-B2 accounts for the two major phenotypes reported for Ph1, promotion of homologous synapsis and suppression of homeologous crossover. Key messageIn tetraploid wheat, ZIP4 is required for efficient chromosome synapsis and for over 95% of crossovers, involving both the class I and class II crossover pathways. Author contribution statementTD grew and maintained the plants, made the crosses, carried out the KASP genotyping and sequencing, carried out the meiotic metaphase I studies and produced the corresponding figure, and wrote the manuscript. M-DR scored chromosome crossover, performed the statistical analysis and produced the graphs. AM selected the TILLING mutant, carried out the immunolocalization and FISH experiments and produced the immunolocalization figure; SH and MS developed the Ttzip4-B2 CRISPR mutant in Kronos using RNA-guided Cas9 and produced the CRISPR Ttzip4-B2 sequence figure; AKA designed the KASP primers; AM and GM provided the concept, provided thoughts and guidance, and revised and edited the manuscript. Conflict of interestThe authors declare that they have no conflict of interest.

cell biology↗

bioRxiv2020

Increased and ectopic expression of Triticum polonicum VRT-A2 underlies elongated glumes and grains in hexaploid wheat in a dosage-dependent manner

Flower development is a major determinant of yield in crops. In wheat, natural variation for the size of spikelet and floral organs is particularly evident in Triticum polonicum, a tetraploid subspecies of wheat with long glumes, lemmas, and grains. Using map-based cloning, we identified VRT2, a MADS-box transcription factor belonging to the SVP family, as the gene underlying the T. polonicum long-glume (P1) locus. The causal P1 mutation is a sequence re-arrangement in intron-1 that results in both increased and 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 species 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 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 impact on agronomic traits in a dosage-dependent manner in polyploid crops. One-sentence summaryAn intron-1 rearrangement in the MADS-box transcription factor VRT-A2 leads to its misexpression and defines the long-glume phenotype of Polish wheat (T. polonicum).

plant biology↗

bioRxiv2018

Magnesium increases homoeologous crossover frequency in ZIP4 (Ph1) mutant wheat-wild relative hybrids

Wild relatives provide an important source of useful traits in wheat breeding. Wheat and wild relative hybrids have been widely used in breeding programs to introduce such traits into wheat. However, successful introgression is limited by the low frequency of homoeologous crossover (CO) between wheat and wild relative chromosomes. Hybrids between wheat carrying a 70Mb deletion on chromosome 5B (ph1b) and wild relatives, have been exploited to increase the level of homoeologous CO, allowing chromosome exchange between their chromosomes. In ph1b-rye hybrids, CO number increases from a mean of 1 CO to 7 COs per cell. CO number can be further increased up to a mean of 12 COs per cell in these ph1b hybrids by treating the plants with Hoagland solution. More recently, it was shown that the major meiotic crossover gene ZIP4 on chromosome 5B (TaZIP4-B2) within the 70Mb deletion, was responsible for the restriction of homoeologous COs in wheat-wild relative hybrids, confirming the ph1b phenotype as a complete Tazip4-B2 deletion mutant (Tazip4-B2 ph1b). In this study, we have identified the particular Hoagland solution constituent responsible for the increased chiasma frequency in Tazip4-B2 ph1b mutant-rye hybrids and extended the analysis to Tazip4-B2 TILLING and CRISPR mutant-Ae variabilis hybrids. Chiasma frequency at meiotic metaphase I, in the absence of each Hoagland solution macronutrient (NH4 H2PO4, KNO3, Ca (NO3)2{middle dot}4H2O or Mg SO4{middle dot}7H2O) was analysed. A significant decrease in homoeologous CO frequency was observed when the Mg2+ ion was absent. A significant increase of homoeologous CO frequency was observed in all analysed hybrids, when plants were irrigated with a 1mM Mg2+ solution. These observations suggest a role for magnesium supplementation in improving the success of genetic material introgression from wild relatives into wheat.

cell biology↗