Biology subjects

Draeger, T. N.

Publications and source records attributed to Draeger, T. N..

3 recordsLinked to original sources

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

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↗

bioRxiv2019

Dmc1 is a candidate for temperature tolerance during wheat meiosis

We have assessed the effects of high and low temperatures on meiotic chromosome synapsis and crossover formation in the hexaploid wheat (Triticum aestivum L.) variety Chinese Spring. At low temperatures, asynapsis and chromosome univalence have been observed before in Chinese Spring lines lacking the long arm of chromosome 5D (5DL), which led to the proposal that 5DL carries a gene (Ltp1) that stabilises wheat chromosome pairing at low temperatures. In the current study, Chinese Spring wild type and 5DL interstitial deletion mutant plants were exposed to low (13{degrees}C) or high (30{degrees}C) temperatures in controlled environment rooms during a period from premeiotic interphase to early meiosis I. A 5DL deletion mutant was identified whose meiotic chromosomes exhibit extremely high levels of asynapsis and chromosome univalence at metaphase I after seven days at 13{degrees}C. This suggests that the mutant, which we name ttmei1 (temperature tolerance in meiosis 1) has a deletion of a gene that, like Ltp1, normally stabilises chromosome pairing at low temperatures. Immunolocalisation of the meiotic proteins ASY1 and ZYP1 on ttmei1 mutants showed that low temperature results in a failure to complete synapsis at pachytene. After 24 hours at 30{degrees}C, ttmei1 mutants exhibited a reduced number of crossovers and increased univalence, but to a lesser extent than at 13{degrees}C. KASP genotyping revealed that ttmei1 has a 4 Mb deletion in 5DL. Of 41 genes within this deletion region, the strongest candidate for the stabilisation of chromosome pairing at low (and possibly high) temperatures is the meiotic recombination gene Dmc1.\n\nKey messageThe meiotic recombination gene Dmc1 on wheat chromosome 5D has been identified as a candidate for the maintenance of normal chromosome synapsis and crossover at low and possibly high temperatures.

plant biology↗