Magnesium increases homoeologous crossover frequency inZIP4(Ph1) mutant wheat-wild relative hybrids

Abstract

28Wild relatives provide an important source of useful traits in wheat breeding. Wheat and wild relative hybrids 29 have been widely used in breeding programs to introduce such traits into wheat. However, successful introgression 30 is limited by the low frequency of homoeologous crossover (CO) between wheat and wild relative chromosomes. 31Hybrids between wheat carrying a 70Mb deletion on chromosome 5B (ph1b) and wild relatives, have been 32 exploited to increase the level of homoeologous CO, allowing chromosome exchange between their 33 chromosomes. In ph1b-rye hybrids, CO number increases from a mean of 1 CO to 7 COs per cell. CO number 34 can be further increased up to a mean of 12 COs per cell in these ph1b hybrids by treating the plants with Hoagland 35 solution. More recently, it was shown that the major meiotic crossover gene ZIP4 on chromosome 5B (TaZIP4-36 B2) within the 70Mb deletion, was responsible for the restriction of homoeologous COs in wheat-wild relative 37 hybrids, confirming the ph1b phenotype as a complete Tazip4-B2 deletion mutant (Tazip4-B2 ph1b). In this study, 38we have identified the particular Hoagland solution constituent responsible for the increased chiasma frequency 39 in Tazip4-B2 ph1b mutant-rye hybrids and extended the analysis to Tazip4-B2 TILLING and CRISPR mutant-Ae 40 variabilis hybrids. Chiasma frequency at meiotic metaphase I, in the absence of each Hoagland solution 41 macronutrient (NH4 H2PO4, KNO3, Ca (NO3)2·4H2O or Mg SO4·7H2O) was analysed. A significant decrease in 42 homoeologous CO frequency was observed when the Mg 2+ ion was absent. A significant increase of 43 homoeologous CO frequency was observed in all analysed hybrids, when plants were irrigated with a 1mM Mg 2+ 44 solution. These observations suggest a role for magnesium supplementation in improving the success of genetic 45 material introgression from wild relatives into wheat. 46 47 48 49 50 51 52 53 54 55 Despite possessing related ancestral genomes (genome AABBDD), bread wheat behaves as a diploid during 56 meiosis. Deletion of chromosome 5B in tetraploid and hexaploid wheat results in a level of incorrect chromosome 57 pairing and exchange, visualised as a low level of multivalents at metaphase I, and homoeologous crossovers 58 (COs) between related chromosomes in wheat-wild relative hybrids (Riley and Chapman, 1958; Sears and 59 Okamoto, 1958). From these observations, it was proposed that chromosome 5B carries a locus termed Pairing 60 homoeologous 1 (Ph1), which evolved on wheat's polyploidisation and restricted chromosome pairing and COs 61 to true homologues (Riley and Chapman, 1958). A hexaploid wheat cv. Chinese Spring (CS) line carrying a 70Mb 62 deletion on the long arm of chromosome 5B (ph1b) has been exploited over the last 40 years to allow exchange 63 between wild relative and wheat chromosomes. Recently, it was shown that on wheat's polyploidisation, a 64 segment of 3B carrying the major crossover gene ZIP4 and a block of heterochromatin, duplicated and inserted 65 between two CDK2-like g...

An Induced Mutation in HvRECQL4 Increases the Overall Recombination and Restores Fertility in a Barley HvMLH3 Mutant Background

“…The availability of a demonstrated effective non-GM anti-CO allele of RECQL4 in barley opens the possibility of testing whether increasing recombination will, or will not, have an enabling role in general or specific aspects of crop improvement such as introgression breeding. Given the limits to the plasticity of recombination remain unknown, intriguing options remain to be explored, such as combining recql4 G 700 D in barley with other mutations or combining genetic variants with “treatments” such as temperature (Phillips et al, 2015 ; Modliszewski et al, 2018 ), chemicals (Rey et al, 2018 ), or speed breeding conditions (Ghosh et al, 2018 ). While we have underlined the potentially important role of RECQL4 as an anti-CO factor in barley, a major challenge remains in assessing if and how recql4 G 700 D can be used effectively to improve the rate of genetic gain in barley crop improvement.…”

ZIP4is required for normal progression of synapsis and for over 95% of crossovers in wheat meiosis

“…CRISPR Ttzip4-B2 mutants were generated in Kronos by the BRACT group at the John Innes Centre. Three single guide RNAs (sgRNA) specific to the hexaploid wheat TaZIP4-B2 gene (Gene ID: TraesCS5B02G255100.1), and previously reported in Rey et al, 2018 were used.…”

Data_Sheet_4.zip

“…The availability of a demonstrated effective non-GM anti-CO allele of RECQL4 in barley opens the possibility of testing whether increasing recombination will, or will not, have an enabling role in general or specific aspects of crop improvement such as introgression breeding. Given the limits to the plasticity of recombination remain unknown, intriguing options remain to be explored, such as combining recql4 G700D in barley with other mutations or combining genetic variants with "treatments" such as temperature (Phillips et al, 2015;Modliszewski et al, 2018), chemicals (Rey et al, 2018), or speed breeding conditions (Ghosh et al, 2018). While we have underlined the potentially important role of RECQL4 as an anti-CO factor in barley, a major challenge remains in assessing if and how recql4 G700D can be used effectively to improve the rate of genetic gain in barley crop improvement.…”