Magnesium Increases Homoeologous Crossover Frequency During Meiosis in ZIP4 (Ph1 Gene) Mutant Wheat-Wild Relative Hybrids

Abstract

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 70 Mb 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 70 Mb 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)2·4H2O or Mg SO4·7H2O) was analyzed. 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 analyzed hybrids, when plants were irrigated with a 1 mM Mg2+ solution. These observations suggest a role for magnesium supplementation in improving the success of genetic material introgression from wild relatives into wheat.

Applying the latest advances in genomics and phenomics for trait discovery in polyploid wheat

“…Genotype‐independent transformation is of particular interest when considering applications for gene editing, which are not regulated as genetically modified organisms in North America, Japan and elsewhere, though they are in Europe. Gene‐editing systems such as TALENs and CRISPR‐Cas9 have now been demonstrated to function in wheat including the production of transgene‐free edited lines (Wang et al ., ; Zhang et al ., ; Rey et al ., ). Beyond the most common use of CRISPR‐Cas9, to induce small deletions that lead to frame‐shifts and knock‐outs, this may involve more complex editing such as targeted gene insertion or specific base editing (for review, see Adli, ).…”

Validation and characterisation of a wheat GENIE3 network using an independent RNA-Seq dataset

“…New germplasm resources in wheat, such as the in silico TILLING resource [41], can be rapidly leveraged for functional characterisation of candidate genes in planta . Transgenic approaches such as CRISPR [45] and virus-induced gene silencing (VIGS) [46] can now be used in wheat to validate gene function. The GENIE3 network can be accessed through the KnetMiner web application and using R scripts available from https://github.com/Uauy-Lab/GENIE3_scripts.…”

Genome-wide transcription during early wheat meiosis is independent of synapsis, ploidy level and thePh1locus

“…The locus was further defined to a smaller region (Griffith et al, 2006; Al-Kaff et al, 2008), now defined to 0.5Mb in size and containing 25 genes (7 HC + 18 LC genes), from which only two are expressed in our RNA-Seq data. One of these two genes is the duplicated ZIP4 gene ( TaZIP4-B2 ), which has been recently identified as the gene responsible for both promoting homologous CO and restricting homoeologous CO (Rey et al, 2017, 2018a). Another gene within the Ph1b deletion, termed by the authors as C-Ph1 , was also recently proposed to contribute to the Ph1 effect on recombination, specifically during metaphase I (Bhullar et al, 2014); however, this gene does not show any expression in our RNA-Seq data.…”

“…The Ph1 locus was recently defined to a region on chromosome 5B containing a duplicated 3B chromosome segment carrying the major meiotic gene ZIP4 and a heterochromatin tandem repeat block, inserted within a cluster of CDK2-like genes (Griffiths et al, 2006; Al-Kaff et.al., 2008; Martín et al, 2014, 2017). The duplicated ZIP4 gene ( TaZIP4-B2 ) within this cluster is responsible for both promotion of homologous CO and restriction of homoeologous CO, and is involved in improved synapsis efficiency (Rey et al, 2017, 2018a). The CDK2-like gene cluster has an effect on premeiotic events, its absence giving rise to delayed premeiotic replication and associated effects on chromatin and histone H1 phosphorylation (Greer et al, 2010).…”