Many species, including most flowering plants, are polyploid, possessing multiple genomes. During polyploidisation, fertility is preserved via the evolution of mechanisms to control the behaviour of these multiple genomes during meiosis. On the polyploidisation of wheat, the major meiotic gene ZIP4 duplicated and diverged, with the resulting new gene TaZIP4-B2 being inserted into chromosome 5B. Previous studies showed that this TaZIP4-B2 promotes pairing and synapsis between wheat homologous chromosomes, whilst suppressing crossover between related (homoeologous) chromosomes. Moreover, in wheat, the presence of TaZIP4-B2 preserves up to 50% of grain number. The present study exploits a ‘separation-of-function’ wheat Tazip4-B2 mutant named zip4-ph1d, in which the Tazip4-B2 copy still promotes correct pairing and synapsis between homologues (resulting in the same pollen profile and fertility normally found in wild type wheat), but which also allows crossover between the related chromosomes in wheat haploids of this mutant. This suggests an improved utility for the new zip4-ph1d mutant line during wheat breeding exploitation, compared to the previously described CRISPR Tazip4-B2 and ph1 mutant lines. The results also reveal that loss of suppression of homoeologous crossover between wheat chromosomes does not in itself reduce wheat fertility when promotion of homologous pairing and synapsis by TaZIP4-B2 is preserved.

/pdf/a-separation-of-function-zip4-wheat-mutant-allows-crossover-4oyjqzyluj.pdf

Chromosome techniques: Theory and practice

A separation-of-function ZIP4 wheat mutant allows crossover between related chromosomes and is meiotically stable

Higher plants are recognized as excellent genetic models to detect environmental mutagens, and are therefore, frequently used in monitoring studies. The genotoxic potential of carbendazim (fungicide) was investigated by using chromosome aberration in Allium cepa L. root tip cells. In this study, the effects of Carbendazim, a systemic fungicide were investigated in the mitotic cell division in onion (Allium cepa L.) root tip cells during germination. Allium cepa L. roots were treated with 1g/L, 2g/L and 3g/L concentrations of Carbendazim and distilled water as control at 6 hours, 12 hours and 18 hours duration. All the concentrations used, caused several abnormalities in mitotic cell divisions and the Mitotic Index in the onion root tip cells decreased when the concentrations of Carbendazim solution is increased.The total percentage of aberrations generally increased in a dose and time dependent manner. Life Sciences

Genotoxic effects of carbendazim (fungicide) on the root apical meristems of allium cepa l.

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 4H2O or Mg SO4 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.

/pdf/magnesium-increases-homoeologous-crossover-frequency-in-zip4-4xeuovn3zf.pdf

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

https://abt.ucpress.edu/content/ucpabt/37/8/501.full.pdf

Giemsa Staining of Chromosomes in Root Tip Cells

The seeds of 2 varieties of common Sunflower (Helianthus annuus L.) viz:USH-430 and KL-675 were treated to estimate the mutagenicity of both gamma-rays, sodium azide alone and in combination with a view to generate morphological macro-mutations and screen and ascertain the chromosomal aberrations followed by reduction of pollen fertility with increased doses. An attempt was made to know the genetic basis of the chromosomal aberrations. Such aberrations are a source of changes in the pattern of gene regulation at the time of differentiation leading to the formation of cultivars.

/pdf/chromosomal-induced-aberrations-in-sunflower-helianthus-26bnn4ifam.pdf

Chromosome techniques: Theory and practice

Citations

A separation-of-function ZIP4 wheat mutant allows crossover between related chromosomes and is meiotically stable

Genotoxic effects of carbendazim (fungicide) on the root apical meristems of allium cepa l.

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

Giemsa Staining of Chromosomes in Root Tip Cells

Chromosomal Induced Aberrations in Sunflower (Helianthus annuus. L) with Gamma-irradiation, Sodium Azide and Combined Treatments

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