A Duplicated Copy of the Meiotic Gene <i>ZIP4</i> Preserves up to 50% Pollen Viability and Grain Number in Polyploid Wheat
2021
Abdul Kader Alabdullah | Graham Moore | Azahara C. Martín
Although most flowering plants are polyploid, little is known of how the meiotic process evolves after polyploidisation to stabilise and preserve fertility. On wheat polyploidisation, the major meiotic gene <i>ZIP4</i> on chromosome 3B duplicated onto 5B and diverged (<i>TaZIP4-B2</i>). <i>TaZIP4-B2</i> was recently shown to promote homologous pairing, synapsis and crossover, and suppress homoeologous crossover. We therefore suspected that these meiotic stabilising effects could be important for preserving wheat fertility. A CRISPR <i>Tazip4-B2</i> mutant was exploited to assess the contribution of the 5B duplicated <i>ZIP4</i> copy in maintaining pollen viability and grain setting. Analysis demonstrated abnormalities in 56% of meiocytes in the <i>Tazip4-B2</i> mutant, with micronuclei in 50% of tetrads, reduced size in 48% of pollen grains and a near 50% reduction in grain number. Further studies showed that most of the reduced grain number occurred when <i>Tazip4-B2</i> mutant plants were pollinated with the less viable <i>Tazip4-B2</i> mutant pollen rather than with wild type pollen, suggesting that the stabilising effect of <i>TaZIP4-B2</i> on meiosis has a greater consequence in subsequent male, rather than female gametogenesis. These studies reveal the extraordinary value of the wheat chromosome 5B <i>TaZIP4-B2</i> duplication to agriculture and human nutrition. Future studies should further investigate the role of <i>TaZIP4-B2</i> on female fertility and assess whether different <i>TaZIP4-B2</i> alleles exhibit variable effects on meiotic stabilisation and/or resistance to temperature change.
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