The influence of mutated genes on sporogenesis

Summary

The course of meiosis in higher plants is controlled by a large number of genes, the function of which can be discerned by means of mutants showing any kind of meiotic anomaly. In general, there are three main groups of genes belonging to this system. The as-genes control the pairing behaviour of the homologous chromosomes, causing asynapsis in the mutated condition. The ds-genes are responsible for chiasma formation and chiasma frequency, causing desynapsis in the mutated condition. As- and ds-genes influence micro- and macrosporogenesis in a similar way but the ms-genes become effective only in microsporogenesis, resulting in a complete breakdown of meiosis at a stage specific for each gene of the group.

In Pisum sativum, 58 mutants showing genetically conditioned meiotic anomalies have been cytogenetically analysed: 34 of them belong to the ds- and 7 to the as-group; one gene causes asynaptic as well as desynaptic effects; 13 genotypes are male sterile due to degeneration of the chromosomes; the remaining 3 genes cause less specific meiotic disturbances. The lethality of a mutant can be overcome by distinct environmental conditions but the mutant is sterile because of manifold meiotic anomalies.

One gene in the Pisum genome controls the transition from the vegetative to the reproductive stage of the plants. Other genes influence the differentiation of the growing points in such a way that the sporogenic tissues are not formed. In these mutants, no sporocytes are present which can undergo meiosis.

From the findings available for many species of the plant kingdom, it can be assumed that hundreds of genes controlling meiosis are present in the genome of each higher plant.