Molecular mapping of the suppressor gene Igc1 to the gametocidal gene Gc3-C1 in common wheat

Gametocidal genes: from a discovery to the application in wheat breeding

Some species of the genus Aegilops, a wild relative of wheat, carry chromosomes that after introducing to wheat exhibit preferential transmission to progeny. Their selective retention is a result of the abortion of gametes lacking them due to induced chromosomal aberrations. These chromosomes are termed Gametocidal (Gc) and, based on their effects, they are categorized into three types: mild, intense or severe, and very strong. Gc elements within the same homoeologous chromosome groups of Aegilops (II, III, or IV) demonstrate similar Gc action. This review explores the intriguing dynamics of Gc chromosomes and encompasses comprehensive insights into their source species, behavioral aspects, mode of action, interactions, suppressions, and practical applications of the Gc system in wheat breeding. By delving into these areas, this work aims to contribute to the development of novel plant genetic resources for wheat breeding. The insights provided herein shed light on the utilization of Gc chromosomes to produce chromosomal rearrangements in wheat and its wild relatives, thereby facilitating the generation of chromosome deletions, translocations, and telosomic lines. The Gc approach has significantly advanced various aspects of wheat genetics, including the introgression of novel genes and alleles, molecular markers and gene mapping, and the exploration of homoeologous relationships within Triticeae species. The mystery lies in why gametes possessing Gc genes maintain their normality while those lacking Gc genes suffer abnormalities, highlighting an unresolved research gap necessitating deeper investigation.

Development of Wheat-Aegilops caudata Introgression Lines and Their Characterization Using Genome-Specific KASP Markers

Aegilops caudata L. [syn. Ae. markgrafii (Greuter) Hammer], is a diploid wild relative of wheat (2n = 2x = 14, CC) and a valuable source for new genetic diversity for wheat improvement. It has a variety of disease resistance factors along with tolerance for various abiotic stresses and can be used for wheat improvement through the generation of genome-wide introgressions resulting in different wheat-Ae. caudata recombinant lines. Here, we report the generation of nine such wheat-Ae. caudata recombinant lines which were characterized using wheat genome-specific KASP (Kompetitive Allele Specific PCR) markers and multi-color genomic in situ hybridization (mcGISH). Of these, six lines have stable homozygous introgressions from Ae. caudata and will be used for future trait analysis. Using cytological techniques and molecular marker analysis of the recombinant lines, 182 KASP markers were physically mapped onto the seven Ae. caudata chromosomes, of which 155 were polymorphic specifically with only one wheat subgenome. Comparative analysis of the physical positions of these markers in the Ae. caudata and wheat genomes confirmed that the former had chromosomal rearrangements with respect to wheat, as previously reported. These wheat-Ae. caudata recombinant lines and KASP markers are useful resources that can be used in breeding programs worldwide for wheat improvement. Additionally, the genome-specific KASP markers could prove to be a valuable tool for the rapid detection and marker-assisted selection of other Aegilops species in a wheat background.

Cytological observation of chromosome breakage in wheat male gametophytes caused by gametocidal action of Aegilops triuncialis-derived chromosome 3Ct

In this study, we investigated the chromosome breakage caused by gametocidal (Gc) chromosome 3C^t and its interaction with the suppressor gene Igc1 (inhibitor of gametocidal gene 1) on wheat chromosome 3B. We demonstrated cytologically that patterns of 3C^t-induced chromosomal fragmentation in microspores differed from patterns observed for other Gc genes. Uninuclear microspores of the monosomic 3C^t addition line had high frequencies of micronuclei, possibly explaining its low fertility. Chromosome fragmentation was observed in prometaphase and metaphase of the first pollen mitosis in the monosomic 3C^t addition line. Patterns of chromosome fragmentation were different from those previously reported for Gc chromosomes 2S of Aegilops speltoides, 4S^sh of Ae. sharonensis and 2C^cy of Ae. cylindrica; many chromosome fragments were observed in prometaphase of the first pollen mitosis in the monosomic 3C^t addition plants. In anthers at the binuclear stage, many microspores at the uninuclear stage coexisted with normally developed microspores.