Figure 4. The proposed evolutionary trajectory of Ms2 and a model explaining the fertile and male-sterile phenotypes of different genotypes.

In the A and B diploid ancestor genomes, Ms2 othorlogs each accumulated one deleterious mutation. Three possible ORFs were predicted for the D diploid ancestor genome. ORF-I was not detected in hexaploidy wheat. In the ms2 mutant and in the transgenic Ms2-TRIM⁺wheat (Fielder background), Ms2 (ORF-III) is activated by the TRIM insertion, leading to male sterility. The EMS-mutagenized mutant lines, which have missense mutations in Ms2, produced normal or larger-than-mutant anthers. The purple arrow indicates Ms2, the gray arrows indicate truncated ORFs, the yellow arrow indicates the new ORF derived from the frame shift and the subsequent loss of the stop codon. The red triangles indicate the TRIM element in the promoter of Ms2.