Mutations within the miR172 target site of wheat AP2 homoeologs regulate lodicule size and rachis internode length

Closed fertilization in flowers, or cleistogamy, reduces the risk of fungal infection in Triticeae crops. In barley (Hordeum vulgare), cleistogamy is determined by a single recessive gene, cly1, which results from a single nucleotide polymorphism within the microRNA172 target site of the Apetala2 (AP2) transcription factor gene. The recessive cly1 allele negatively regulates the development of lodicules, keeping florets closed at anthesis. However, cleistogamy is not evident in hexaploid wheat (Triticum aestivum) cultivars. This study aimed at identifying mutations in wheat AP2 orthologs by ethyl methane sulfonate-induced mutagenesis and high-resolution melt analysis. Although flowers of AP2 mutants induced in the A and D genomes opened at anthesis, their lodicule size was significantly smaller, especially in the direction of depth, than that of wild-type plants. One of the mutants that carried a nucleotide replacement in AP2 from the D genome produced a compact spike caused by a substantial decrease in rachis internode length, analogous to the barley dense spike. Cleistogamous hexaploid wheat might be generated by combining effective mutant alleles of AP2-homoeologous genes.