Wheat cleistogamy is expressed by the dosage effect of homoeologous AP2 mutant alleles carrying a point mutation in the miR172 target site

Abstract

Cleistogamy, or closed flowering, has received significant attention in wheat (Triticum aestivum) due to its wide range of applications. A stable cleistogamy system in barley (Hordeum vulgare), regulated by a single gene (cly1), has been successfully utilized in practical breeding. The aim of this study was to establish stable cleistogamy in hexaploid wheat by combining point mutations in the microRNA172 target site of three AP2 homoeologs, which are the wheat orthologs of barley Cly1. Triple mutants carrying the three relevant mutant AP2 alleles successfully exhibited cleistogamy resulting from suppression of lodicule swelling. Further investigation revealed that strong mutant alleles from two homoeologous loci (AP2-B and AP2-D) were necessary and sufficient to induce cleistogamy equivalent to that in barley, which stably suppressed lodicule development. The analysis also demonstrated that the total dosage of mutant AP2 alleles contributed to lodicule suppression and cleistogamy, likely correlating with the gene expression levels. Approaches for resolving the compact spike trait, which is expressed simultaneously with cleistogamy and is disadvantageous in practice, are also discussed.