A putative MYB35 ortholog is a candidate for the sex-determining genes in Asparagus officinalis

Asparagus officinalis (garden asparagus) is a dioecious perennial crop. For agricultural production of A. officinalis, male plants have advantages over female plants. The dioecism of A. officinalis is determined by the single dominant masculinizing M locus, which is involved in tapetal cell development in stamens, but thus far no specific M locus genes have been identified. We re-analyzed previously published RNA-Seq data for the A. officinalis transcriptome, cloned some genes, and discovered that a putative ortholog of MYB35, which is indispensable for tapetal cell development in Arabidopsis thaliana, is absent in the genome of female plants in A. officinalis. In a reverse transcription-PCR analysis, this gene (AoMYB35) exhibited strong expression in stamens in male flowers at an early developmental stage. In an in situ hybridization analysis, AoMYB35 mRNA was detected in tapetal cells in young male flowers. GFP-fused AoMYB35 was detected in the nucleus when expressed in onion epidermal cells. These results suggest that AoMYB35 is a male-specific gene encoding a putative transcription factor that acts in tapetal cells at an early stage of flower development in A. officinalis. Together, the results support the idea that AoMYB35 is a candidate for one of the M locus genes in A. officinalis.