PaDSPD, a MYB-like Transcription Factor is linked with the Diurnally Synchronized Protogynous Dichogamy flowering type in avocado
Avocado (Persea americana) exhibits a distinctive flowering pattern in which each flower opens first as a female and later as a male in a process known as diurnally synchronous protogynous dichogamy (DSPD). Avocado varieties are classified into two types: Flowers of Type A cultivars open as female in the morning on day 1 and as male in the afternoon on day 2, while those of Type B cultivars open as female in the afternoon on day 1 and as male in the morning on day 2. The DSPD flowering system hinders self-pollination and promotes cross-pollination to maintain genetic diversity and is linked with higher yield in some cultivars. However, the genetic and molecular mechanism controlling DSPD is not fully known, limiting breeding efforts to improve avocado pollination compatibility and yield. In this study, using high-density markers, we conducted population structure analyses of a geographically diverse avocado collection, which revealed three genetically diverse and distinct subgroups corresponding to the major geographical origins of avocado: Mexican, Guatemalan, and West Indian. This panel, which includes both Type A and B cultivars, was used for genome-wide association studies (GWAS) employing multiple models (EMAXX, GLM, and MLM). These analyses identified a precise 20-Kb genomic region on chromosome 10 associated with flowering type A and B. Remarkably, all significant markers were delineated to a single gene encoding an R2R3 type MYB-like transcription factor, named here as Persea americana diurnally synchronous protogynous dichogamy (PaDSPD). These results were verified using bulked segregant analyses in a mapping population segregating for flowering types. Analysis of marker genotyping data revealed that Type A always occurs as heterozygous and Type B as homozygous. Mendelian segregation analysis revealed that flowering type in avocado is inherited in a modified 2:1 (Type A: Type B) ratio suggesting that one of the homozygous genotypes is likely lethal. Amino acid comparisons of the two heterozygous PaDSPD alleles revealed several non-synonymous amino acid substitutions, which, along with possible differential transcriptional regulation, potentially influence the contrasting flowering types. For marker-assisted selection, competitive allele-specific PCR markers were developed targeting the PaDSPD variants. These markers successfully distinguished Type A and Type B accessions with perfect accuracy. These findings contribute to the genetic dissection of avocado flowering type and offer molecular markers for breeding programs aimed at improving avocado pollination efficiency and productivity