An ABA-associated ZbNAC83 – ZbAG module contributes to female-to-male floral transition in Zanthoxylum bungeanum

Abstract

Plant sex reversal reflects developmental plasticity in floral sexual expression under genetic and environmental variation. Zanthoxylum bungeanum is a woody spice crop generally regarded as dioecious, but female-to-male floral transition has been increasingly observed in female trees across several major production regions in recent years, resulting in reduced fruit set and yield. Using developmental cytology, hormone profiling, transcriptomics, hormone treatments, and gene silencing assays, we found that ABA accumulation at the S2 stage was associated with female-to-male floral transition. Fluridone treatment before visible sex differentiation markedly reduced the proportion of male flowers, supporting a role for ABA biosynthesis during the early phase of floral sex specification. The floral homeotic gene ZbAGAMOUS (ZbAG) was identified as a candidate gene associated with reproductive organ identity and pistil retention during sex transition. Our data support a model in which elevated ABA is associated with increased ZbNAC83 expression and reduced ZbAG expression. ZbNAC83 binds an ABRE-containing fragment of the ZbAG promoter and represses reporter activity, consistent with a role in promoting male organ differentiation. These findings support a model in which an ABA-associated ZbNAC83–ZbAG module contributes to the loss of female floral identity during early floral sex transition in Z. bungeanum.