The FataAP2-FataAP1-FataTOE Regulatory Cascade Regulates Floral Organ Development in Fagopyrum tataricum

Arabidopsis class A genes APETALA 1 (AP1) and AP2 determine sepal and petal identity; AP2 also acts as a repressor that directly negatively regulates AP1 expression to control flowering time, while TOE1 represses flowering by inhibiting CONSTANS (CO) activity. Petunia AP2-type ROB is required for perianth and pistil development, as well as the repression of B-function and TOE-type BEN. However, how AP1 and AP2 orthologs from Fagopyrum tataricum work together to regulateflowering and floral organ development remains unclear. F. tataricum is an edible and medical crop rich in bioactive phytochemicals that have health benefits. This plant has only one perianth whorl, making it an excellent model for exploring the development and evolution of apetaly. In this study, we found that AP1-like FataAP1, AP2-type FataAP2, and TOE-type FataTOE were expressed in the roots, stems, leaves, flowers, and fruits of tartary buckwheat and in all stages detected during floral bud differentiation and development. The Y1H assay and DLR suggested that FataAP2 directly activates FataAP1 transcription and that FataAP1 directly activates the transcription of FataTOE. The VIGS silencing of FataAP2, FataAP1, and FataTOE resulted in flowers with increased tepal numbers and partly abnormal outer-whorl stamens with reduced filament lengths and shriveled anthers without pollen grains. A hierarchical regulatory cascade, FataAP2-FataAP1-FataTOE, was uncovered, which modulated tepal numbers and outer-whorl stamen development during tartary buckwheat flower development. Our current research provides new insights into the molecular mechanism of floral organ development in tartary buckwheat and may provide new evidence for exploring the floral phenotypic differences between tartary buckwheat and common buckwheat.