At the breaking point: developmental and molecular insights into Physalis grisea fruit abscission

Fruit abscission is an agronomically important trait that would benefit from a deeper molecular understanding. Despite a prominent, deleterious, fruit drop phenotype, fruit abscission has yet to be characterized in Physalis grisea (groundcherry). Here we established a stage-resolved timeline of P. grisea pedicel abscission zone (AZ) development to expand the general knowledge of fruit abscission. We integrated microscopic imaging of the AZ, hormone (auxin and ethylene) applications, detachment force measurements, and gene expression analysis of AZ cells across maturation to connect the role of putative regulators to cell development and separation. A strong correlation between AZ development, hormone sensitivity, and force detachment was observed. RNA-seq showed upregulation of pathways involved in cell division/expansion early in AZ development, hormone signaling and transcriptional reprogramming at the middle stage, and cell wall degradation and protective barrier genes late in the abscission process. Furthermore, MADS-box transcription factors such as the P. grisea orthologs of JOINTLESS and MACROCALYX are co-expressed during AZ differentiation, suggesting involvement in the formation of AZ cells. These results provide a molecular and cellular framework for P. grisea fruit abscission, suggesting that key regulatory features of fruit abscission are shared within the Solanaceae. Characterization of fruit abscission in P. grisea is essential for understanding this trait to guide improvements needed for its adoption as a specialty crop in the United States.