Abstract
Plant LATERAL ORGAN BOUNDARIES DOMAIN (LBD) family is crucial for defining organ boundaries and participates in various developmental processes, but its role in fruit weight has rarely been elucidated. Here, we characterized an LBD gene, Physalis organ size 3 (POS3), in Physalis floridana, designated as PfPOS3. This gene exhibited high expression levels in floral meristems, carpels, and developing seeds and fruits when compared to Solanum pimpinellifolium and Solanum lycopersicum. The floral organ size, seed weight, and mature fruit weight were significantly reduced in PfPOS3 knockdown and knockout plants. Consistent with overexpression analyses, PfPOS3 promoted cell size and inhibited cell division during berry development. Moreover, overexpression of PfPOS3 and SlPOS3 shared identical phenotypic variation in transgenic Physalis plants. Both PfPOS3 and SlPOS3 interacted with Teosinte branched1/Cycloidea/Proliferating cell factor 15 (TCP15) and TCP18, and the POS3-TCP modules directly regulated the expression of Cyclin D1;1 (CYCD1;1) and CYCB1;1. Overall, POS3 may have the capability to orchestrate cell number and cell size, thus regulating fruit weight variation within Solanaceae. However, a significant reduction in the expression of SlPOS3 may result in a pronounced weakening or complete loss of this function within Solanum. Our findings shed new light on the reproductive organ size control, the developmental evolution of fruit morphology, and the breeding of Physalis crops.