The transcription factor LF1 controls compound leaf development by interacting with GmTCP3 and the <i>GmLFY</i> signaling network

Leaf morphology varies substantially across plant species. In soybeans, the regulation of compound leaf development remains poorly characterized, despite its critical role in plant architecture. Some soybean cultivars have compound leaves with up to five leaflets, while most are trifoliolate. Using genetic mapping, we identified a gene behind the leaflet number variation as LF1, an AP2/ERF transcription factor. High expression levels of LF1 were further observed in leaf primordium initiation sites, leaf primordia, and leaflet initiation domains. Transgenic overexpression of LF1 increased leaflet number. Further investigation revealed that LF1 regulates leaflet development through negative autoregulation via GCC-box cis-element binding. In addition to the role of LF1, the CRISPR-edited mutant of TEOSINTE-BRANCHED1/CYCLOIDEA/PCF3 (GmTCP3) displayed serrated blade margins in juvenile leaves and increased compound leaflet numbers. Protein interaction assays confirmed LF1 binding affinity for GmTCP3. Furthermore, we demonstrate that LF1 induces the expression of GmLFY, a key regulator of leaflet development. Altogether, our findings establish LF1 as a central regulator of soybean leaflet morphogenesis and reveal its mechanistic interactions with GmTCP3 and LEAFY (GmLFY), offering novel mechanistic insights into the genetic control of compound leaf development.