Synergistic effects of GmLFYa and GmLFYb on Compound Leaf Development in Soybean

Legume leaves exhibit diverse compound forms, with various regulatory mechanisms underlying the development. The transcription factor-encoding KNOXI genes are required to promote leaflet initiation in most compound-leafed angiosperms. In non-IRLC (inverted repeat-lacking clade) legumes, KNOXI are expressed in compound leaf primordia but not in others (IRLC). Recent studies have highlighted LFY genes' role in regulating leaflet initiation across legumes. The LFY functions in leaf development are well understood in IRLC legumes but remain unclear in non-IRLC legumes. Soybean, a major crop belonging to non-IRLC legumes, has limited research on the trifoliate leaf morphogenesis. Here, we comprehensively analyzed soybean trifoliate leaf development and characterized two GmLFY gene copies, GmLFYa and GmLFYb, in compound leaf morphogenesis. Analyzing the loss-of-function mutants revealed that Gmlfya displayed a low frequency of simple-like leaves, while the Gmlfyb showed no visible phenotype. However, the Gmlfya Gmlfyb double mutant predominantly displayed simple-like leaves. Additionally, mutations in two genes also affect floral development: each single mutant exhibited slightly deformed floral organs, while double mutant produced inflorescence-like structures. The transformation from floral meristems to inflorescence-like structures is similar to lfy mutant in Arabidopsis but quite different from M. truncatula and L. japonicus. These findings suggest that the two GmLFY genes in soybean collaboratively regulate both compound leaf and flower morphogenesis. Our study not only creates foundational mutant materials for future research on leaf and flower development in soybean but also reinforces the role of LFY orthologs as master regulators in compound leaf morphogenesis across a broader range of legume taxa than previously recognized.