SlSPL10, a Transcription Factor That Suppresses Lateral Bud Outgrowth in Tomato

Lateral bud outgrowth critically determines tomato plant architecture, canopy structure, photosynthate distribution, and fruit yield. SQUAMOSA promoter binding protein-like (SPL) transcription factors regulate multiple developmental processes; however, the role of SlSPL10 in controlling lateral bud outgrowth remains unknown. In this study, we used tomato cultivar Micro-Tom (wild-type, WT), SlSPL10 knockout mutants (slspl10#1 and slspl10#2), and overexpression lines (OE-SlSPL10#6 and OE-SlSPL10#7) to assess agronomic traits and phytohormone levels. The slspl10 mutants exhibited dwarfism, increased lateral bud number, and elongated buds, whereas OE-SlSPL10 lines suppressed bud outgrowth. Phytohormone and sucrose analyses revealed that slspl10 mutants displayed elevated levels of ZT, GA3, and sucrose, but reduced levels of IAA, ABA, and SA, whereas OE-SlSPL10 lines showed opposite trends. To dissect the underlying molecular mechanism, we demonstrated that SlSPL10 directly binds to GTAC motifs in the promoters of SlARF10a and SlABI3 using yeast one-hybrid (Y1H) assays, dual-luciferase reporter (DLR) assays, and chromatin immunoprecipitation-PCR (ChIP-PCR), thereby transactivating both target genes. Virus-induced gene silencing (VIGS) of SlARF10a or SlABI3 phenocopied the slspl10 mutants, showing increased lateral bud number and elongation. Hormone measurements in VIGS lines further indicated that silencing SlARF10a specifically reduced IAA content, whereas silencing SlABI3 specifically reduced ABA content; both lines also exhibited increased ZT, GA3, and sucrose, and decreased SA. Collectively, these results demonstrate that SlSPL10 directly targets SlARF10a and SlABI3 to modulate phytohormone and sucrose homeostasis, thereby precisely inhibiting lateral bud outgrowth in tomato.