An EjSPT-EjTCP4-EjRR8 Regulatory Module Links Cytokinin Homeostasis and Cell Proliferation to Fruit Growth in Loquat.

An EjSPT–EjTCP4–EjRR8 regulatory module is linked to cytokinin accumulation, cell proliferation, and fruit-size variation in loquat, with EjRR8 as a key regulator.

• Why it matters: Fruit size strongly affects yield and value, but the transcriptional circuitry connecting cytokinin homeostasis to cell proliferation during loquat fruit development remains unclear.
• What they did: The study compared two loquat cultivars with contrasting fruit sizes using hormone quantification, cytology, and transcriptome profiling, then performed gain- and loss-of-function tests for EjRR8 and upstream factor binding assays.
• The result: EjRR8 modulates cytokinin accumulation and cell proliferation, while EjSPT and EjTCP4 directly bind and synergistically activate EjRR8, providing a molecular framework for breeding larger-fruited loquat cultivars.