PubMed · 2026-05-22
Scientists used CRISPR to knock out all four cytokinin receptor proteins in rice, revealing that this single hormone governs everything from the plant's very first shoot to how many grain-bearing branches it produces — and that rice depends on cytokinin far more fundamentally than the model plant Arabidopsis does.
Rice plants with all four cytokinin receptors disabled were completely shootless — they failed to develop a shoot apical meristem and could not grow above ground at all.
The four receptors specialize: HK4 promotes seed fertility, HK3 and HK5 drive secondary branch formation in the grain head, and HK6 drives primary branch formation — each receptor controls a distinct architectural outcome.
All cytokinin-regulated gene activity in rice flows exclusively through these four receptors, even though rice carries an additional cytokinin-binding protein, suggesting no alternate signaling pathway compensates.
