LAUSR

Significance Regulation of growth is crucial for overall plant development and its adaptation to environment. Peptide rapid alkalinization factors 1 (RALF1) and phytohormone auxin are key growth regulators with characteristic both rapid and long-term effects. However, the underlying mechanism and coordination of these signals are unclear. Our study reveals that those two signals trigger rapid growth inhibition (<1 min) by rapidly alkalinizing the apoplast, a result of rapid net H+ influx across the plasma membrane; nonetheless, their signaling mechanisms are independent. RALF1 sustains root growth inhibition long term by inducing auxin biosynthesis and signaling. These discoveries contribute to the understanding of rapid plant growth responses and hormone-peptide cross-talk for optimization of plant growth and architecture also relevant for agriculture applications.