# A Trypsin‐Like Serine Protease ZmNAL1a Fine‐Tunes Maize Floral Transition and Flowering Time

## TL;DR

A new protein in corn, ZmNAL1a, helps control when plants start to flower by moving signals from leaves to the growing tip and changing gene activity.

## Contribution

ZmNAL1a is identified as a novel diffusible signal regulating maize flowering through epigenetic and transcriptional mechanisms.

## Key findings

- ZmNAL1a moves from leaves to the shoot apical meristem to regulate floral transition.
- ZmNAL1a degrades REL2, a corepressor, to enhance flowering gene expression via histone acetylation.
- Mutation of ZmNAL1a delays flowering and suppresses key flowering gene expression.

## Abstract

The floral transition is a crucial phase in flowering plants that initiates reproductive development. Florigen, a key regulator of this transition, is expressed in the leaves and transmits environmental signals by trafficking to the vegetative shoot apical meristem, thereby promoting the floral transition. However, whether additional signals, expressed outside the meristem, control the flowering transition remains to be explored. This study identified another floral transition signal, ZmNAL1a, which encodes a trypsin‐like serine protease and can move from the leaf to the shoot apical meristem via plasmodesmata to regulate floral transition in maize. Mutation of ZmNAL1a suppresses the expression of key flowering genes in the shoot apical meristem, resulting in a delayed floral transition and flowering. ZmNAL1a interacts with and degrades RAMOSA1 ENHANCER LOCUS2 (REL2), a TOPLESS‐like corepressor, which can regulate the expression of flowering genes by affecting histone acetylation and transcriptional regulation alongside ZmEREBP147, an AP2/EREBP transcription factor. These findings suggest that ZmNAL1a is a diffusible signal that regulates the floral transition and flowering via a conserved NAL1‐TOPLESS epigenetic regulation module and through transcriptional regulation. This discovery broadens the understanding of flowering control, offering potential targets for improving adaptation and crop yield through precise manipulation of flowering time.

This study identifies a trypsin‐like serine protease, ZmNAL1a, that moves from leaves to the shoot apical meristem. ZmNAL1a promotes the floral transition by degrading TOPLESS‐like corepressor REL2, which thereby enhances the expression of key flowering genes through elevating histone acetylation and relieving REL2–ZmEREBP147‐mediated transcriptional repression. Our findings reveal a novel diffusible signal that regulates flowering time.