# Regulation of stomatal development by receptor-like kinases and receptor-like proteins in Arabidopsis and grasses

## TL;DR

This paper reviews how receptor-like kinases and proteins regulate stomatal development in plants like Arabidopsis and grasses, focusing on signaling pathways and key genes.

## Contribution

The paper provides a comprehensive review of stomatal receptor mechanisms, emphasizing LRR-RLKs and unresolved questions like ligand recognition.

## Key findings

- LRR-RLKs and LRR-RLPs, including TMM, ERf, and SERK, regulate stomatal patterning through the YDA-MAPK cascade and SPCH inhibition.
- HSL1 interacts with SERK co-receptors and responds to CLE9/10 ligands, while ligands for CLV1 and MUS remain unknown.
- Maize PAN1 and PAN2 are crucial for subsidiary cell formation, but their ligands are still uncharacterized.

## Abstract

Stomata are core channels for plant gas exchange and water transpiration, and precise regulation of their development directly impacts photosynthetic efficiency, water use, and stress resistance. Plant receptor kinases, particularly leucine-rich repeat receptor-like kinases (LRR-RLKs), function as key signal sensors: they perceive endogenous and exogenous signals, trigger downstream cascades, and finely regulate stomatal initiation, differentiation, and patterning. Deciphering these mechanisms is therefore critical for improving crop stomatal traits, stress tolerance, and yield. Among receptors regulating stomatal development, LRR-RLKs and leucine-rich repeat receptor-like proteins (LRR-RLPs) are the best studied. Too Many Mouths (TMM), the first identified stomatal receptor (LRR-RLP), forms a multiprotein complex with ERECTA family (ERf) and SERK family LRR-RLKs. This complex recognizes Epidermal Patterning Factors (EPFs)/EPF-like factors (EPFLs) peptides., activates the YODA (YDA)-MAPK cascade, and inhibits the key stomatal lineage transcription factor SPEECHLESS (SPCH), thereby precisely regulating stomatal patterning and differentiation in Arabidopsis. Beyond this core complex, other LRR-RLKs (e.g., HSL1, CLV1, MUS) also regulate Arabidopsis stomatal development or morphogenesis. HSL1 recruits SERK co-receptors and perceives CLE9/10 ligands, but the ligands for CLV1 and MUS in stomatal development remain unknown. Notably, maize PAN1 and PAN2 are essential for asymmetric division of subsidiary mother cells (SMCs) and subsidiary cell (SC) formation, with their cognate ligands also uncharacterized. This review summarizes key advances in stomatal receptor (especially LRR-RLK) mediated stomatal development in Arabidopsis and grasses and highlights core issues such as ligand recognition.