A CLE14 Signalling Cascade Promotes Arabidopsis Root Hair Elongation

ABSTRACT The CLAVATA3 (CLV3)/EMBRYO SURROUNDING REGION‐RELATED(CLE) peptides play crucial roles in plentiful plant developmental and adaptive processes. In this study, we demonstrate that Arabidopsis CLE14 acts as a critical regulator of root hair elongation. Compared to the wild‐type (WT) plant, CRISPR/Cas9‐generated cle14‐cr mutants exhibit reduced root hair length, whereas overexpression of CLE14 promotes root hair elongation. In consistence, the synthetic CLE14 peptide also facilitates root hair elongation. However, CLE14 peptide‐induced root hair elongation is significantly compromised in clv2 and crn mutants, suggesting the requirement of CLV2 and CRN proteins in CLE14‐mediated root hair growth. Genetic and pharmacological evidence further indicates that ethylene acts downstream of CLE14‐CLV2/CRN module to regulate root hair elongation. Additionally, CLE14 peptide upregulates the expression level of RHD6 and RSL4 via EIN3 and EIL1, the key transcription factors in ethylene signalling. Subsequently, RSL4 acts downstream of RHD6 to trigger hydrogen peroxide (H 2 O 2 ) and nitric oxide (NO) accumulation by upregulating the expression of H 2 O 2 and NO biosynthesis‐related genes, ultimately driving root hair elongation. Collectively, our findings elucidate the signalling components underlying CLE14‐mediated root hair elongation.