Root-secreted peptide OsPEP1 regulates primary root elongation in rice

Hormone-like signaling peptides play essential roles in plant growth and development; however, few peptides regulating root development have been identified in rice (Oryza sativa). Here, we combined liquid chromatography-tandem mass spectrometry (LC-MS/MS) with whole-genome in silico screening for root-secreted peptides in rice. We identified the five-amino-acid PEPTIDE 1 (PEP1) encoded by OsPEP1 (LOC_Os11g09560). OsPEP1 was expressed highly in root tissues, especially root cap cells and epidermal cells in the root maturation zone. Exogenous application of PEP1 inhibited primary root growth. Notably, OsPEP1 RNA interference (RNAi) lines had short primary roots with small meristems and short cells in the root elongation zone; furthermore, the short root phenotype of OsPEP1 RNAi plants could be rescued by exogenous application of PEP1. Our transcriptome data further revealed that PEP1 could reprogram the expression of genes in different pathways, including oxidation-reduction. OsPEP1 overexpression lines similarly displayed short roots, although this phenotype was not rescued by exogenous PEP1. These results suggest that root growth can be inhibited by both too much and too little PEP1. Our findings highlight PEP1 as a candidate plant peptide hormone regulating root development in rice.