PbrRALF2-elicited reactive oxygen species signaling is mediated by the PbrCrRLK1L13-PbrMPK18 module in pear pollen tubes

Xiaobing Kou; Jiangmei Sun; Peng Wang; Danqi Wang; Peng Cao; Jing Lin; Youhong Chang; Shaoling Zhang; Juyou Wu

doi:10.1038/s41438-021-00684-y

PbrRALF2-elicited reactive oxygen species signaling is mediated by the PbrCrRLK1L13-PbrMPK18 module in pear pollen tubes

Hortic Res. 2021 Oct 4;8(1):222. doi: 10.1038/s41438-021-00684-y.

Authors

Xiaobing Kou^#¹, Jiangmei Sun^#¹, Peng Wang^#¹, Danqi Wang¹, Peng Cao¹, Jing Lin², Youhong Chang², Shaoling Zhang¹, Juyou Wu^{3

4}

Affiliations

¹ Center of Pear Engineering Technology Research, State Key Laboratory of Crop Genetics and Germplasm Enhancement, College of Horticulture, Nanjing Agricultural University, 210095, Nanjing, China.
² Jiangsu Key Laboratory for Horticultural Crop Genetic Improvement, 210014, Nanjing, China.
³ Center of Pear Engineering Technology Research, State Key Laboratory of Crop Genetics and Germplasm Enhancement, College of Horticulture, Nanjing Agricultural University, 210095, Nanjing, China. juyouwu@njau.edu.cn.
⁴ Jiangsu Key Laboratory for Horticultural Crop Genetic Improvement, 210014, Nanjing, China. juyouwu@njau.edu.cn.

^# Contributed equally.

Abstract

Rapid alkalinization factors (RALFs) are cysteine-rich peptides that play important roles in a variety of biological processes, such as cell elongation and immune signaling. Recent studies in Arabidopsis have shown that RALFs regulate pollen tube growth via plasma membrane receptor-like kinases (RLKs). However, the downstream signal transduction mechanisms of RLKs in pollen tubes are unknown. Here, we identified PbrRALF2, a pear (Pyrus bretschneideri) pollen RALF peptide that inhibits pollen tube growth. We found that PbrRALF2 interacts with a malectin-like domain-containing RLK, PbrCrRLK1L13. The relative affinity between PbrRALF2 and PbrCrRLK1L13 was at the submicromolar level, which is consistent with the values of ligand-receptor kinase pairs and the physiological concentration for PbrRALF2-mediated inhibition of pollen tube growth. After binding to its extracellular domain, PbrRALF2 activated the phosphorylation of PbrCrRLK1L13 in a dose-dependent manner. We further showed that the MAP kinase PbrMPK18 is a downstream target of PbrCrRLK1L13 that mediates PbrRALF2-elicited reactive oxygen species (ROS) production. The excessive accumulation of ROS inhibits pollen tube growth. We show that MPK acts as a mediator for CrRLK1L to stimulate ROS production, which might represent a general mechanism by which RALF and CrRLK1L function in signaling pathways.