No abstract

Plant receptor-like kinases (RLKs) are involved in nearly all aspects of plant life including growth, development and stress response. Recent studies show that FERONIA (FER), a CrRLK1L subfamily member, is a versatile regulator of cell expansion and serves as a signaling node mediating cross-talk among multiple phytohormones. As a receptor for the RALF (Rapid Alkalinization Factor) peptide ligand, FER triggers a downstream signaling cascade that leads to a rapid cytoplasmic calcium increase and inhibition of cell elongation in plants. Moreover, FER recruits and activates small G proteins through the guanine nucleotide exchange factor-Rho-like GTPase (GEF-ROP) network to regulate both auxin and ABA responses that cross-talk with the RALF signaling pathway. One of the downstream processes is NADPH oxidase-dependent ROS (reactive oxygen species) production that modulates cell expansion and responses to both abiotic and biotic stress responses. Intriguingly, some pathogenic fungi produce RALF-like peptides to activate the host FER-mediated pathway and thus increase their virulence and cause plant disease. Studies so far indicate that FER may serve as a central node of the cell signaling network that integrates a number of regulatory pathways targeting cell expansion, energy metabolism and stress responses. This review focuses on recent findings and their implications in the context of FER action as a modulator that is crucial for hormone signaling and stress responses.

Plants perceive various external and internal signals to self-modulate biological processes through members of the receptor-like kinase (RLK) family, among which Catharanthus roseus receptor-like kinase 1-like ( Cr RLK1L) proteins with their ligands, rapid alkalinization factor (RALF) peptides, have attracted considerable interest. FERONIA (FER), a Cr RLK1L member, was initially reported to act as a major plant cell growth modulator in distinct tissues. Subsequently, the RALF–FER pathway was confirmed to function as an essential regulator of plant stress responses, including but not limited to immune responses. Furthermore, the RALF–FER pathway modulates immune responses and cell growth in a context-specific manner, and the vital roles of this pathway are beginning to be appreciated in crop species. The recent remarkable advances in understanding the functions and molecular mechanisms of the RALF–FER pathway have also raised many interesting questions that need to be answered in the future. This review mainly focuses on the roles of FER and other Cr RLK1L members in modulating immune responses in the context of cell growth in response to their RALF peptide ligands and presents a brief outlook for future research.

Soybean [Glycine max (L.) Merr. ] is one of the most strategical oilseed crops that provides sustainable source of protein and oil worldwide. Cultivation of soybean is severely affected by root-knot nematode (RKN). However, the mechanism of RKN parasitism to soybeans is largely unknown. In this study, we identify GmLMM1, which encodes a homolog of FERONIA-like receptor kinase in soybean, as a susceptible gene toward nematode. Mutations of GmLMM1 exhibit enhanced resistance against the RKN Meloidogyne incognita. RNA-sequencing (RNA-seq) analysis reveals a similar differential expression pattern for genes regulated by GmLMM1 (Gmlmm1 vs. wild-type) and M. incognita (M. incognita vs. mock), supporting the role of GmLMM1 in M. incognita infection. Unlike FERONIA in Arabidopsis, GmLMM1 specifically binds to MiRALF1 and AtRALF23 that suppress plant immunity, but not MiRALF3 and AtRALF1. Moreover, we found that the single-nucleotide polymorphism (SNP) in GmLMM1 leads to the natural resistance against RKNs in soybeans. Collectively, these findings uncover GmLMM1 as a susceptible target of nematode RALF-like 1 and provide new genetic resource for nematode resistant breeding.