Peptide signaling in plants: finding partners is the key

Rice small secreted peptide, OsRALF26, recognized by FERONIA-like receptor 1 induces immunity in rice and Arabidopsis

Rapid alkalinization factors (RALFs), belonging to a family of small secreted peptides, have been considered as important signaling molecules in diverse biological processes, including immunity. Current studies on RALF-modulated immunity mainly focus on Arabidopsis, but little is reported in crop plants. The rice immune receptor XA21 confers immunity to the bacterial blight pathogen, Xanthomonas oryzae pv. oryzae (Xoo). Here, we pursued functional characterization of rice RALF26 (OsRALF26) up-regulated by Xoo during XA21-mediated immune response. When applied exogenously as a recombinant peptide, OsRALF26 induced a series of immune responses, including pathogenesis-related genes (PRs) induction, reactive oxygen species (ROS) production, and callose deposition in rice and/or Arabidopsis. Transgenic rice and Arabidopsis overexpressing OsRALF26 exhibited significantly enhanced resistance to Xoo and Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), respectively. In yeast two-hybrid, pull-down assays, and co-immunoprecipitation analyses, rice FER-like receptor 1 (OsFLR1) was identified as a receptor of OsRALF26. Transient expression of OsFLR1 in Nicotiana benthamiana leaves displayed significantly increased ROS production and callose deposition after OsRALF26 treatment. Together, we propose that OsRALF26 induced by Xoo in an XA21-dependent manner is perceived by OsFLR1 and may play a novel role in the enforcement of XA21-mediated immunity.

A screening of inhibitors targeting the receptor kinase FERONIA reveals small molecules that enhance plant root immunity

Receptor-like kinases (RLKs) constitute the largest receptor family involved in the regulation of plant immunity and growth, but small-molecule inhibitors that target RLKs to improve agronomic traits remain unexplored. The RLK member FERONIA (FER) negatively regulates plant resistance to certain soil-borne diseases that are difficult to control and cause huge losses in crop yields and economy. Here, we identified 33 highly effective FER kinase inhibitors from 1494 small molecules by monitoring FER autophosphorylation in vitro. Four representative inhibitors (reversine, cenisertib, staurosporine and lavendustin A) inhibited the kinase activity of FER and its homologues in several crops by targeting the conserved ATP pocket in the kinase structure. FER contributes to the physiological impact of representative inhibitors in plants. The treatment of roots with reversine, staurosporine and lavendustin A enhanced innate immunity in plant roots and thus alleviated soil-borne diseases in tobacco, tomato and rice without growth penalties. Consistently, RNA sequencing assays showed that lavendustin A and reversine exert profound impacts on immunity-related gene expression. Our results will set a new milestone in the development of the plant RLK kinase regulation theory and provide a novel strategy for the prevention and control of plant soil-borne diseases without growth penalties.

Function of Protein Kinases in Leaf Senescence of Plants

Leaf senescence is an evolutionarily acquired process and it is critical for plant fitness. During senescence, macromolecules and nutrients are disassembled and relocated to actively growing organs. Plant leaf senescence process can be triggered by developmental cues and environmental factors, proper regulation of this process is essential to improve crop yield. Protein kinases are enzymes that modify their substrates activities by changing the conformation, stability, and localization of those proteins, to play a crucial role in the leaf senescence process. Impressive progress has been made in understanding the role of different protein kinases in leaf senescence recently. This review focuses on the recent progresses in plant leaf senescence-related kinases. We summarize the current understanding of the function of kinases on senescence signal perception and transduction, to help us better understand how the orderly senescence degeneration process is regulated by kinases, and how the kinase functions in the intricate integration of environmental signals and leaf age information.

A wheat/rye polymorphism affects seminal root length and yield across different irrigation regimes

The introgression of a small segment of wheat (Triticum aestivum L.) chromosome arm 1BS in the distal region of the rye (Secale cereale L.) 1RS.1BL arm translocation in wheat (henceforth 1RSRW) was previously associated with reduced grain yield, carbon isotope discrimination, and stomatal conductance, suggesting reduced access to soil moisture. Here we show that lines with the normal 1RS arm have longer roots than lines with the 1RSRW arm in both field and hydroponic experiments. In the 1RSRW lines, differences in seminal root length were associated with a developmentally regulated arrest of the root apical meristem (RAM). Approximately 10 d after germination, the seminal roots of the 1RSRW plants showed a gradual reduction in elongation rate, and stopped growing a week later. Seventeen days after germination, the roots of the 1RSRW plants showed altered gradients of reactive oxygen species and emergence of lateral roots close to the RAM, suggesting changes in the root meristem. The 1RSRW lines also showed reduced biomass (estimated by the normalized difference vegetation index) and grain yield relative to the 1RS lines, with larger differences under reduced or excessive irrigation than under normal irrigation. These results suggest that this genetic variation could be useful to modulate root architecture.

In Silico Prediction of Ligand-Binding Sites of Plant Receptor Kinases Using Conservation Mapping

Plasma membrane-bound plant receptor-like kinases (RLKs) can be categorized based on their ligand-binding extracellular domain. The largest group encompasses RLKs having ectodomains with leucine-rich repeats (LRRs). The LRR-RLKs can further be assigned to classes mainly based on the number of LRRs. Many of the receptors of the classes X and XI with more than 20 LRRs are activated by small secreted peptide ligands. To understand how peptide signaling works, it is of interest to identify the amino acids of the receptor that are directly involved in ligand interaction. Such residues have most likely been conserved over evolutionary time and can therefore be predicted to be conserved in receptor orthologues of different plant species. Here we present an in silico method to identify such residues. This involves a simplified method for identification of orthologues and a web-based program for identifying the most conserved amino acids aside from the leucines that structure the ectodomain. The method has been validated for the LRR-RLKs HAESA (HAE) and PHYTOSULFOKINE RECEPTOR1 (PSKR1) for which conservation-mapping results closely matched recent structure-based identification of ligand and co-receptor-interacting residues.