Mlo, a Modulator of Plant Defense and Cell Death, Is a Novel Calmodulin-binding Protein

Abstract

Transient influx of Ca2؉ constitutes an early event in the signaling cascades that trigger plant defense responses. However, the downstream components of defense-associated Ca 2؉ signaling are largely unknown. Because Ca 2؉ signals are mediated by Ca 2؉ -binding proteins, including calmodulin (CaM), identification and characterization of CaM-binding proteins elicited by pathogens should provide insights into the mechanism by which Ca 2؉ regulates defense responses. In this study, we isolated a gene encoding rice Mlo (Oryza sativa Mlo; OsMlo) using a protein-protein interactionbased screening of a cDNA expression library constructed from pathogen-elicited rice suspension cells. OsMlo has a molecular mass of 62 kDa and shares 65% sequence identity and scaffold topology with barley Mlo, a heptahelical transmembrane protein known to function as a negative regulator of broad spectrum disease resistance and leaf cell death. By using gel overlay assays, we showed that OsMlo produced in Escherichia coli binds to soybean CaM isoform-1 (SCaM-1) in a Ca 2؉ -dependent manner. We located a 20-amino acid CaMbinding domain (CaMBD) in the OsMlo C-terminal cytoplasmic tail that is necessary and sufficient for Ca 2؉ -dependent CaM complex formation. Specific binding of the conserved CaMBD to CaM was corroborated by sitedirected mutagenesis, a gel mobility shift assay, and a competition assay with a Ca 2؉ /CaM-dependent enzyme. Expression of OsMlo was strongly induced by a fungal pathogen and by plant defense signaling molecules. We propose that binding of Ca 2؉ -loaded CaM to the C-terminal tail may be a common feature of Mlo proteins.

AtBAG6, a novel calmodulin-binding protein, induces programmed cell death in yeast and plants

“…13,14,23 In this study, we screened an Arabidopsis cDNA expression library constructed from heat-treated plant seedlings using AtCaM2::HRP as a probe. 20,22 In all, 11 positive clones were obtained from a total of 5 Â 10 5 recombinant phages. Based on the restriction patterns of plasmid inserts, the genes coding for CaMBPs were classified into seven different loci.…”

“…[20][21][22] Here, we report the isolation and characterization of an Arabidopsis gene encoding a BAG protein homolog (AtBAG6). Our data indicate that AtBAG6 expression in yeast and plant cells induces cell death.…”

Genome-wide identification, characterization, and expression analysis of the MLO gene family in Cucumis sativus

“…Mildew resistance locus o (MLO) proteins belong to a unique plant-based family of seven-transmembrane domain (TM) proteins that contain a C-terminal calmodulin-binding domain (CaMBD) and an extracellularly located N-terminus (Devoto et al, 1999;Kim et al, 2002a). Recessive mutations in the MLO gene confer durable broad-spectrum resistance to all known isolates of the barley powdery mildew (PM) fungus Blumeria graminis f. sp hordei (Bgh) (Buschges et al, 1997).…”

Transcriptome and Small RNA Sequencing Analysis Revealed Roles of PaWB-Related miRNAs and Genes in Paulownia fortunei

“…The binding of the endogenous plant elicitor peptides (PEPs) to their receptors (PEPRs) located on the plasma membrane resulted in an increase of cytosolic Ca 2+ , which was the early response of the signal cascade to activate the immune response [75,76]. It also had been reported that the Ca 2+ increase played a critical role in MLO function [77]. Peterhansel et al [78] suggested that the development of MLO-mediated resistance required the involvement of two genes, ROR1 and ROR2, while MLO-mediated defense response might involve one or more small GTP-binding proteins of the ROP family [79].…”