Manipulation of Calcium Ion Influx—Mediated Immune Signaling Systems for Crop Disease Management

Abstract

Calcium ion is the principal mediator in plant immune signaling system. Ca2+ signaling system involves calcium signatures, which result from the concerted action of voltage-dependent Ca2+-permeable ion channels, cyclic nucleotide-gated channels, glutamate receptor-like ion channels, calcium transporters, calcium ion pumps, carriers, and Ca2+ efflux channels, The Ca2+ signaling system involves Ca2+ sensors. Calmodulins (CaMs) and CaM-like proteins (CMLs) are calcium sensors. Cellular Ca2+ signals are decoded and transmitted by Ca2+ binding proteins that relay this information into downstream responses. Calcium-dependent protein kinases (CDPKs) perceive Ca2+ signals nd relay them into specific phosphorylation events to induce downstream defense responses. Early and rapid induction of Ca2+ signaling system has been shown to be necessary for switching on host defense responses to prevent the invading pathogen development. Manipulation of even one component in the Ca2+ signaling system may be able to trigger the entire gamut of immune response signaling systems to confer resistance against a wide-spectrum of pathogens. G-proteins are involved in initiating Ca2+ influx. Genes encoding G-proteins have been cloned and used for engineering to develop disease resistant plants. Bioengineering gene encoding glutamate receptor-like ion channel protein has been found to be a useful technology to develop disease resistant plants. Manipulation of the H+-ATPase proton pump has been shown to be a potential tool for management of crop diseases. The enzyme transports one H+ in exchange of one K+. The K+/H+ exchange response may be mediated by Ca2+ influx. The algal elicitor laminarin manipulates the proton pump and triggers defense responses. Several commercial formulations of laminarin have been developed to control oomycete, fungal, and bacterial pathogens in monocot and dicot plants. Chitosan formulations inactivate H+-ATPase resulting in membrane depolarization, which is involved in increasing Ca2+ influx. Chitosan effectively controls various oomycete, fungal, bacterial and viral diseases. Plant annexins are capable of mediating passive, channel-like Ca2+ transport and Ca2+influx. Transgenic plants ectopically expressing annexin gene show enhanced disease resistance. Calmodulin (CaM) is a Ca2+ sensor protein and several disease-resistant plants have been developed by engineering calmodulin genes. Engineering calmodulin-binding proteins also have been shown to be effective in developing disease-resistant plants. Calcium-dependent protein kinases (CDPKs) are Ca2+ sensor proteins in transducing differential Ca2+ signatures activating complex downstream responses. Disease resistant plants against wide range of pathogens could be developed using CDPK genes. Thiamine (vitamin B1) is involved in priming of plants to induce disease resistance. It provides long-lasting protection against pathogens. Thiamine triggers Ca2+ influx-dependent signaling pathway. Thus, manipulation of Ca2+-influx-dependent signaling pathways is a potential tool for management of various crop diseases.