Host Resistance Signaling Network System to Multiple Stresses

Abstract

Cruciferous plants have developed numerous molecular mechanisms to respond to various environmental and multiple biotic and abiotic stresses. Whenever plant encounters any kind of stress, first of all there is perception of the signals by the potential sensors. This further generates secondary messengers (e.g., ABA, ROS, Ca²⁺, inositol phosphates). The secondary messengers can alter the levels of intracellular Ca²⁺. Any change in cytoplasmic Ca²⁺ is sensed by Ca²⁺ sensors, i.e., calcium binding proteins, and after interacting with corresponding interacting partners they initiate a protein phosphorylation cascade. This signaling cascade ultimately regulates the transcription factors that manage specific suite of stress-regulated genes and the functional proteins involved in protecting the cell against stress. The expression of stress-regulated genes leads to the production of various kinds of regulatory molecules like the phytohormones ABA, ET, and SA, transcription factors, etc. A second round of signaling can get started by these regulatory molecules which may further enhance the initial signaling pathway. These signaling networks are very complex and interconnected at many levels for transferring information to generate robust host resistance. Moreover, during signaling other components are also involved. A successful signal transduction pathway demands proper coordination of all signaling molecules. This is brought about by specific molecules whose functions are to transport, bring together, or modify the signaling molecules. They themselves are not involved in relaying the signal. These proteins consist of scaffolding proteins, protein modifiers (e.g., enzymes needed for protein glycosylation, methylation, ubiquitination, and lipidation), and adaptors. Cruciferous interactions with multiple stresses trigger a wide range of defense reactions at molecular and cellular levels to ensure that host cells are insulated from these challenges they encounter. The production of ROS, MAP Kinase cascades, and hormone signaling are triggered by multiple stresses and play crucial roles as common components of the host immune system. GbRLK, a receptor like kinase (RLK) gene, is involved in response to multiple stresses as positive regulator Transcription factors (TFs) are the central core of the genes as defense signaling pathways to multiple stress. MYB TFs play essential roles in multiple stress responses. ATAF1 is a multi-faceted TF with versatile capabilities and plays an important role in mediating crosstalk between multiple stress responses. HSPs gene regulate the function of NBS-LRR genes in response to multiple stresses. miRNAs may target only one locus or several loci in response to multiple stresses. Cell signaling in response to multiple stresses largely depends on the SnRK family of protein kinases in plants. Calcium is a key signaling pathway in host responses to multiple stresses through calcium sensor proteins like calcineurin-B-like protein (CBls), the calmodulin (CaM), and calmodulin-like protein (CMLs).

Transcriptome analyses based on microarrays and proteomic studies have given rise to rapid progress in the field of plant signal transduction and gene regulation. Gene Chip and cDNA microarrays together with massive whole genome sequencing proved to be useful in identifying novel signaling determinants on a whole-genome scale in response to various stresses. This has increased our understanding towards the complex mechanisms involved in various aspects of plant responses to environmental cues. Proteomics approach is useful in studying post-translational modifications of the proteins. It can also be used to clone unique genes by means of differential analysis which will expedite our understanding of stress signaling mechanisms in plants. Therefore, stress-tolerant plants can be genetically engineered by the combined efforts of plant molecular biologists, physiologists, and breeders.