Understanding the potential of root microbiome influencing salt‐tolerance in plants and mechanisms involved at the transcriptional and translational level

Abstract

Soil salinity severely affects plant growth and development and imparts inevitable losses to crop productivity. Increasing the concentration of salts in the vicinity of plant roots has severe consequences at the morphological, biochemical, and molecular levels. These include loss of chlorophyll, decrease in photosynthetic rate, reduction in cell division, ROS generation, inactivation of antioxidative enzymes, alterations in phytohormone biosynthesis and signaling, and so forth. The association of microorganisms, viz. plant growth‐promoting rhizobacteria, endophytes, and mycorrhiza, with plant roots constituting the root microbiome can confer a greater degree of salinity tolerance in addition to their inherent ability to promote growth and induce defense mechanisms. The mechanisms involved in induced stress tolerance bestowed by these microorganisms involve the modulation of phytohormone biosynthesis and signaling pathways (including indole acetic acid, gibberellic acid, brassinosteroids, abscisic acid, and jasmonic acid), accumulation of osmoprotectants (proline, glycine betaine, and sugar alcohols), and regulation of ion transporters (SOS1, NHX, HKT1). Apart from this, salt‐tolerant microorganisms are known to induce the expression of salt‐responsive genes via the action of several transcription factors, as well as by posttranscriptional and posttranslational modifications. Moreover, the potential of these salt‐tolerant microflora can be employed for sustainably improving crop performance in saline environments. Therefore, this review will briefly focus on the key responses of plants under salinity stress and elucidate the mechanisms employed by the salt‐tolerant microorganisms in improving plant tolerance under saline environments.

Imperative role of trehalose metabolism and trehalose‐6‐phosphate signaling on salt stress responses in plants

“…Trehalose is critical in maintaining the osmotic equilibrium in plants exposed to salt stress (Roy et al, 2021). Plants have developed mechanisms by which they can perceive sugar fluxes, known as sugar sensing, and by which they control sugar‐mediated responses, allowing them to adapt their activity at the cellular level based on sugar status and maintain homeostasis (Lecourieux et al, 2014).…”

“…When salt exposure is paired with other forms of environmental stress, the transcriptome is dramatically different than when salt stress is administered alone, demonstrating widespread interaction between the salt stress signaling pathway and other stress signaling pathways and metabolic signaling pathway (Rasmussen et al, 2013). One of the necessities for any plant to acclimatize to saline conditions depends upon its ability to maintain the balance of ions inside the plant cells (Roy et al, 2021). Trehalose and its intermediate molecules are critical in salt stress signaling and control because they activate the required salt‐responsive systems in plants, which are explored in detail in the following sections.…”

Biosynthetic Mechanisms of Secondary Metabolites Promoted by the Interaction Between Endophytes and Plant Hosts

“…and the specificity of the host cell surface receptor molecules PRR identification ( Newman et al, 2013 ). Under current conditions, although it is known that symbiosis with endophytes endows hosts with additional defense mechanisms, little is known about this aspect ( Eid et al, 2021 ; Roy et al, 2021 ). In fact, plant immune system activation and mechanical changes are the result of ongoing molecular dialogue with endophytes, a common example of which is the JA pathway discussed above ( Gutjahr, 2014 ; Pozo et al, 2015 ; Bastias et al, 2017 ).…”

Transcriptomic and Metabolomic Analysis of the Effects of Exogenous Trehalose on Salt Tolerance in Watermelon (Citrullus lanatus)

“…One of the necessary conditions for plant to adapt to salty environment is its ability to maintain the balance of ions in plant cells [ 13 ]. Trehalose and its intermediate molecules can activate the necessary salt response system in plants, maintain osmotic pressure of cells, protect membrane structure, participate in signal transduction process, and effectively protect biomolecular structure of plants, thereby maintaining metabolic balance in plants [ 14 , 15 , 16 , 17 ].…”