The phrase “to be worth one’s salt” speaks to the importance with which this mineral was held by ancient peoples, as—in addition to its flavour-enhancing properties—it was the crucial factor allowing food preservation in the absence of refrigeration or canning technologies. However, the same microbe-killing properties that make it so useful in food preservation also wreak havoc with animal and plant physiology. In fact, conquerors of the historic Near East, wishing to destroy a vanquished territory entirely, would “salt the earth” after battle to ensure no crops would grow for years to come. Today, saline soils remain a harmful stress to be navigated by plants growing in a variety of ecosystems and a critical issue limiting global agricultural production. The manner in which salt stress impacts a plant is manifold, affecting a spectrum of processes from the molecular- to whole-organism level. This necessitates a complex and strategic stress response from the plant to coordinate stress perception with the extensive transcriptional remodelling required to ensure recovery and enhanced salinity tolerance.
For the month of December, Physiologia Plantarum is exploring a variety of transcriptional and post-transcriptional mechanisms regulating salt tolerance in plants. To mark this release, we will be highlighting a number of articles to offer a cross-section of the different approaches used to examine this critical issue.
Recent advances in high-throughput sequencing technologies have made the prospect of cataloguing entire genomes cheaper, faster, and more comprehensive than ever before. With these benefits come new opportunities to: (1) re-sequence the genomes of important model species – providing a more complete picture of intra-species genomic variation, which could lead to the detection of genetic factors linked to desirable agronomic traits; and (2) the sequencing of wild relatives of crucial crop species, allowing for the identification of novel processes involved in stress tolerance that may be of utility to domesticated relatives. In this Special Issue of Physiologia Plantarum, we have two examples (Bansal et al. and Rajkumar et al.) where DNA sequencing has been strategically deployed to reveal hidden genomic insights related to salt tolerance in two important crop species.
While genomics provides us with an (almost) complete survey of an organism’s collection of genes, the field of transcriptomics is concerned with the study of how these genes are expressed into RNA transcripts—the molecular intermediary that bridges the gap between a gene and the functional protein it encodes. By monitoring the abundance of all the RNA in a cell or tissue simultaneously, researchers can capture functional insights into the dynamic way the genome is utilised at a given developmental stage or in response to a specific stress. This can identify the molecular roadmaps used by plants when faced with particular hardships, and help guide future efforts to manage plants growing in challenging environments. In this Special Issue of Physiologia Plantarum, we have a selection of studies utilising transcriptomic approaches to assess the different mechanisms regulating salt tolerance in plants (Munsif et al., Vita et al., Basu & Roychoudhury, Frosi et al., Cartagena et al.)
Armed with the global insights gained from genomic and transcriptomic studies, researchers can strategically zero in on genes of interest using reverse genetic approaches to assess their involvement in plant metabolism or in an array of desirable plant traits. Reverse genetics is a method of characterising a gene’s function by disrupting its genetic code and assessing the changes that manifest in the organism’s observable characteristics or traits (its phenotype). This practice has been utilised to great effect for more than three decades and has been pivotal in bridging the gap between vast banks of DNA sequencing data and real-world functional implications—especially when used in conjunction with other characterisation tools, such as metabolomics, which can reveal profound changes in the complement of plant metabolites attributable to the altered gene of interest. Today, the speed and precision of these approaches have increased tremendously and in this Special Issue of Physiologia Plantarum we have a selection of studies that have made use of reverse genetics and metabolomics to functionally characterise genes with vital roles in transcriptional and post-transcriptional regulation of salt tolerance in plants (Ram et al., Jain & Garg, Agarwal et al., Divya et al., Naguib et al., Marriboina et al., Tak et al.)
Soil is not simply an inert medium to be mined by plants for water and nutrients, but a complex environment teeming with microbial life, such as fungi, protozoa, bacteria, and viruses. The microbial communities that thrive within plant roots and the surrounding soil—collectively termed the root microbiome—are populated with both friends and enemies; with some microbes serving crucial functions degrading complex organic matter and cycling nutrients into plant-accessible forms, while others are cause of devastating plant diseases. As such, plants have developed sophisticated mechanisms with which to navigate these complex interactions—rapidly identifying and dispatching harmful pathogens, or altering their own anatomy and physiology to nurture and accommodate beneficial microbes. Recent research has begun to shed light on the interesting ways the root microbiome can impact a plant’s ability to tolerate environmental stresses, such as salinity. These can take a variety of forms, such as triggering the plant to manufacture osmoprotectants (dehydration-resisting molecules that accumulate within the plant cell), targeted regulation of specific proteins involved with transporting ions (such as salt) across cell membranes, and promoting the activity of enzymes that can neutralise harmful free radicals that are produced in abundance during salt stress. In this Special Issue of Physiologia Plantarum, Roy et al. (2021) explore the hidden world of the root microbiome and the vital role it plays in bolstering salt tolerance in plants