Antarctic Extremophiles: Biotechnological Alternative to Crop Productivity in Saline Soils

Abstract

Salinization of soils is one of the main sources of soil degradation worldwide, particularly in arid and semiarid ecosystems. High salinity results in osmotic stress and it can negatively impact plant grow and survival. Some plant species, however, can tolerate salinity by accumulating osmolytes like proline and maintaining low Na + concentrations inside the cells. Another mechanism of saline stress tolerance is the association with symbiotic microorganism, an alternative that can be used as a biotechnological tool in susceptible crops. From the immense diversity of plant symbionts, those found in extreme environments such as Antarctica seems to be the ones with most potential since they (and their host) evolved in harsh and stressful conditions. We evaluated the effect of the inoculation with a consortium of plant growth-promoting rhizobacteria (PGPB) and endosymbiotic fungi isolated from an Antarctic plant on saline stress tolerance in different crops. To test this we established 4 treatments: (i) uninoculated plants with no saline stress, (ii) uninoculated plants subjected to saline stress (200 mM NaCl), (iii) plants inoculated with the microorganism consortium with no saline stress, and (iv) inoculated plants subjected to saline stress. First, we assessed the effect of symbiont consortium on survival of four different crops (cayenne, lettuce, onion, and tomato) in order to obtain a more generalized response of this biological interaction. Second, in order to deeply the mechanisms involved in salt tolerance, in lettuce plants we measured the ecophysiological performance (F v /F m ) and lipid peroxidation to estimate the impact of saline stress on plants. We also measured proline accumulation and NHX1 antiporter gene expression (involved in Na + detoxification) to search for possible mechanism of stress tolerance. Additionally, root, shoot, and total biomass was also obtained as an indicator of productivity. Overall, plants inoculated with microorganisms from Antarctica increased the fitness related traits in several crops. In fact, three of four crops selected to assess the general response increased its survival under salt conditions compared with those uninoculated plants. On the other hand, saline stress negatively impacted all measured trait, but inoculated plants were significantly less affected. In control osmotic conditions, there were no differences in proline accumulation and lipid peroxidation between inoculation treatments. Interestingly, even in control salinity, F v /F m was higher in inoculated plants after 30 and 60 days. Under osmotic stress, F v /F m , proline accumulation and NHX1 expression was significantly higher and lipid peroxidation lower in inoculated plants compared to uninoculated individuals. Moreover, inoculated plants exposed to saline stress had a ...

Antarctic root endophytes improve physiological performance and yield in crops under salt stress by enhanced energy production and Na+ sequestration

“…The two fungal endophytes originally isolated from Antarctic plants, Penicillium chrysogenum and Penicillium brevicompactum, had previously been found responsible for increasing yield under water shortage and salinity conditions in lettuce 7,11 . Besides improving plant physiological parameters (A max and WUE), fungal endophytes also promoted the accumulation of the amino acid proline 7 , an osmotic molecule that has been previously suggested to mediate symbiont-conferred plant tolerance to water deficit 55,56 .…”

“…Under such scenarios, the physiological and biochemical functions of both wild and cultivated plant species are impaired causing severe yield losses 59 . Although it still needs to be tested at real production scales, harnessing fungal endophyte symbionts of plants appears to be a suitable strategy not only for improving crop yields but also for the design of environmentally friendly agricultural strategies 5,6,11,14 .…”

“…concentrations in vacuoles allow plants to alleviate water deficit and maintain positive carbon gain 15,17 . The Na + transport is governed by a family of genes of the NHX-type, well described in Arabidopsis thaliana but also present in other crop species 7,10,11,18 . Tomato plants are able to accumulate Na + in leaves when growing in soils with high sodium contents 19 and an increased tolerance has been observed in plants overexpressing NHX genes 20,21 .…”

“…Interestingly, in some cases these microorganisms have been found already to improve plant adaptation to stressful conditions by establishing a so-called 'functional symbiosis' 43 . Indeed, using the Antarctic plant Colobanthus quitensis as a source, we recently identified two species of Penicillium that retained their functional role observed in their native plant host even when exposed to a new plant species 7,11 . Thus, considering the geographic isolation and inhospitable conditions for growth that prevails in Antarctica and the referred ecological role of some Antarctic plant endophytes, it is highly plausible that these microorganisms may have unique metabolic pathways with an unexplored potential as biotechnological tools.…”

Horizontal Gene Transfer and Endophytes: An Implication for the Acquisition of Novel Traits

“…Moreover, comparative genomics studies suggested that these fungi display similar genomic content to their associated organism, as well as symbiosis-specific genes [105,106]. The endophytic fungi can influence the physiology of the host plant by protecting against pathogenic fungi [104,107,108], promoting plant growth [97,109,110], and aiding nutrient and water uptake [111]. Moreover, studies have demonstrated the positive impacts of plant-endophyte associations in maintaining ecological balance and their potential biotechnological applications.…”