Impacts of Salt Stress on the Rhizosphere and Endophytic Bacterial Role in Plant Salt Alleviation

Abstract

Salinity stress is among the key challenges for sustainable food production. It is continuously increasing against the backdrop of constant climate change and anthropogenic practices leading to a huge drop in soil, water, and cultivated crop quality and productivity. Halotolerant plants represent hot spots for endophytic bacteria which may have mechanisms to overcome salt stress. This research initiative aims to highlight the possible exploitation of bacterial endophytes as a microbial biotechnology tool in the productive success of plants exposed to saline stress. We started by solely studying the mechanisms of stress tolerance by plants and halotolerant bacteria. After that, we focused on the beneficial mechanisms of endophytic bacteria in salt stress mitigation. On one side, potent bacterium works by promoting plant performances by facilitating the plant’s nutrient uptake (P, K, Zn, N, and Fe) and by promoting the production of growth hormones (IAA and CKs). On the other side, they balance stress phytohormones (ABA, JA, GA, and ACC) produced by plants in case of soil salt augmentation. The selected potent endophytic bacteria could be exploited and applied to ameliorate the production and salt tolerance of food crops. Lastly, we elucidated deeper advanced technologies including (i) genomics unveiling the plant’s culture-dependent and culture-independent microbiomes, (ii) metabolomics focusing on genes’ metabolic pathways to discover novel secondary metabolites, (iii) transcriptomics studying gene expression, and (iv) proteomics delimiting proteins expressed in stress alleviation. These technologies have been used to understand the plant–bacterial mechanisms of interaction to combat salt stress.

Potential in enhancement of salinity tolerance to crops in Vietnam’s Mekong Delta using endophytes: A review

“…Especially, there are unique populations of resident endophytic microbiota targeted within plants under saline stress. Endophytes including bacteria, fungi, archaea, and actinomycetes asscociated to host plant as potential candidates can help to counteract the stress as well as improving plant health and cultivated crops (figure 2) [3]. Regardingly, endophytes as well as plant-endophytic interaction can alleviate negative impacts of stress by accumulating and synthesizing compatible concentration of organic osmolytes and their derivatives including amino acids (such as glycine, proline, choline, glutamate, betaine, etc.…”

“…), and sugars (such as 1340 (2024) 012026 IOP Publishing doi:10.1088/1755-1315/1340/1/012026 4 trehalose, exopolysaccharides) [12]. The exopolysaccharides in endophytic bacteria form biofilms for maintaining their moisture at high Na + concentrations [3]. In addition, they can activate the antioxidant defense system and phytohormonal profiles by altering defense enzymes, indole-3-acetic acid (IAA), jasmonic acid (JA), abscisic acid (ABA), and gibberellin levels [12].…”

“…The antioxidant defence system involves in scavenging ROS directly or indirectly associated with antioxidant metabolites (such as glutathione, ascorbate, and tocopherol) and antioxidant enzymes (such as superoxide dismutases (SOD), catalases (CAT), ascorbate-or thiol-dependent peroxidases (APX), glutathione reductases (GR), dehydroascorbate reductases (DHAR) and mono-dehydroascorbate reductases (MDHAR)) [10]. The lipidic layer of Gram-negative bacteria and bacterial consortium interactions are also useful tools for saline stress mitigation [3]. Under stress, plant-endophytic interaction can regulate key transcripts to lower Na + accumulation such as high-affinity K + transporter 1 (HKT1), ethylene-responsive element binding protein (EREBP), betaine aldehyde dehydrogenase (BADH), salt overly sensitive 1 (SOS1), and CAT genes [12].…”

“…Crops under saline stress exhibited a yield loss as well as reduction in seed germination, plant growth, and plant biomass. It leads to extremely decline in agricultural production of nearly 1,128 million hectares [1][2][3]. The negative effect of salinisation is significantly being increased in the backdrop of global climate change not only in Vietnam but also worldwide in the last several decades.…”

“…Endophytes (endo, within; phyte, plant) are present in all living healthy plant species asymptomatically without any apparent symptoms or negative effects to their hosts. In addition, they show positive effects in promoting the plant growth and tolerating abiotic and biotic stresses [3,7]. In this regard, endophytes have been considered as the potential candidates promoting host plant under saline stress.…”