Halomonas ventosae JPT10 promotes salt tolerance in foxtail millet (Setaria italica) by affecting the levels of multiple antioxidants and phytohormones

Recruitment of specific rhizosphere microorganisms in saline-alkali tolerant rice improves adaptation to saline-alkali stress

Increasing annual soil salinization poses a major threat to global ecological security. Soil microorganisms play an important role in improving plant adaptability to stress tolerance, however, the mechanism of saline-alkali tolerance to plants associated with rhizosphere microbiome is unclear. We investigated the composition and structure of the rhizospheric bacteria and fungi communities of the saline-alkali tolerant (Oryza sativa var. Changbai-9) and sensitive (Oryza sativa var. Kitaake) rice grown in saline-alkali and non-saline-alkali soils. The results demonstrated that the saline-alkali tolerant rice enriched the rhizosphere bacteria taxa, including Hydrogenophaga, Pseudomonas, and Aeromonas, and fungi taxa, such as Chaetomium, Cladosporium and Tausonia, which may facilitate rice growth and enhance rice saline-alkali tolerance. Saline-alkali tolerant rice reduced the Na+/K+ ratio and improved rice yield by enhancing the stability of co-occurrence network associated with recruiting bacterial and fungal keystone species. The rhizosphere bacteria of the saline-alkali tolerant rice exhibited a markedly elevated expression of functions related to the saline-alkali tolerance, including the ABC transporter and the two-component system, compared to sensitive rice under saline-alkali stress. Overall, the saline-alkali tolerant rice responds to saline-alkali stress by recruiting keystone rhizosphere microorganisms to enhance rice saline-alkali tolerance. This study provides a theoretical basis for using specific microorganisms to improve plant tolerance in saline-alkali soils.

Small peptide SiDVL/RTFLs from foxtail millet inhibit root growth through repressing auxin signaling in transgenic Arabidopsis

KEY MESSAGE

SiDVLs inhibit auxin signaling to regulate root growth by enhancing the expression of Aux/IAAs and reducing the protein accumulation of PINs. The DEVIL/ ROTUNDIFOLIA (DVL/RTFL), a small polypeptide family, is conserved in seed plants and important in regulating plant growth and development. However, the molecular mechanisms remain largely unknown. Here, 27 SiDVLs were identified in foxtail millet genome. Overexpression of three SiDVLs in Arabidopsis (Arabidopsis thaliana) strongly repressed the plant growth, especially the root growth. We demonstrate that overexpression of SiDVLs enhances Auxin/Indole-3-Acetic Acids (Aux/IAAs) transcription, thereby weakening auxin signaling in the roots. Furthermore, SiDVLs reduced the protein levels of the auxin transporters PIN-formed 1 (PIN1), PIN2, and PIN7 in the roots. The impaired auxin signaling reduces the cell division and elongation. In conclusion, SiDVLs suppress cell division and elongation in root by inhibiting auxin signaling and transport, which lead to the reduced root growth.

Halotolerant Bacillus sp. strain RA coordinates myo-inositol metabolism to confer salt tolerance to tomato

Soil salinity is a worldwide problem threatening crop yields. Some plant growth-promoting rhizobacteria (PGPR) could survive in high salt environment and assist plant adaptation to stress. Nevertheless, the genomic and metabolic features, as well as the regulatory mechanisms promoting salt tolerance in plants by these bacteria remain largely unknown. In the current work, a novel halotolerant PGPR strain, namely, Bacillus sp. strain RA can enhance tomato tolerance to salt stress. Comparative genomic analysis of strain RA with its closely related species indicated a high level of evolutionary plasticity exhibited by strain-specific genes and evolutionary constraints driven by purifying selection, which facilitated its genomic adaptation to salt-affected soils. The transcriptome further showed that strain RA could tolerate salt stress by balancing energy metabolism via the reprogramming of biosynthetic pathways. Plants exude a plethora of metabolites that can strongly influence plant fitness. The accumulation of myo-inositol in leaves under salt stress was observed, leading to the promotion of plant growth triggered by Bacillus sp. strain RA. Importantly, myo-inositol serves as a selective force in the assembly of the phyllosphere microbiome and the recruitment of plant-beneficial species. It promotes destabilizing properties in phyllosphere bacterial co-occurrence networks, but not in fungal networks. Furthermore, interdomain interactions between bacteria and fungi were strengthened by myo-inositol in response to salt stress. This work highlights the genetic adaptation of RA to salt-affected soils and its ability to impact phyllosphere microorganisms through the adjustment of myo-inositol metabolites, thereby imparting enduring resistance against salt stress in tomato.

Halophilic Plant-Associated Bacteria with Plant-Growth-Promoting Potential

The salinization of soils is a growing agricultural concern worldwide. Irrigation practices, drought, and climate change are leading to elevated salinity levels in many regions, resulting in reduced crop yields. However, there is potential for a solution in the microbiome of halophytes, which are naturally salt-tolerant plants. These plants harbor a salt-tolerant microbiome in their rhizosphere (around roots) and endosphere (within plant tissue). These bacteria may play a significant role in conferring salt tolerance to the host plants. This leads to the possibility of transferring these beneficial bacteria, known as salt-tolerant plant-growth-promoting bacteria (ST-PGPB), to salt-sensitive plants, enabling them to grow in salt-affected areas to improve crop productivity. In this review, the background of salt-tolerant microbiomes is discussed and their potential use as ST-PGPB inocula is explored. We focus on two Gram-negative bacterial genera, Halomonas and Kushneria, which are commonly found in highly saline environments. These genera have been found to be associated with some halophytes, suggesting their potential for facilitating ST-PGPB activity. The study of salt-tolerant microbiomes and their use as PGPB holds promise for addressing the challenges posed by soil salinity in the context of efforts to improve crop growth in salt-affected areas.