Predatory protists reduce bacteria wilt disease incidence in tomato plants.

Soil organisms are affected by the presence of predatory protists. However, it remains poorly understood how predatory protists can affect plant disease incidence and how fertilization regimes can affect these interactions. Here, we characterise the rhizosphere bacteria, fungi and protists over eleven growing seasons of tomato planting under three fertilization regimes, i.e conventional, organic and bioorganic, and with different bacterial wilt disease incidence levels. We find that predatory protists are negatively associated with disease incidence, especially two ciliophoran Colpoda OTUs, and that bioorganic fertilization enhances the abundance of predatory protists. In glasshouse experiments we find that the predatory protist Colpoda influences disease incidence by directly consuming pathogens and indirectly increasing the presence of pathogen-suppressive microorganisms in the soil. Together, we demonstrate that predatory protists reduce bacterial wilt disease incidence in tomato plants via direct and indirect reductions of pathogens. Our study provides insights on the role that predatory protists play in plant disease, which could be used to design more sustainable agricultural practices.

Protists as main indicators and determinants of plant performance.

BACKGROUND: Microbiomes play vital roles in plant health and performance, and the development of plant beneficial microbiomes can be steered by organic fertilizer inputs. Especially well-studied are fertilizer-induced changes on bacteria and fungi and how changes in these groups alter plant performance. However, impacts on protist communities, including their trophic interactions within the microbiome and consequences on plant performance remain largely unknown. Here, we tracked the entire microbiome, including bacteria, fungi, and protists, over six growing seasons of cucumber under different fertilization regimes (conventional, organic, and Trichoderma bio-organic fertilization) and linked microbial data to plant yield to identify plant growth-promoting microbes. RESULTS: Yields were higher in the (bio-)organic fertilization treatments. Soil abiotic conditions were altered by the fertilization regime, with the prominent effects coming from the (bio-)organic fertilization treatments. Those treatments also led to the pronounced shifts in protistan communities, especially microbivorous cercozoan protists. We found positive correlations of these protists with plant yield and the density of potentially plant-beneficial microorganisms. We further explored the mechanistic ramifications of these relationships via greenhouse experiments, showing that cercozoan protists can positively impact plant growth, potentially via interactions with plant-beneficial microorganisms including Trichoderma, the biological agent delivered by the bio-fertilizer. CONCLUSIONS: We show that protists may play central roles in stimulating plant performance through microbiome interactions. Future agricultural practices might aim to specifically enhance plant beneficial protists or apply those protists as novel, sustainable biofertilizers. Video abstract.

Effects of foliar application of amino acid liquid fertilizers, with or without Bacillus amyloliquefaciens SQR9, on cowpea yield and leaf microbiota.

Leaf surface fertilization with liquid fertilizer produced from amino acids constitutes a potentially important source of nitrogen and is important for plant production. However, few reports have focused on the plant growth promotion by novel liquid fertilizers created by new amino acid resources, let alone the influence on leaf microbiota. In this study, the effects of liquid fertilizer, created by amino acids hydrolyzed from animal hairs with or without the PGPR strain Bacillus amyloliquefaciens SQR9, on crop yield and leaf microbiota were investigated. The results showed that leaves sprayed with amino acid liquid fertilizer (AA) and liquid biological fertilizer (AA9) persistently increased cowpea yields compared to the control amended with chemical fertilizer (CF). Fertilization with amino acid fertilizer showed no significant difference in microbial composition compared with the CF treatment; however, the introduction of functional microbes altered the microbial composition. Pearson correlation analysis, VPA analysis and SEM models all revealed that the amino acids liquid fertilizer application, but not the functional strain or the altered microbiota, performed as the direct driver attributing to yield enhancement. We conclude that leaf fertilization with a novel amino acid liquid fertilizer can greatly enhance the crop yield and that the addition of beneficial microbes may perform the role in further altering the composition of leaf microbiota.

Low-Dose Radiation Promotes the Proliferation and Migration of AGE-Treated Endothelial Progenitor Cells Derived from Bone Marrow via Activating SDF-1/CXCR4/ERK Signaling Pathway.

Low-dose radiation (LDR) has been confirmed to mobilize bone marrow-derived endothelial progenitor cells (EPCs) and promote diabetic wound healing. But it is unclear whether LDR acts directly on EPCs and promotes their proliferation and migration. Given the key role of advanced glycosylation end products (AGE) in the pathogenesis of diabetes, we used AGE to induce EPC damage. We then investigated the effect of LDR on the proliferation and migration of AGE-treated EPCs and explored the underlying mechanisms. EPCs cultured in vitro were treated with different concentrations of AGE, and the cells were then exposed to different low doses and treated with a specific antagonist for CXCR4, AMD3100 (1 lmol/l). The proliferation and migration abilities of EPCs were detected using the CCK-8 and wound healing assays, respectively. The mRNA and protein expression of SDF-1 and CXCR4 in AGE-treated EPCs were measured using qPCR and Western blot analysis, respectively. The expressions of ERK and phosphorylated ERK (pERK) were detected using Western blot analysis. The results showed that 200 mg/l and 400 mg/l AGE had an inhibitory effect on the proliferation of EPCs, and this inhibitory effect was exerted in a dose- and time-dependent manner. AGE significantly reduced the migration ability of EPCs cultured in vitro. After the cells received either 50 or 75 mGy low-dose irradiation, the proliferation of EPCs and AGE-treated EPCs was clearly increased; in addition, LDR also enhanced cell migration ability, but this enhancement was counteracted by AMD3100. Results from qPCR and Western blot analysis showed that LDR increased the mRNA and protein expression of SDF-1/ CXCR4. LDR also upregulated pERK expression in EPCs and AGE-treated EPCs, but LDR-induced upregulation of pERK expression was inhibited by AMD3100. These findings indicate that LDR can directly activate the SDF-1/CXCR4 biological axis and downstream ERK signaling pathway, and promote the proliferation and migration abilities of EPCs by increasing the expression of SDF-1, CXCR4 and pERK in EPCs.