Soybean cyst nematode (SCN) is the most devastating pathogen of soybean. Our previous study showed that the plant growth-promoting rhizobacterium Bacillus simplex strain Sneb545 promotes soybean resistance to SCN. Here, we conducted a combined metabolomic and transcriptomic analysis to gain information regarding the biological mechanism of defence enhancement against SCN in Sneb545-treated soybean. To this end, we compared the transcriptome and metabolome of Sneb545-treated and non-treated soybeans under SCN infection. Transcriptomic analysis showed that 6792 gene transcripts were common in Sneb545-treated and non-treated soybeans. However, Sneb545-treated soybeans showed a higher concentration of various nematicidal metabolites, including 4-vinylphenol, methionine, piperine, and palmitic acid, than non-treated soybeans under SCN infection. Overall, our results validated and expanded the existing models regarding the co-regulation of gene expression and metabolites in plants, indicating the advantage of integrated system-oriented analysis.

Background: Root-knot nematode is one of the most significant diseases of vegetable crops in the world. Biological control with microbial antagonists has been emerged as a promising and eco-friendly treatment to control pathogens. The aim of this study was to screen and identify novel biocontrol agents against root-knot nematode, Meloidogyne incognita. Results: A total of 890 fungal isolates were obtained from rhizosphere soil of different crops and screened by nematicidal activity assays. Snef1910 strain showed high virulence against second stage juveniles (J2s) of M. incognita and identified as Trichoderma citrinoviride by morphology analysis and biomolecular assay. Furthermore, T. citrinoviride Snef1910 significantly inhibited egg hatching with the hatching inhibition percentages of 90.27, 77.50, and 67.06% at 48, 72, and 96 h after the treatment, respectively. The results of pot experiment showed that the metabolites of T. citrinoviride Snef1910 significantly decreased the number of root galls, J2s, and nematode egg masses and J2s population density in soil and significantly promoted the growth of tomato plants. In the field experiment, the biocontrol application showed that the control efficacy of T. citrinoviride Snef1910 against root-knot nematode was more than 50%. Meanwhile, T. citrinoviride Snef1910 increased the tomato plant biomass. Conclusions: T. citrinoviride strain Snef1910 could be used as a potential biological control agent against root-knot nematode, M. incognita.

Although pathogens such as nematodes are known to hijack nutrients from host plants, the mechanisms whereby nematodes obtain sugars from plants remain largely unknown. To determine the effects of nematode infection on host plant sugar allocation, soluble sugar (fructose, glucose, sucrose) content was investigated using high-performance liquid chromatography with refractive index detection and was found to increase significantly in tomato (Solanum lycopersicum, Sl) leaves and roots during early infection by root-knot nematodes (RKNs). To further analyze whether sugar transporters played a role in this process, the expression levels of sucrose transporter (SUT/SUC), Sugars Will Eventually be Exported Transporter (SWEET), tonoplast monosaccharide transporter (TMT), and vacuolar glucose transporter (VGT) gene family members were examined by qRT-PCR analysis after RKN infection. The results showed that three SlSUTs, 17 SlSWEETs, three SlTMTs, and SlVGT1 were upregulated in the leaves, whereas three SlSUTs, 17 SlSWEETs, two SlTMTs, and SlVGT1 were induced in the roots. To determine the function of the sugar transporters in the RKN infection process, we examined post-infection responses in the Atsuc2 mutant and pAtSUC2-GUS lines. β-glucuronidase expression was strongly induced at the infection sites, and RKN development was significantly arrested in the Atsuc2 mutant. Taken together, our analyses provide useful information for understanding the sugar transporter responses during early infection by RKNs in tomato.

Meloidogyne incognita and Meloidogyne graminicola are root-knot nematodes (RKNs) infecting rice (Oryza sativa L.) roots and severely decreasing yield, whose mechanisms of action remain unclear. We investigated RKN invasion and development in rice roots through RNA-seq transcriptome analysis. The results showed that 952 and 647 genes were differently expressed after 6 (invasion stage) and 18 (development stage) days post inoculation, respectively. Gene annotation showed that the differentially expressed genes were classified into diverse metabolic and stress response categories. Furthermore, phytohormone, transcription factor, redox signaling, and defense response pathways were enriched upon RKN infection. RNA-seq validation using qRT-PCR confirmed that CBL-interacting protein kinase (CIPK) genes (CIPK5, 8, 9, 11, 14, 23, 24, and 31) as well as brassinosteroid (BR)-related genes (OsBAK1, OsBRI1, D2, and D11) were altered by RKN infection. Analysis of the CIPK9 mutant and overexpressor indicated that the RKN populations were smaller in cipk9 and larger in CIPK9 OX, while more galls were produced in CIPK9 OX plant roots than the in wild-type roots. Significantly fewer numbers of second-stage infective juveniles (J2s) were observed in the plants expressing the BR biosynthesis gene D2 mutant and the BR receptor BRI1 activation-tagged mutant (bri1-D), and fewer galls were observed in bri1-D roots than in wild-type roots. The roots of plants expressing the regulator of ethylene signaling ERS1 (ethylene response sensor 1) mutant contained higher numbers of J2s and developed more galls compared with wild-type roots, suggesting that these signals function in RKN invasion or development. Our findings broaden our understanding of rice responses to RKN invasion and provide useful information for further research on RKN defense mechanisms.