Tobacco Root Microbial Community Composition Significantly Associated With Root-Knot Nematode Infections: Dynamic Changes in Microbiota and Growth Stage.

The root-knot nematode (RKN) is an important pathogen that affects the growth of many crops. Exploring the interaction of biocontrol bacteria-pathogens-host root microbes is the theoretical basis for improving colonization and controlling the effect of biocontrol bacteria in the rhizosphere. Therefore, 16S and 18S rRNA sequencing technology was used to explore the microbial composition and diversity of tobacco roots (rhizosphere and endophytic) at different growth stages in typical tobacco RKN-infected areas for 2 consecutive years. We observed that RKN infection changed the α-diversity and microbial composition of root microorganisms and drove the transformation of microorganisms from bacteria to fungi. The abundance of Sphingomonas decreased significantly from 18% to less than 3%, while the abundance of Rhizobiaceae increased from 4 to 15% at the early growth stage during the first planting year, and it promoted the proliferation of Chryseobacterium at the late growth stage in rhizosphere microorganisms with the highest abundance of 17%. The overall trend of rhizosphere microorganisms changed in the early growth stage with increasing growth time. The specific results were as follows: (1) Rhizobiaceae and Chryseobacterium increased rapidly after 75 days, became the main abundant bacteria in the rhizosphere microorganisms. (2) The dominant flora in fungi were Fusarium and Setophoma. (3) Comparing the root microbes in 2017 and 2018, RKN infection significantly promoted the proliferation of Pseudomonas and Setophoma in both the rhizosphere and endophytes during the second year of continuous tobacco planting, increasing the relative abundance of Pseudomonas from 2 to 25%. Pseudomonas was determined to play an important role in plant pest control. Finally, a total of 32 strains of growth-promoting bacteria were screened from tobacco rhizosphere bacteria infected with RKN through a combination of 16S rRNA sequencing and life-promoting tests. The results of this research are helpful for analyzing the relationship between RKNs and bacteria in plants, providing reference data for elucidating the pathogenesis of RKNs and new ideas for the biological control of RKNs. GRAPHICAL ABSTRACT.

Potassium accumulation characteristics and expression of related genes involved in potassium metabolism in a high-potassium variety: tobacco (Nicotiana tabacum) as a model.

We investigated potassium (K) accumulation characteristics and expression of K metabolism related genes in one high-K variety (ND202) and a common variety (NC89) of tobacco (Nicotiana tabacum L.). Results showed that K accumulation and leaf K content in ND202 were higher than those in NC89. The distribution rate and K accumulation in the leaves of ND202 increased significantly, while the distribution rate in the roots and stems had lower values. In addition, the maximum K accumulation rate and high-speed K accumulation duration in ND202 were found to be better than those in NC89. The expression of NKT1 in the upper and middle leaves of ND202 had an advantage, and the relative expression of NtKC1 and NtTPK1 in both the upper and middle leaves, as well as the roots, was also significantly upregulated. Conversely, the expression of NTRK1 in the lower leaves and roots of ND202 was weaker. ND202 had significantly greater expression levels of NtHAK1 than NC89 in the upper and middle leaves and roots; moreover, the expression of NtKT12 in the upper leaves and roots of ND202 was also higher. In comparison with common varieties, high-K varieties had a stronger ability to absorb and accumulate K. They also possessed higher expression of K+ channel- and transporter-related genes and showed a superior K accumulation rate and longer duration of high-speed K accumulation. Furthermore, K accumulation rate at 40-60days can be suggested as an important reference for the selection of high-K tobacco varieties.

Activation of potassium released from soil by root-secreted organic acids in different varieties of tobacco (Nicotiana tabacum).

Organic acids secreted from the roots of plants play important roles in nutrient acquisition and metal detoxification; however, the precise underlying mechanisms of these processes remain poorly understood. In the present study we examined the content of organic acids exuded from roots and the effects of these organic acids on the activation of slowly available potassium (K) at different K levels, including normal K supply and K-deficient conditions. In addition, the study system also comprised a high-K tobacco variety (ND202) and two common ones (K326 and NC89). Our results showed that high-K varieties exhibited significantly higher contents of organic acids in its root exudates and available K in both rhizosphere and non-rhizosphere soils than the other varieties. This research also suggested that a cyclic process in which soil was acidified after being complexed by organic acids was involved in the release of slowly available K, and that this process primarily depended on the soil pH at high organic acids concentrations, but the complexation of organic ligands became dominant at low concentrations. In conclusion, tobacco roots secrete organic acids to increase available K content and improve the utilisation rate of soil K. High-K varieties probably enhance slowly available K activation by secreting relatively high amounts of organic acids, thus leading to more available K in soil for absorption by plants.

Renal mucinous tubular and spindle cell carcinoma combined with multiple bone metastasis: a case report and literature review / 北京大学学报(医学版)

Mucinous tubular and spindle cell carcinoma (MTSCC) is a rare sub-type of renal cell carcinoma (RCC). It has been considered to be a kind of "indolent" tumor with low-grade fashion, weak invasive capacity and relatively favorable prognosis. However, in the current case, a 3.7 cm×2.8 cm spherical mass with contrast enhancement was found in the left kidney incidentally by computed tomography (CT) in a 60-year-old male patient. A lesion in the right humerus (2.1 cm×1.6 cm×3.1 cm) was found at the same time without any symptoms or sign of pathological fracture by magnetic resonance (MR) imaging. Further positron emission tomography (PET)/CT scan which was ordered immediately after admission suggested multiple bone destruction including skull, pelvis, sternum, right humerus and femur, left scapula, multiple vertebrae and libs. Pathological examination after radical nephrectomy and palliative resection with internal fixation of the lesion in the right humerus indicated that both renal (3.0 cm×3.0 cm×2.5 cm) and bone lesions were MTSCC with the features of high-grade ovoid epithelioid cells, cord-like spindle cells and mucinous matrix under light microscope. The diagnosis of renal MTSCC concurrent with multiple bone metastasis was made. This case report suggested the necessity of general evaluation, especially bone scan for possible distant metastasis, as MTSCC might present unexpected advanced behaviors without any orthopedic symptoms. The behavior of bone metastasis might be associated with male and elderly age. MTSCC has similar enhancement features to papillary RCC on CT scan. As results, attentions are needed to differentiate MTSCC from papillary RCC as they both tend to show lesser enhancement degrees than cortex. Rather than exhibiting a dedifferentiating appearance, the pathological characteristics of bone metastasis lesion were close to those of primary renal lesion. The reason of distant metastasis to the bone remained unclear, negative expression of cytokeratin (CK) 7 might be attributed to. Though immunotherapy, chemotherapy and target therapy could all be methods for systematic therapies, procedures to remove renal lesions and prevent skeletal related events are still highly recommended.