Dynamic root microbiome sustains soybean productivity under unbalanced fertilization.

Root-associated microbiomes contribute to plant growth and health, and are dynamically affected by plant development and changes in the soil environment. However, how different fertilizer regimes affect quantitative changes in microbial assembly to effect plant growth remains obscure. Here, we explore the temporal dynamics of the root-associated bacteria of soybean using quantitative microbiome profiling (QMP) to examine its response to unbalanced fertilizer treatments (i.e., lacking either N, P or K) and its role in sustaining plant growth after four decades of unbalanced fertilization. We show that the root-associated bacteria exhibit strong succession during plant development, and bacterial loads largely increase at later stages, particularly for Bacteroidetes. Unbalanced fertilization has a significant effect on the assembly of the soybean rhizosphere bacteria, and in the absence of N fertilizer the bacterial community diverges from that of fertilized plants, while lacking P fertilizer impedes the total load and turnover of rhizosphere bacteria. Importantly, a SynCom derived from the low-nitrogen-enriched cluster is capable of stimulating plant growth, corresponding with the stabilized soybean productivity in the absence of N fertilizer. These findings provide new insights in the quantitative dynamics of the root-associated microbiome and highlight a key ecological cluster with prospects for sustainable agricultural management.

Effects of PLAB on apoptosis and Smad signal pathway of hypertrophic scar fibroblasts.

Pseudolaric acid-B (PLAB), a diterpene acid, was isolated from the root and trunk barks of Pseudolarix kaempferi. It has shown antifungal and anti-fertility effects and cytotoxic activities in previous studies. Our goals are to study the effects of PLAB on cell proliferation and Smad signal pathway of hypertrophic scar fibroblasts. Our results showed that PLAB induced apoptosis in hypertrophic scar fibroblasts and inhibited cell proliferation of hypertrophic scar fibroblast. MTT assay showed that its IC(50) value toward hypertrophic scar fibroblasts was 12.9+/-1.20 micromol/L. Furthermore, the results of cell growth curve matched with the above results. Inducing apoptosis by PLAB in hypertrophic scar fibroblast was assessed by various morphological and biochemical characteristics, including cell shrinkage, chromatin condensation, membrane blebbing, formation of apoptotic bodies, and DNA ladder formation. A typical "Sub-G1 peak" was also checked through flow cytometry. The Smad2 and Smad7 mRNA levels of 48-h PLAB treatment were determined by reverse transcription-polymerase chain reaction (RT-PCR) 48 h later. RT-PCR showed that Smad7 mRNA level increased and significant differences were observed between control group and experimental group (P<0.05); While there is no significant difference in Smad2 mRNA between the two groups. Our results showed that PLAB interfered with the microtubule dynamics of tubulin polymerisation and depolymerisation, which results in the inhibition of chromosomal segregation in mitosis and consequently the inhibition of cell division. These results suggest that PLAB inhibits hypertrophic scar fibroblast growth through apoptosis and Smad signal pathway.