Genomic analyses of metal resistance genes in three plant growth promoting bacteria of legume plants in Northwest mine tailings, China

To better understand the diversity of metal resistance genetic determinant from microbes that survived at metal tailings in northwest of China, a highly elevated level of heavy metal containing region, genomic analyses was conducted using genome sequence of three native metal-resistant plant growth promoting bacteria（PGPB）. It shows that： Mesorhizobium amorphae CCNWGS0123 contains metal transporters from P-type ATPase, CDF（Cation Diffusion Facilitator）, Hup E/Ure J and CHR（chromate ion transporter） family involved in copper, zinc, nickel as well as chromate resistance and homeostasis. Meanwhile, the putative Cop A/Cue O system is expected to mediate copper resistance in Sinorhizobium meliloti CCNWSX0020 while Znt A transporter, assisted with putative Czc D, determines zinc tolerance in Agrobacterium tumefaciens CCNWGS0286. The greenhouse experiment provides the consistent evidence of the plant growth promoting effects of these microbes on their hosts by nitrogen fixation and/or indoleacetic acid（IAA） secretion,indicating a potential in-site phytoremediation usage in the mining tailing regions of China.

Legume Green Manuring Improves Soil Fertility and Plant Growth of Eucalyptus Plantation in South Subtropical China

Legume green manure is extensively planted to improve soil fertility in crop field.However,the application of legume in Eucalyptus plantation is still limited and depends on site specific and species.Therefore,the objective of this study was to determine the effects of green manure interplantation on soil fertility and plant growth of Eucalyptus plantation in a short term.A field experiment of one year was established to investigate the green manure growth,forest soil nutrients and Eucalyptus plant growth inter-planted with two legume species(Tephrosia candida,TC and Sesbania cannabina,SC)at south subtropical China.Legumes were inter-planted in linear among the tree space of Eucalyptus stand.Result showed that the green manure inter-plantation increased soil organic matter by 9.66%of TC and 18.44%of SC.Soil available nitrogen,phosphorus and potassium were improved significantly by the legume treatments as well.The increment of height and diameter at breast height of Eucalyptus during the experiment was significant in legume treatments.Thus,the timber volume increment was improved significantly by 46.81%of TC and 35.47%of SC compared with the control treatment.Therefore,the inter-plantation of legume green manure under the Eucalyptus plantation is effective to improve soil fertility and tree growth.Such a measure is potential and referenced for the sustainable forest management.

Differentiation trajectories and biofunctions of symbiotic and un-symbiotic fate cells in root nodules of Medicago truncatula

The root nodule is a complex symbiotic nitrogen fixation factory,in which cells are highly heterogeneous.However,the differentiation trajectories and interconnection of nodule cells remain largely unknown.In this study,we set up a modified protocol for nodule protoplast preparation and performed a single-cell RNA sequencing profiling of the indeterminate Medicago truncatula nodule.We designated 13 cell clusters with specific expression patterns in 14-day post inoculation nodules and constructed a spatial and functional cellular map based on experimental data and bioinformatic analyses.Pseudotime analysis further revealed that two groups of apical meristematic cells develop into symbiotic and un-symbiotic fate cells along their particular trajectories.Biofunction analysis of each cell cluster revealed their particularity and interrelation,especially that the un-infected cells in nitrogen fixation zone are also involved in nitrogen assimilation by undertaking the asparagine synthesis.Collectively,our data offer an important resource for investigating the mechanism of nodule organogenesis and symbiotic nitrogen fixation.