Isolation and characterization of phosphate-solubilizing bacterium Pantoea rhizosphaerae sp. nov. from Acer truncatum rhizosphere soil and its effect on Acer truncatum growth.

The Acer truncatum Bunge, widely distributed in North China, shows excellent tolerance to low-P soils. However, little information is available on potential phosphate-solubilizing bacterial (PSB) strains from the A. truncatum rhizosphere. The objectives of this work were to isolate and characterize PSB from A. truncatum rhizosphere soil and to evaluate the effect of inoculation with the selected strain on A. truncatum seedlings. The strains were characterized on the basis of phenotypic characteristics, carbon source utilization pattern, fatty acid methyl esters analysis, 16S rRNA gene and the whole-genome sequence. A Gram-negative and rod-shaped bacterium, designated MQR6T, showed a high capacity to solubilize phosphate and produce indole-3-acetic acid (IAA) and siderophores. The strain can solubilize tricalcium phosphate (TCP) and rock phosphate (RP), and the solubilization of TCP was about 60% more effective than RP. Phylogenetic analyses based on the 16S rRNA gene and whole-genome sequences revealed that strain MQR6T formed a distinct phyletic lineage as a new species within the genus Pantoea. The digital DNA-DNA hybridization value between strain MQR6T and the closely related strains was 19.5-23.3%. The major cellular fatty acids were summed feature 3 (C16:1ω7c and/or C16:1ω6c), summed feature 8 (C18:1ω6c and/or C18:1ω7c), C14:0, C16:0, and C17:0 cyclo. Several genes related to IAA production, phosphonate transport, phosphate solubilization and siderophore biogenesis were found in the MQR6T genome. Furthermore, inoculation with the strain MQR6T significantly improved plant height, trunk diameter, dry weight and P accumulation in roots and shoot of A. truncatum seedlings compared to non-inoculated control. These plant parameters were improved even further in the treatment with both inoculation and P fertilization. Our results suggested that MQR6T represented a new species we named Pantoea rhizosphaerae, as a plant growth-promoting rhizobacterium that can solubilize inorganic P and improve growth of A. truncatum seedlings, emerging as a potential strategy to improve A. truncatum cultivation.

Study on a new type of environment-friendly polymer and its preliminary application as soil consolidation agent during tree transplanting.

Transplanting trees with rhizospheric soil is an important way to facilitate tree survival in the process of landscaping and reforestation. Traditional way to prevent looseness of rhizospheric soil is forming soil balls around the roots with bags, boxes or rope wrapping, which is cumbersome, laborious and easy to break. This study is aimed to develop a new type of degradable environment-friendly polymer as soil consolidation agent to facilitate tree transplanting. In this paper, the KGM/CA/PVA ternary blending soil consolidation agent was prepared by using Konjac glucomannan (KGM), chitosan (CA) and polyvinyl alcohol (PVA) as raw materials. Through the verification and evaluation, the clay and sandy soil can be consolidated and formed into soil balls by the ternary blend adhesive, which was convenient for transportation. The preliminary application of the ternary blend adhesive in the transplanting process of sierra salvia, Japanese Spindle (Euonymus japonicus) and Juniperus sabina 'Tamaricifolia' confirmed that the application of soil consolidation agent can effectively solve the problem that the root ball of seedling is easily broken in the process of transplant. And the application of soil consolidation agent has no adverse effect on the growth of transplanted seedlings. The research and development of ternary blending soil consolidation agent and its preliminary application in seedling transplanting will provide a new solution to solve the problem of soil ball breakage in the process of seedling transplanting. This is an important stage in the development of new seedling transplanting technology. Therefore, the research and development of soil consolidation agent is of great significance.

First Report of Colletotrichum aenigma Causing Walnut Anthracnose in China.

English/Persian walnut (Juglans regia L.) is grown as an economically valuable crop in temperate and subtropical regions. In August of 2018, serious fruit anthracnose, with brown to black circular or subcircular or irregular sunken lesions (Fig.1A), occurred on walnut trees ("Xiangling" and "lvling") in 33 ha., 23 ha. and 20 ha. orchards in Lincheng and Neiqiu county, in Xingtai, Hebei, China. Diseased fruits were observed on 41% (19,000 trees), 31% (13,300 trees) and 34% (11,400 trees) walnut trees. Diseased leaves, with circular or irregular brown to gray sunken lesions, were observed on 2% (19,000 trees), 2% (13,300 trees) and 1% (11,400 trees) walnut trees. From each orchard, 25 diseased fruits and leaves were collected, respectively. Twenty-one single spore isolates were obtained from fruits of three orchards and none from leaves as described by Cai et al. (2009). Six representative isolates 1811-1, 1811-4, 1811-7, 1811-8, 1811-11 and 1811-18, two from each orchard, were selected for further study. Colonies on PDA grew 11.8 mm d-1 at 25℃ under a 12/12 h light/dark cycle for 7 d. The upper side of colonies was milky (Fig.1 B), and reverse side was dark brown to brownish yellow. A few acervuli were observed on colonies. Conidiogenous cells were cylindrical to clavate, 10.6-29.7 × 3.1-5.3 µm (mean=21.3 × 4.0 µm, n=30) (Fig.1F). Setae were not observed. Conidia were smooth-walled, aseptate, straight or slightly distorted, cylindrical with one end slightly acute or broadly rounded ends, and 16.6-21.6 × 6.0-7.5 µm (mean=19.2 × 6.7 µm, n=30) (Fig.1 C). Appressoria were mostly irregular in outline, deeply lobed or lightly lobed, gray brown to dark brown, 8.3-16.6 × 7.1-14.5 µm (mean=12.5 × 9.7 µm, n=30) (Fig.1 D-E). Microscopic features were similar to the description of C. aenigma (Weir et al. 2012). To further identify isolates, the ribosomal internal transcribed spacers (ITS), ß-tubulin 2 (TUB2), calmodulin (CAL), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), glutamine synthetase (GS) and chitin synthase (CHS-1) loci of representative isolates were amplified using ITS4/ITS5, Bt2a/Bt2b, CL1/CL2, GDF1/GDR1, GSF1/GSR1 and CHS-79F/CHS-345R primers (Prihastuti et al. 2009; Carbone & Kohn 1999). Sequences of representative isolate 1811-1 were submitted to GenBank (ITS: MN893316, TUB: MN893317, CAL: MN893312, GAPDH: MN893314, GS: MN893315, CHS-1: MN893313). Maximum likehood analysis of sequences of representative isolates and reference sequences of Colletotrichum spp. from GenBank revealed that six isolates clustered together with C. aenigma ex-type culture ICMP18608, and the bootstrap value was 100% (Fig.2). Pathogenicity tests were conducted on walnut fruit as described by Wang et al. (2017, 2018) and Cai et al. (2009). 10 wounded and 10 nonwounded fruits ("Xiangling", 35 mm diameter) were inoculated with isolates 1811-1, 1811-7 and 1811-11 conidial suspension (106 spore/mL) obtained from 10 d colonies grown on PDA at 25℃, respectively. 10 wounded and 10 nonwounded fruits were inoculated with sterile water. Inoculated and control fruits were incubated in containers at 25℃ in a 12/12 h light/dark cycle. After 10 days, necrotic lesions were observed in all inoculated fruits. The pathogen C. aenigma was reisolated from all inoculated fruits but not from control fruits. To our knowledge, this is the first report of C. aenigma causing walnut anthracnose in China. It is urgent to control walnut anthracnose caused by different species of Colletotrichum.

The Osmotin-Like Protein Gene PdOLP1 Is Involved in Secondary Cell Wall Biosynthesis during Wood Formation in Poplar.

Osmotin-like proteins (OLPs) mediate defenses against abiotic and biotic stresses and fungal pathogens in plants. However, no OLPs have been functionally elucidated in poplar. Here, we report an osmotin-like protein designated PdOLP1 from Populus deltoides (Marsh.). Expression analysis showed that PdOLP1 transcripts were mainly present in immature xylem and immature phloem during vascular tissue development in P. deltoides. We conducted phenotypic, anatomical, and molecular analyses of PdOLP1-overexpressing lines and the PdOLP1-downregulated hybrid poplar 84K (Populus alba × Populus glandulosa) (Hybrid poplar 84K PagOLP1, PagOLP2, PagOLP3 and PagOLP4 are highly homologous to PdOLP1, and are downregulated in PdOLP1-downregulated hybrid poplar 84K). The overexpression of PdOLP1 led to a reduction in the radial width and cell layer number in the xylem and phloem zones, in expression of genes involved in lignin biosynthesis, and in the fibers and vessels of xylem cell walls in the overexpressing lines. Additionally, the xylem vessels and fibers of PdOLP1-downregulated poplar exhibited increased secondary cell wall thickness. Elevated expression of secondary wall biosynthetic genes was accompanied by increases in lignin content, dry weight biomass, and carbon storage in PdOLP1-downregulated lines. A PdOLP1 coexpression network was constructed and showed that PdOLP1 was coexpressed with a large number of genes involved in secondary cell wall biosynthesis and wood development in poplar. Moreover, based on transcriptional activation assays, PtobZIP5 and PtobHLH7 activated the PdOLP1 promoter, whereas PtoBLH8 and PtoWRKY40 repressed it. A yeast one-hybrid (Y1H) assay confirmed interaction of PtoBLH8, PtoMYB3, and PtoWRKY40 with the PdOLP1 promoter in vivo. Together, our results suggest that PdOLP1 is a negative regulator of secondary wall biosynthesis and may be valuable for manipulating secondary cell wall deposition to improve carbon fixation efficiency in tree species.

Genome-wide transcriptomic analysis of a desert willow, Salix psammophila, reveals the function of hub genes SpMDP1 and SpWRKY33 in drought tolerance.

BACKGROUND: Drought is a major environmental constraint to plant growth, development and productivity. Compared with most willows that are generally susceptible to drought, the desert willow Salix psammophila has extraordinary adaptation to drought stress. However, its molecular basis of drought tolerance is still largely unknown. RESULTS: During polyethylene glycol 6000 (PEG 6000)-simulated drought stress, we found that the osmotic adjustment substances were accumulated and the antioxidant enzyme activities were enhanced in S. psammophila roots. A total of 8172 differentially expressed genes were identified in roots of S. psammophila through RNA-Sequencing. Based on K-means clustering, their expression patterns were classified into nine clusters, which were enriched in several stress-related processes including transcriptional regulation, response to various stresses, cell death, etc. Moreover, 672 transcription factors from 45 gene families were differentially expressed under drought stress. Furthermore, a weighted gene co-expression network was constructed, and eight genes were identified as hub genes. We demonstrated the function of two hub genes, magnesium-dependent phosphatase 1 (SpMDP1) and SpWRKY33, through overexpression in Arabidopsis thaliana. Overexpression of the two hub genes enhanced the drought tolerance in transgenic plants, suggesting that the identification of candidate drought tolerance genes in this study was highly efficient and credible. CONCLUSIONS: Our study analyzed the physiological and molecular responses to drought stress in S. psammophila, and these results contribute to dissect the mechanism of drought tolerance of S. psammophila and facilitate identification of critical genes involved in drought tolerance for willow breeding.

Genome-Wide Characterization of the sHsp Gene Family in Salix suchowensis Reveals Its Functions under Different Abiotic Stresses.

Small heat shock proteins (sHsps) function mainly as molecular chaperones that play vital roles in response to diverse stresses, especially high temperature. However, little is known about the molecular characteristics and evolutionary history of the sHsp family in Salix suchowensis, an important bioenergy woody plant. In this study, 35 non-redundant sHsp genes were identified in S. suchowensis, and they were divided into four subfamilies (C, CP, PX, and MT) based on their phylogenetic relationships and predicted subcellular localization. Though the gene structure and conserved motif were relatively conserved, the sequences of the Hsp20 domain were diversified. Eight paralogous pairs were identified in the Ssu-sHsp family, in which five pairs were generated by tandem duplication events. Ka/Ks analysis indicated that Ssu-sHsps had undergone purifying selection. The expression profiles analysis showed Ssu-Hsps tissue-specific expression patterns, and they were induced by at least one abiotic stress. The expression correlation between two paralogous pairs (Ssu-sHsp22.2-CV/23.0-CV and 23.8-MT/25.6-MT) were less than 0.6, indicating that they were divergent during the evolution. Various cis-acting elements related to stress responses, hormone or development, were detected in the promoter of Ssu-sHsps. Furthermore, the co-expression network revealed the potential mechanism of Ssu-sHsps under stress tolerance and development. These results provide a foundation for further functional research on the Ssu-sHsp gene family in S. suchowensis.

[Biomass and yield of Betula platyphylla population in Mila Mount of Tibet].

Mila Mount in Southeast Tibet is the west boundary of the horizontal distribution of Betula platyphylla. It is also the highest altitude area in China and the world, where Betula platyphylla is distributed. Based on the investigation of regional sample plots and the analysis of analytic trees, this paper compared the biomass and yield of Betula platyphylla population at different slope orientation and different altitude. The results showed that the growth of Betula platyphylla was greatly interfered by human activities. The yearly productivity of Betula platyphylla grown in Mila Mount was 363.1-2,072.94 kg x hm(-2), and the biomass was 7,625.00-33,167.00 kg x hm(-2), indicating that the biomass of Betula platyphylla was quite different for different population. The productivity and biomass of Betula platyphylla coppice after cutting were lower than those of seedling forest, and there existed youth broken-down in the coppice. The zonal changes of water resources had no significant effect on the water allocation and the biomass of Betula platyphylla.

[Chemical properties of litter in dark coniferous forest of Sejila Mountains in Tibet].

The storage and chemical properties of the forest litter in dark coniferous forest of Sejila Mountain were studied. The results showed that the existing storage was 5.863 t.hm-2 and the annual litter fall was 0.3205 t.hm-2. It implied that the forest litter decomposed slowly and accumulated quickly, and the turnover of nutrient circles was slow. The contents of N, Ca, Na, and Mn nutrient elements in litter layer were in the order of un-decomposed layer (U layer) > semi-decomposed layer (S layer) > decomposed layer (D layer), those of K, Fe, and Mg were in the order of D layer > S layer > U layer, and P element content was in the order of U layer > D layer > S layer. The pool of elements was 78.483 kg.hm-2 N, 3.843 kg.hm-2 P, 48.205 kg.hm-2 K, 23.115 kg.hm-2 Ca, 13.157 kg.hm-2 Na, 30.554 kg.hm-2 Fe, 2.113 kg.hm-2 Mn and 27.513 kg.hm-2 Mg. The turnover of forest litter was the total of nutrient release accumulation. K, Fe, and Mg were enriched, and N, Ca, Na, Mn, and P were released with the turnover rate in the order of N > Ca > Na > Mn > P.