B. subtilis CNBG-PGPR-1 induces methionine to regulate ethylene pathway and ROS scavenging for improving salt tolerance of tomato.

Soil salinity severely threatens plant growth and crop yields. The utilization of PGPR is an effective strategy for enhancing plant salt tolerance, but the mechanisms involved in this process have rarely been reported. In this study, we investigated the effects of Bacillus subtilis CNBG-PGPR-1 on improving plant salt tolerance and elucidated the molecular pathways involved. The results showed that CNBG-PGPR-1 significantly improved the cellular homeostasis and photosynthetic efficiency of leaves and reduced ion toxicity and osmotic stress caused by salt in tomato. Transcriptome analysis uncovered that CNBG-PGPR-1 enhanced plant salt tolerance through the activation of complex molecular pathways, with plant hormone signal transduction playing an important role. Comparative analysis and pharmacological experiments confirmed that the ethylene pathway was closely related to the beneficial effect of CNBG-PGPR-1 on improving plant salt tolerance. Furthermore, we found that methionine, a precursor of ethylene synthesis, significantly accumulated in response to CNBG-PGPR-1 in tomato. Exogenous L-methionine largely mimicked the beneficial effects of CNBG-PGPR-1 and activated the expression of ethylene pathway-related genes, indicating CNBG-PGPR-1 induces methionine accumulation to regulate the ethylene pathway in tomato. Finally, CNBG-PGPR-1 reduced salt-induced ROS by activating ROS scavenger-encoding genes, mainly involved in GSH metabolism and POD-related genes, which were also closely linked to methionine metabolism. Overall, our studies demonstrate that CNBG-PGPR-1-induced methionine is a key regulator in enhancing plant salt tolerance through the ethylene pathway and ROS scavenging, providing a novel understanding of the mechanism by which beneficial microbes improve plant salt tolerance.

First Report of Botrytis californica Causing Gray Mold on Blueberry in China.

Blueberry (Vaccinium corymbosum) is a perennial shrub which grows in acid soil. Its cultivation area has recently expanded rapidly due to its unique flavor and high nutritional value (Silver and Allen 2012). In June 2021, gray mold symptoms (8 to 12% incidence) were observed on harvested fruits of the blueberry cultivar 'Lanmei 1' during storage in Jiangning (31°50'N, 118°40'E), Nanjing, China. The infection started with wrinkles, atrophy, and depressed spots on the fruit surfaces, ultimately resulting in fruit rot. To determine the causal agent, diseased fruits were sampled and rinsed with sterile water (Gao et al. 2021). Small fragments (5 × 5 × 3 mm) of decayed tissues were excised and plated onto acidified potato dextrose agar (PDA) (containing 4 ml of 25% lactic acid per liter). Plates were incubated at 25°C for 3 to 5 days, and edges of fresh culture were transferred onto new plates. This procedure was repeated thrice to obtain pure cultures. Two isolates (BcB-1 and BcB-2) were obtained. Their colonies appeared whitish to gray, with an average daily growth rate of 11.3 ± 0.6 mm (no. of plates = 30). Conidiophores were long and erect, 2560.9 to 4885.3 µm × 10.7 to 13.0 µm in size. Conidia were one-celled, elliptical to ovoid, nearly hyaline, and 9.6 to 12.5 µm × 6.7 to 8.9 µm in size. Sclerotia were gray to black in color and round or irregular in shape. These morphological features were identical to those of Botrytis spp. (Amiri et al. 2018). To further identify the isolates, we amplified four genetic markers including internal transcribed spacer region (ITS), heat-shock protein 60 (HSP60), glyceraldehyde-3-phosphate dehydrogenase (G3PDH), and DNA-dependent RNA polymerase subunit II (RPBII) (Saito et al. 2014; Walker et al. 2011). Sequences of BcB-1 and BCB-2 were deposited in GenBank under accession nos. OP721062 and OP721063 for ITS, OP737384 and OP737385 for HSP60, OP746062 and OP746063 for G3PDH, and OP746064 and OP746065 for RPBII, respectively. BLAST analysis indicated that these sequences shared high identities (99 to 100%) with those of other B. californica isolates. Phylogenetic analysis showed that BcB-1 and BcB-2 clustered with several reference isolates in the B. californica clade. To confirm their pathogenicity, fresh blueberry fruits were surface sterilized with 0.5% sodium hypochlorite, rinsed with sterile water, air-dried, then wounded thrice per fruit using a sterile needle at the equator. Twenty wounded fruits were sprayed with 10 ml conidial suspension (1 × 105 conidia/ml) of each isolate onto the fruit surface. Twenty fruits treated with sterile water were used as controls. Inoculated or non-inoculated fruits were incubated at 25°C with 90% relative humidity. The pathogenicity test was performed twice. After 5 to 7 days, all inoculated fruits developed disease symptoms similar to those observed on the original fruits, while non-inoculated control fruits were asymptomatic. Re-isolated pathogens from the inoculated fruits exhibited identical morphological characteristics to those of BcB-1 and BcB-2. Their identity as B. californica was also verified based on their ITS sequences. Previously, B. californica has been reported to cause gray mold on blueberry in the Central Valley of California (Saito et al. 2016). To our knowledge, this is the first report of B. californica causing gray mold on post-harvest blueberry fruits in China. These results can provide the basis for future studies on the occurrence, prevention, and control of this disease.

Antifungal Activity and Possible Mechanism of Bacillus amyloliquefaciens FX2 Against the Postharvest Apple Ring Rot Pathogen.

Botryosphaeria dothidea-induced apple ring rot is one of the most serious postharvest diseases in apple production. In our preliminary work, we isolated a bacterial strain (FX2) from an infested apple orchard. Here, we confirmed the strong antifungal activity of FX2 on B. dothidea. Through phylogenetic analysis and morphological observations, we identified FX2 as a Bacillus amyloliquefaciens strain. We also found that 10% cell-free supernatant (CFS) of FX2 significantly affected mycelial growth and morphology and almost completely inhibited spore germination and germ tube elongation in B. dothidea. Furthermore, 10% CFS damaged the cell ultrastructure, resulting in a remarkable increase in cellular leakage in B. dothidea mycelia. Thus, CFS has the potential to effectively reduce in vivo B. dothidea infection, reduced lesion diameters to 64.7% compared with the control group, and reduced disease incidence by 15%. Finally, ultrafiltration, desalting chromatography, and anion exchange chromatography showed that the antifungal constituents in CFS are composed mainly of antifungal proteins. We further characterized these potential antifungal proteins via liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Herein, we provide novel insights into the antifungal mechanisms of B. amyloliquefaciens FX2, and we highlight its potential as a novel biocontrol agent for controlling postharvest apple ring rot.

Characterization and expression of the ABC family (G group) in 'Dangshansuli' pear (Pyrus bretschneideri Rehd.) and its russet mutant.

The plant genes encoding ABCGs that have been identified to date play a role in suberin formation in response to abiotic and biotic stress. In the present study, 80 ABCG genes were identified in 'Dangshansuli' Chinese white pear and designated as PbABCGs. Based on the structural characteristics and phylogenetic analysis, the PbABCG family genes could be classified into seven main groups: classes A-G. Segmental and dispersed duplications were the primary forces underlying the PbABCG gene family expansion in 'Dangshansuli' pear. Most of the PbABCG duplicated gene pairs date to the recent whole-genome duplication that occurred 30~45 million years ago. Purifying selection has also played a critical role in the evolution of the ABCG genes. Ten PbABCG genes screened in the transcriptome of 'Dangshansuli' pear and its russet mutant 'Xiusu' were validated, and the expression levels of the PbABCG genes exhibited significant differences at different stages. The results presented here will undoubtedly be useful for better understanding of the complexity of the PbABCG gene family and will facilitate the functional characterization of suberin formation in the russet mutant.

A plant growth-promoting bacteria Priestia megaterium JR48 induces plant resistance to the crucifer black rot via a salicylic acid-dependent signaling pathway.

Xanthomonas campestris pv. campestris (Xcc)-induced black rot is one of the most serious diseases in cruciferous plants. Using beneficial microbes to control this disease is promising. In our preliminary work, we isolated a bacterial strain (JR48) from a vegetable field. Here, we confirmed the plant-growth-promoting (PGP) effects of JR48 in planta, and identified JR48 as a Priestia megaterium strain. We found that JR48 was able to induce plant resistance to Xcc and prime plant defense responses including hydrogen peroxide (H2O2) accumulation and callose deposition with elevated expression of defense-related genes. Further, JR48 promoted lignin biosynthesis and raised accumulation of frees salicylic acid (SA) as well as expression of pathogenesis-related (PR) genes. Finally, we confirmed that JR48-induced plant resistance and defense responses requires SA signaling pathway. Together, our results revealed that JR48 promotes plant growth and induces plant resistance to the crucifer black rot probably through reinforcing SA accumulation and response, highlighting its potential as a novel biocontrol agent in the future.

Alloying effects on the microstructure and mechanical properties of nanocrystalline Ti-based alloyed thin films.

Ti-based films alloyed with various Ta or Zr contents were deposited on a Si (100) substrate by magnetron sputtering. Transmission electron microscopy observations suggested that the solute Ta and Zr atoms distributed uniformly in the matrix Ti, refining the grain size. The microstructure transformed from single phase α-Ti to the coexistence of (α + ß)-Ti when the Ta addition was increased to 18.2 at%. Hardness and strain rate sensitivity of the Ti-based alloyed films were evaluated by nanoindentation experiments, to show the effects of constituents and their contents. The hardness was found to change non-monotonously within the studied Ta or Zr range, which could be explained by alloying dependence of the strengthening mechanisms, including partial dislocation mechanism emanating from grain boundaries, solid solution strengthening, and solution pinning strengthening. Furthermore, a mechanistic model based on partial dislocation inhomogeneous nucleation was employed to describe the composition-dependent strain rate sensitivity of the alloyed Ti films.

The complete chloroplast genome sequence of Michelia compressa.

Michelia compressa is an evergreen ornamental tree species. The high-throughput sequencing technology was used to sequence and assemble the chloroplast genome of Michelia compressa. Results showed that the chloroplast genome is 160,061 bp in length, of which the inverted repeats sequence (IRs) is 26,581 bp, the large single-copy region (LSC) and the small single copy region (SSC) are 88,097 bp and 18,802 bp, respectively. The GC content of the plastome was 39.2%, with 43.2%, 37.9% and 34.2% in IRs, LSC and SSC, respectively. A total of 132 genes are annotated, 86 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. This study enriched the Michelia compressa genomic information which provides the basis for rational exploitation and utilization of germplasm resources.

Characterization and expression of the ABC family (G group) in 'Dangshansuli' pear (Pyrus bretschneideri Rehd.) and its russet mutant

Abstract The plant genes encoding ABCGs that have been identified to date play a role in suberin formation in response to abiotic and biotic stress. In the present study, 80 ABCG genes were identified in 'Dangshansuli' Chinese white pear and designated as PbABCGs. Based on the structural characteristics and phylogenetic analysis, the PbABCG family genes could be classified into seven main groups: classes A-G. Segmental and dispersed duplications were the primary forces underlying the PbABCG gene family expansion in 'Dangshansuli' pear. Most of the PbABCG duplicated gene pairs date to the recent whole-genome duplication that occurred 30~45 million years ago. Purifying selection has also played a critical role in the evolution of the ABCG genes. Ten PbABCG genes screened in the transcriptome of 'Dangshansuli' pear and its russet mutant 'Xiusu' were validated, and the expression levels of the PbABCG genes exhibited significant differences at different stages. The results presented here will undoubtedly be useful for better understanding of the complexity of the PbABCG gene family and will facilitate the functional characterization of suberin formation in the russet mutant.