CgNis1's Impact on Virulence and Stress Response in Colletotrichum gloeosporioides.

Pepper anthracnose caused by Colletotrichum gloeosporioides infection is an important fungal disease and represents a serious threat to pepper yield and quality. At present, the pathogenic molecular mechanism of C. gloeosporioides is not very clear. In our study, we characterized the function of C. gloeosporioides CgNis1, a homolog of Magnaporthe oryzae MoNis1. We found that the ∆Cgnis1 mutant reduced the growth rate and was defective in conidiation. Although the rate of appressorium formation was unaffected, the germ tube was found to be abnormal. CgNis1 was shown to be involved in the H2O2 stress response and maintaining cell membrane permeability. The pathogenicity assays performed in this study indicated that the deletion of CgNIS1 is associated with virulence. Our results indicate that CgNis1 is necessary for the growth, development, and pathogenicity of the fungus. This work provides an in-depth analysis of the Nis1 protein, helps to enhance studies on pathogen-related molecular mechanisms, and provides a theoretical basis for the prevention and control of C. gloeosporioides in peppers.

Protein kinase A regulatory subunit is required for normal growth, zoosporogenesis, and pathogenicity in Phytophthora sojae.

Phytophthora sojae, one of the most devastating Oomycete pathogens, causes severe diseases that lead to economic loss in the soybean industry. The production of zoospores play a crucial role during the development of Phytophthora disease. In this work, CRISPR/Cas9 genome editing technology were used to obtain protein kinase A regulatory subunit (PsPkaR) knockout mutants. The role of PsPkaR in the production of zoospores and pathogenicity of P. sojae was analyzed. The overall findings indicate that PsPkaR is involved in regulating the growth process of P. sojae, primarily affecting the hyphal morphology and growth rate. Additionally, PsPkaR participates in the regulation of the release process of zoospores. Specifically, knocking-out PsPkaR resulted in incomplete cytoplasmic differentiation and uneven protoplast division, leading to abnormal release of zoospores. Furthermore, when the PsPkaR knockout mutants were inoculated on soybean leaves, the pathogenicity was significantly reduced compared to that of the wild-type and control strains. These findings of this study provide important clues and evidence regarding the role of the cAMP-PKA signaling pathway in the interaction between P. sojae and its host. This work contributes to a better understanding of the pathogenic mechanism of P. sojae and the development of corresponding prevention and control strategies.

Residue behavior and processing factors of thirteen field-applied pesticides during the production of Chinese traditional fermented chopped pepper and chili powder.

In this study, the fate, processing factors and relationship with physicochemical properties of thirteen pesticides in field-collected pepper samples during Chinese chopped pepper and chili powder production was systematically studied. The washing, air-drying, chopping and salting and fermentation processes reduced 24.8%-62.8%, 0.9%-26.4%, 25.1%-50.3% and 16.3%-90.0% of thirteen pesticide residues, respectively, while the sun-drying processing increased the residues of eleven pesticides by 1.27-5.19 fold. The PFs of thirteen pesticides were < 1 in chopped pepper production and the PFs of eleven pesticides were more than 1 for chili powder production. The chopped pepper processing efficiency have most negative correlation with octanol-water partition coefficient. In contrast, the chili powder processing efficiency have most positive correlation with vapour pressure. Thus, this study can offer important references for assessment the pesticide residue levels in Chinese traditional fermented chopped pepper and chili powder production from fresh peppers.

Appressoria Formation in Phytopathogenic Fungi Suppressed by Antimicrobial Peptides and Hybrid Peptides from Black Soldier Flies.

Antimicrobial peptides (AMPs) from black solider flies (Hermetia illucens, BSF) exhibiting broad-spectrum antimicrobial activity are the most promising green substitutes for preventing the infection of phytopathogenic fungi; therefore, AMPs have been a focal topic of research. Recently, many studies have focused on the antibacterial activities of BSF AMPs against animal pathogens; however, currently, their antifungal activities against phytopathogenic fungi remain unclear. In this study, 7 AMPs selected from 34 predicted AMPs based on BSF metagenomics were artificially synthesized. When conidia from the hemibiotrophic phytopathogenic fungi Magnaporthe oryzae and Colletotrichum acutatum were treated with the selected AMPs, three selected AMPs-CAD1, CAD5, and CAD7-showed high appressorium formation inhibited by lengthened germ tubes. Additionally, the MIC50 concentrations of the inhibited appressorium formations were 40 µM, 43 µM, and 43 µM for M. oryzae, while 51 µM, 49 µM, and 44 µM were observed for C. acutatum, respectively. A tandem hybrid AMP named CAD-Con comprising CAD1, CAD5, and CAD7 significantly enhanced antifungal activities, and the MIC50 concentrations against M. oryzae and C. acutatum were 15 µM and 22 µM, respectively. In comparison with the wild type, they were both significantly reduced in terms of virulence when infection assays were performed using the treated conidia of M. oryzae or C. acutatum by CAD1, CAD5, CAD7, or CAD-Con. Meanwhile, their expression levels of CAD1, CAD5, and CAD7 could also be activated and significantly increased after the BSF larvae were treated with the conidia of M. oryzae or C. acutatum, respectively. To our knowledge, the antifungal activities of BSF AMPs against plant pathogenic fungi, which help us to seek potential AMPs with antifungal activities, provide proof of the effectiveness of green control strategies for crop production.

Co-infection of TYLCV and ToCV increases cathepsin B and promotes ToCV transmission by Bemisia tabaci MED.

Tomato disease is an important disease affecting agricultural production, and the combined infection of tomato chlorosis virus (ToCV) and tomato yellow leaf curl virus (TYLCV) has gradually expanded in recent years, but no effective control method has been developed to date. Both viruses are transmitted by Bemisia tabaci Mediteranean (MED). Previously, we found that after B. tabaci MED was fed on ToCV-and TYLCV-infected plants, the transmission efficiency of ToCV was significantly higher than that on plants infected only with ToCV. Therefore, we hypothesize that co-infection could enhance the transmission rates of the virus. In this study, transcriptome sequencing was performed to compare the changes of related transcription factors in B. tabaci MED co-infected with ToCV and TYLCV and infected only with ToCV. Hence, transmission experiments were carried out using B. tabaci MED to clarify the role of cathepsin in virus transmission. The gene expression level and enzyme activity of cathepsin B (Cath B) in B. tabaci MED co-infected with ToCV and TYLCV increased compared with those under ToCV infection alone. After the decrease in cathepsin activity in B. tabaci MED or cathepsin B was silenced, its ability to acquire and transmit ToCV was significantly reduced. We verified the hypothesis that the relative expression of cathepsin B was reduced, which helped reduce ToCV transmission by B. tabaci MED. Therefore, it was speculated that cathepsin has profound research significance in the control of B. tabaci MED and the spread of viral diseases.

Overexpression of ATP Synthase Subunit Beta (Atp2) Confers Enhanced Blast Disease Resistance in Transgenic Rice.

Previous research has shown that the pathogenicity and appressorium development of Magnaporthe oryzae can be inhibited by the ATP synthase subunit beta (Atp2) present in the photosynthetic bacterium Rhodopseudomonas palustris. In the present study, transgenic plants overexpressing the ATP2 gene were generated via genetic transformation in the Zhonghua11 (ZH11) genetic background. We compared the blast resistance and immune response of ATP2-overexpressing lines and wild-type plants. The expression of the Atp2 protein and the physiology, biochemistry, and growth traits of the mutant plants were also examined. The results showed that, compared with the wild-type plant ZH11, transgenic rice plants heterologously expressing ATP2 had no significant defects in agronomic traits, but the disease lesions caused by the rice blast fungus were significantly reduced. When infected by the rice blast fungus, the transgenic rice plants exhibited stronger antioxidant enzyme activity and a greater ratio of chlorophyll a to chlorophyll b. Furthermore, the immune response was triggered stronger in transgenic rice, especially the increase in reactive oxygen species (ROS), was more strongly triggered in plants. In summary, the expression of ATP2 as an antifungal protein in rice could improve the ability of rice to resist rice blast.

Novel Plant Growth Regulator Guvermectin from Plant Growth-Promoting Rhizobacteria Boosts Biomass and Grain Yield in Rice.

Food is a fundamental human right, and global food security is threatened by crop production. Plant growth regulators (PGRs) play an essential role in improving crop yield and quality, and this study reports on a novel PGR, termed guvermectin (GV), isolated from plant growth-promoting rhizobacteria, which can promote root and coleoptile growth, tillering, and early maturing in rice. GV is a nucleoside analogue like cytokinin (CK), but it was found that GV significantly promoted root and hypocotyl growth, which is different from the function of CK in Arabidopsis. The Arabidopsis CK receptor triple mutant ahk2-2 ahk3-3 cre1-12 still showed a GV response. Moreover, GV led different growth-promoting traits from auxin, gibberellin (GA), and brassinosteroid (BR) in Arabidopsis and rice. The results from a four-year field trial involving 28 rice varieties showed that seed-soaking treatment with GV increased the yields by 6.2 to 19.6%, outperforming the 4.0 to 10.8% for CK, 1.6 to 16.9% for BR, and 2.2 to 7.1% for GA-auxin-BR mixture. Transcriptome analysis demonstrated that GV induced different transcriptome patterns from CK, auxin, BR, and GA, and SAUR genes may regulate GV-mediated plant growth and development. This study suggests that GV represents a novel PGR with a unique signal perception and transduction pathway in plants.

Effects of dazomet combined with Rhodopsesudomonas palustris PSB-06 on root-knot nematode, Meloidogyne incognita infecting ginger and soil microorganisms diversity.

Root-knot nematode, Meloidogyne incognita is one of the most important nematodes affecting ginger crop. Rhodopseudomonas palustris PSB-06, as effective microbial fertilizer in increasing plant growth and suppressing soil-borne disease of many crops has been reported. The combination of R. palustris PSB-06 and dazomet treatments had been proved to inhibit root-knot nematode on ginger and increase ginger yield in our preliminary study. The field experiments were conducted to elucidate the reasons behind this finding, and followed by next-generation sequencing to determine the microbial population structures in ginger root rhizosphere. The results showed that combination of R. palustris PSB-06 and dazomet treatment had a synergetic effect by achieving of 80.00% reduction in root-knot nematode numbers less than soil without treatment, and also could increase 37.37% of ginger yield through increasing the contents of chlorophyll and total protein in ginger leaves. Microbiota composition and alpha diversity varied with treatments and growth stages, soil bacterial diversity rapidly increased after planting ginger. In addition, the combined treatment could increase diversity and community composition of probiotic bacteria, and decrease those of soil-borne pathogenic fungi comparing to the soil treated with dazomet alone. Meanwhile, it could also effectively increase soil organic matter, available phosphorus and available potassium. Analysis of correlation between soil microorganisms and physicochemical properties indicated that the soil pH value and available phosphorus content were important factors that could affect soil microorganisms structure at the harvest stage. The bacterial family was more closely correlated with the soil physicochemical properties than the fungal family. Therefore, the combination of R. palustris PSB-06 and dazomet was considered as an effective method to control root-knot nematode disease and improve ginger soil conditions.

Proteomics Analysis Reveals the Molecular Mechanism of MoPer1 Regulating the Development and Pathogenicity of Magnaporthe oryzae.

Glycosylphosphatidylinositol (GPI) anchoring the protein GPI modification post-transcriptionally is commonly seen. In our previous study, MoPer1, a GPI anchoring essential factor, has a critical effect on Magnaporthe oryzae growth, pathogenicity, and conidiogenesis, but its molecular mechanism is not clear. Here, we extracted the glycoproteins from the ΔMoper1 mutant and wild-type Guy11 to analyze their differential levels by quantitative proteomic analysis of TMT markers. After background subtraction, a total of 431 proteins, with significant changes in expression, were successfully identified, and these differential proteins were involved in biological regulation, as well as cellular process and metabolic process, binding, catalytic activity, and other aspects. Moreover, we found that MoPer1 regulates the expression of 14 proteins involved in growth, development, and pathogenicity of M. oryzae. The above findings shed light on MoPer1's underlying mechanism in regulating growth, development, and pathogenicity of M. oryzae.

The nonstructural protein NSs encoded by tomato zonate spot virus suppresses RNA silencing by interacting with NbSGS3.

Viral suppressors of RNA silencing (VSRs) are encoded by diverse viruses to counteract the RNA silencing-mediated defence mounted by the virus-infected host cells. In this study, we identified the NSs protein encoded by tomato zonate spot virus (TZSV) as a potent VSR, and used a potato virus X (PVX)-based heterologous expression system to demonstrate TZSV NSs as a viral pathogenicity factor that intensified PVX symptoms in Nicotiana benthamiana. We then used a yeast two-hybrid screen to identify the suppressor of gene silencing 3 protein of N. benthamiana (NbSGS3), a known component of the plant RNA silencing pathway, as an interaction partner of TZSV NSs. We verified this interaction in plant cells with bimolecular fluorescence complementation, subcellular colocalization, and co-immunoprecipitation. We further revealed that the NSs-NbSGS3 interaction correlated with the VSR activity of TZSV NSs. TZSV NSs reduced the concentration of NbSGS3 protein in plant cells, probably through the ubiquitination and autophagy pathways. Interestingly, TZSV infection, but not NSs overexpression, significantly up-regulated the NbSGS3 transcript levels. Our data indicate that TZSV NSs suppresses RNA silencing of the host plant and enhances TZSV pathogenicity through its interaction with NbSGS3. This study reveals a novel molecular mechanism of NSs-mediated suppression of plant host antiviral defence.

Association Mapping and Functional Analysis of Rice Cold Tolerance QTLs at the Bud Burst Stage.

Cold tolerance at the bud burst stage (CTB) is a key trait for direct-seeded rice. Although quantitative trait loci (QTL) affecting CTB in rice have been mapped using traditional linkage mapping and genome-wide association study (GWAS) methods, the underlying genes remain unknown. In this study, we evaluated the CTB phenotype of 339 cultivars in the Rice Diversity Panel II (RDP II) collection. GWAS identified four QTLs associated with CTB (qCTBs), distributed on chromosomes 1-3. Among them, qCTB-1-1 overlaps with Osa-miR319b, a known cold tolerance micro RNA gene. The other three qCTBs have not been reported. In addition, we characterised the candidate gene OsRab11C1 for qCTB-1-2 that encodes a Rab protein belonging to the small GTP-binding protein family. Overexpression of OsRab11C1 significantly reduced CTB, while gene knockout elevated CTB as well as cold tolerance at the seedling stage, suggesting that OsRab11C1 negatively regulates rice cold tolerance. Molecular analysis revealed that OsRab11C1 modulates cold tolerance by suppressing the abscisic acid signalling pathway and proline biosynthesis. Using RDP II and GWAS, we identified four qCTBs that are involved in CTB and determined the function of the candidate gene OsRab11C1 in cold tolerance. Our results demonstrate that OsRab11C1 is a negative regulator of cold tolerance and knocking out of the gene by genome-editing may provide enhanced cold tolerance in rice.

Integrated Analysis of microRNA and mRNA Transcriptome Reveals the Molecular Mechanism of Solanum lycopersicum Response to Bemisia tabaci and Tomato chlorosis virus.

Tomato chlorosis virus (ToCV), is one of the most devastating cultivated tomato viruses, seriously threatened the growth of crops worldwide. As the vector of ToCV, the whitefly Bemisia tabaci Mediterranean (MED) is mainly responsible for the rapid spread of ToCV. The current understanding of tomato plant responses to this virus and B. tabaci is very limited. To understand the molecular mechanism of the interaction between tomato, ToCV and B. tabaci, we adopted a next-generation sequencing approach to decipher miRNAs and mRNAs that are differentially expressed under the infection of B. tabaci and ToCV in tomato plants. Our data revealed that 6199 mRNAs were significantly regulated, and the differentially expressed genes were most significantly associated with the plant-pathogen interaction, the MAPK signaling pathway, the glyoxylate, and the carbon fixation in photosynthetic organisms and photosynthesis related proteins. Concomitantly, 242 differentially expressed miRNAs were detected, including novel putative miRNAs. Sly-miR159, sly-miR9471b-3p, and sly-miR162 were the most expressed miRNAs in each sample compare to control group. Moreover, we compared the similarities and differences of gene expression in tomato plant caused by infection or co-infection of B. tabaci and ToCV. Taken together, the analysis reported in this article lays a solid foundation for further research on the interaction between tomato, ToCV and B. tabaci, and provide evidence for the identification of potential key genes that influences virus transmission in tomato plants.

GroEL protein from the potential biocontrol agent Rhodopseudomonas palustris enhances resistance to rice blast disease.

BACKGROUND: GroEL, which is a chaperone, plays a key role in maintaining protein homeostasis and, among other functions, serves to prevent protein misfolding and aggregation. In addition, the GroEL protein also has a significant effect on enhancing plant resistance and inhibiting plant diseases. However, the function of the GroEL protein in the inhibition of rice blast remains unknown. RESULTS: Field experiment results show that photosynthetic bacteria PSB-06 have a good control effect on Magnaporthe oryzae. PSB-06 also can promote rice growth and enhance stress resistance. A GroEL protein which was separated and purified from photosynthetic bacteria had a significant antagonistic effect on appressorial formation and pathogenicity of Magnaporthe oryzae, meanwhile transcriptional analysis demonstrated that the GroEL protein could improve the expression of defense gene of rice. CONCLUSION: Our results show that the photosynthetic bacteria Rhodopseudomonas palustris significantly controls rice blast disease. Its action involves an extracellular GroEL protein, which inhibits appressoria formation, antagonizes the pathogenicity of Magnaporthe oryzae and promotes a host defense response. The research results provide evidence of the potential of this photosynthetic bacterium as a biocontrol agent at least for rice blast control. © 2021 Society of Chemical Industry.

Exploration of Intrinsic Microbial Community Modulators in the Rice Endosphere Indicates a Key Role of Distinct Bacterial Taxa Across Different Cultivars.

Microbial communities associated with the plant phyllosphere and endosphere can have both beneficial as well as detrimental effects on their hosts. There is an ongoing debate to which extend the phyllosphere and endosphere microbiome assembly is controlled by the host plant how pronounced cultivar effects are. We investigated the bacterial and fungal communities from the phyllosphere and endosphere of 10 different rice cultivars grown under identical environmental conditions in the frame of a targeted approach to identify drivers of community assembly. The results indicated that the endophytic bacterial communities were clearly separated into two groups. The α-diversity and microbial network complexity within Group I were significantly lower than in Group II. Moreover, the genera Nocardioides, Microvirga, and Gaiella were significantly more abundant in Group II and only present in the interaction networks of this group. These three genera were significantly correlated with α- and ß-diversity of the endophytic bacterial community and thus identified as major drivers of the endosphere community. We have identified keystone taxa that shape endophytic bacterial communities of different rice cultivars. Our overall findings provide new insights into plant-microbe interactions, and may contribute to targeted improvements of rice varieties in the future.

Aphid endosymbiont facilitates virus transmission by modulating the volatile profile of host plants.

BACKGROUND: Most plant viruses rely on vectors for their transmission and spread. One of the outstanding biological questions concerning the vector-pathogen-symbiont multi-trophic interactions is the potential involvement of vector symbionts in the virus transmission process. Here, we used a multi-factorial system containing a non-persistent plant virus, cucumber mosaic virus (CMV), its primary vector, green peach aphid, Myzus persicae, and the obligate endosymbiont, Buchnera aphidicola to explore this uncharted territory. RESULTS: Based on our preliminary research, we hypothesized that aphid endosymbiont B. aphidicola can facilitate CMV transmission by modulating plant volatile profiles. Gene expression analyses demonstrated that CMV infection reduced B. aphidicola abundance in M. persicae, in which lower abundance of B. aphidicola was associated with a preference shift in aphids from infected to healthy plants. Volatile profile analyses confirmed that feeding by aphids with lower B. aphidicola titers reduced the production of attractants, while increased the emission of deterrents. As a result, M. persicae changed their feeding preference from infected to healthy plants. CONCLUSIONS: We conclude that CMV infection reduces the B. aphidicola abundance in M. persicae. When viruliferous aphids feed on host plants, dynamic changes in obligate symbionts lead to a shift in plant volatiles from attraction to avoidance, thereby switching insect vector's feeding preference from infected to healthy plants.

Tomato Chlorosis Virus Infection Facilitates Bemisia tabaci MED Reproduction by Elevating Vitellogenin Expression.

Transmission of plant pathogenic viruses mostly relies on insect vectors. Plant virus could enhance its transmission by modulating the vector. Previously, we showed that feeding on virus infected plants can promote the reproduction of the sweet potato whitefly, Bemisia tabaci MED (Q biotype). In this study, using a whitefly-Tomato chlorosis virus (ToCV)-tomato system, we investigated how ToCV modulates B. tabaci MED reproduction to facilitate its spread. Here, we hypothesized that ToCV-infected tomato plants would increase B. tabaci MED fecundity via elevated vitellogenin (Vg) gene expression. As a result, fecundity and the relative expression of B. tabaci MED Vg was measured on ToCV-infected and uninfected tomato plants on days 4, 8, 12, 16, 20 and 24. The role of Vg on B. tabaci MED reproduction was examined in the presence and absence of ToCV using dietary RNAi. ToCV infection significantly increased B. tabaci MED fecundity on days 12, 16 and 20, and elevated Vg expression on days 8, 12 and 16. Both ovarian development and fecundity of B. tabaci MED were suppressed when Vg was silenced with or without ToCV infection. These combined results suggest that ToCV infection increases B. tabaci MED fecundity via elevated Vg expression.

Genome Sequence Resource for Colletotrichum scovillei, the Cause of Anthracnose Disease of Chili.

Colletotrichum species cause anthracnose disease on the economically important spice crop chili. A total of 24 Colletotrichum species are known to infect chili and cause anthracnose. C. scovillei belongs to the C. acutatum species complex, and it shows greater aggressiveness than other species, particularly in the case of inoculation onto the nonwounded fruits of chili plants. The current work introduces an initial Illumina-Nanopore hybrid draft genome for C. scovillei TJNH1 together with the related annotations. Knowledge of this genome sequence provides an important reference genome of C. scovillei and will help further understand the pathogenic mechanism of C. scovillei to plant.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The high-affinity phosphodiesterase PcPdeH is involved in the polarized growth and pathogenicity of Phytophthora capsici.

The cAMP signaling pathway has been shown to be important in controlling morphological changes and pathogenicity in plant pathogens. In the present study, we identified PcPdeH, a gene encoding a high-affinity phosphodiesterase (PDE), which is a key regulator of the cAMP signaling pathway. To elucidate the function of PcPdeH, PcPdeH-knockout mutants were obtained using a type II CRISPR/Cas9 system in Phytophthora capsici. The knockout transformants of PcPdeH showed vegetative growth defects and abnormal cyst germination. Infection assays indicated that compared with the wild type, PcPdeH-knockout mutants showed significantly reduced virulence on pepper and tobacco leaves and exhibited increased (1.5-2-fold) cAMP levels relative to the wild-type and CK strains. Based on these phenotypic features, we propose that PcPdeH is crucial for vegetative growth, cyst germination and pathogenicity in P. capsici.

The effects of Rhodopseudomonas palustris PSB06 and CGA009 with different agricultural applications on rice growth and rhizosphere bacterial communities.

In recent years, the photosynthetic bacteria have been used widely in agriculture, but the effects of different agricultural applications on crop rhizosphere microorganism and crops are lack. In this study, we provide new insights into the structure and composition of the rice root-associated microbiomes as well as the effect on crop of the Rhodopseudomonas palustris(R. palustris) PSB06 and CGA009 at the rice seedling stage with seed immersion and root irrigation. Compare with CK group, the length of stem, the peroxidase (POD), and superoxide dismutase (SOD) activities in PSB06 treatment group was significantly higher, while the length of stem in CGA009 treatment group was significantly higher. The POD and SOD activities in CGA009 treatment groups only were higher slightly than the CK group. In the study, the dominant phyla were Proteobacteria (51.95-61.66%), Bacteroidetes (5.40-9.39%), Acidobacteria (4.50-10.52%), Actinobacteria (5.06-8.14%), Planctomycetes (2.90-4.48%), Chloroflexi (2.23-5.06%) and Firmicutes (2.38-7.30%), accounted for 87% bacterial sequences. The principal coordinate analysis (pCoA) and mantel results showed the two application actions of R. palustris CGA009 and PSB06 had significant effects on rice rhizosphere bacterial communities (p < 0.05). The PSB06 can significantly promote the rice growth and enhance stress resistance of rice at the seedling stage, while the R. palustris CGA009 has no significant effect on rice. Dissimilarity test and canonical correspondence analysis (CCA) results showed that the TN and pH were the key factors affecting rice rhizosphere bacterial community in the seedling stage. This study will provide some guidance advices for the study of the microecological regulation of photosynthetic bacteria on crops.

Characterization of Rhodopseudomonas palustris population dynamics on tobacco phyllosphere and induction of plant resistance to Tobacco mosaic virus.

Although many biocontrol bacteria can be used to improve plant tolerance to stresses and to promote plant growth, the hostile environmental conditions on plant phyllosphere and the limited knowledge on bacterial colonization on plant phyllosphere minimized the beneficial effects produced by the biocontrol bacteria. Rhodopseudomonas palustris strain GJ-22 is known as a phyllosphere biocontrol agent. In this paper, we described detailed processes of strain GJ-22 colony establishment at various colonization stages. Four different types of bacterial colonies, Type 1, scattered single cells; Type 2, small cell clusters; Type 3, small cell aggregates; and Type 4, large cell aggregates, were observed in the course of bacterial colonization. We categorized bacterial colonization into four phases, which were, Phase I: bacterial colony exists as Type 1 and cell population reduced quickly; Phase II: Type 1 evolved into Type 2 and cell population remained steady; Phase III: Type 3 arose and replaced Type 2, and cell population expanded slowly; and Phase IV: Type 3 matured into Type 4 and cell population increased quickly. We have shown that the preferable location sites of bacterial aggregates on leaf phyllosphere are grooves between plant epidermal cells. Analyses of expressions of plant defence-related genes showed that, starting from Phase III, bacterial cells in the Type 3 and Type 4 colonies produced unidentified signals to induce host defence against Tobacco mosaic virus infection. In addition, we determined the crucial role of aggregates formation of GJ-22 cell on plant phyllosphere in terms of bacterial cell stress tolerance and ISR (induced systemic resistance) priming. To our knowledge, this is the first report focused on the colonization process of a phyllosphere biocontrol agent and gave a clear description on the morphological shift of bacterial colony on phyllosphere.