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/lp/springer-journals/the-influences-on-conidiophore-pleomorphism-inclonostachys-rosea-and-K2f0rQ86uL
- Publisher
- Springer Journals
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- Copyright © 2009 by University of Milan and Springer
- Subject
- Life Sciences; Microbiology; Microbial Genetics and Genomics; Microbial Ecology; Fungus Genetics; Medical Microbiology; Applied Microbiology
- ISSN
- 1590-4261
- eISSN
- 1869-2044
- DOI
- 10.1007/BF03175596
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Abstract
Annals of Microbiology, 59 (1) 39-44 (2009) The influences on conidiophore pleomorphism in Clonostachys rosea and RAPD analysis to the mutant producing only verticillate conidiophores Xiaowei HUANG, Yunxia LI, Yingzhen SU, Junmei DING, Keqin ZHANG* Laboratory for Conservation and Utilization of Bio-Resources, and Key Laboratory for Microbial Resources of the Ministry of Education, Yunnan University, Kunming, Yunnan, 650091, China Received 14 October 2008 / Accepted 22 January 2009 Abstract - Being an effective biocontrol agent, Clonostachys rosea possess morphologically two different kinds of conidiophore structures, verticillate and penicillate respectively. However, the factors that influenced this morphological pleomorphism and its related genetic background remains to be elucidated. In this study, single-spore isolates were obtained from these two types of conidiophores and observed for their cultural and morphological characteristics. The stability of pleomorphism was confirmed through three-months of continuous inoculation and incubation. Additionally, the influences on conidiophore’s morphology under different cultural conditions were also recorded. Our data indicated that the fungal inhibitor thiabendazole changed the formation of conidiophores with only verticillate type produced, which subsequently had effects on its abilities to infect the plant pathogenic fungus Rhizoctonia solani and nematodes Panagrellus redivivus in our bioassay. However, the genomic analysis by Random Amplified Polymorphic DNA (RAPD) assay showed no obvious differences detected in the mutant with only verticillate conidiophores and its parent strain, suggesting the change in conidiophore’s type should be attributed to different transcriptional patterns. Key words: Clonostachys rosea; conidiophore pleomorphism; RAPD analysis. INTRODUCTION more than two different growth types, such as Hirsutella pichilinguensis parasitizing the larva of Lepidoptera; it Pleomorphism generally refers to the phenomenon that a has been described as having not only conidiophores fungus contains both the sexual and asexual reproductive that are transparent, smooth, thin-walled, pouroveal or structures at the same time and that it produces more than obpyriformis, but also conidiophores with big, narrow-rod one kind of spores. In the narrow sense, it refers to having phragmospore with thick wall diaphragm, at the same two or more types of asexual reproductive structures time; (3) conidiophores having a variety of sporonts, (Liang and Roland, 1998). Carmichael (1981) classified the for example, it has been reported that entomogenous asexual pleomorphism into three categories and included fungi Paecilomyces farinosus, Paecilomyces tenuipes and a large number of examples. Gams (1982) summarized Hirsutella stibelliformis could all produce conidiophores Carmichael’s points using more data and reclassified it into that were peduncle and gleba in coremium and mycelium two categories. Recent elaboration on the investigation of at the same time. In another species, Paecilomyces fungal pleomorphism demonstrated that there were other odonatae, there are two types of conidiophores, with pleomorphisms of the chlamydospore, fungus nuclear and the conidiophore of Acremonium first, followed by the the hypha besides the spore asexuality pleomorphism production of penicillate conidiophores (Liu et al., 2000). (Liang, 1997). Among them, conidiophore pleomorphism in The fungus Paecilomyces militaris generates verticillate fungi is currently considered as belonging to the following and penicillate conidiophores successively (Liang and three categories: (1) conidiophores containing more than Roland, 1998). two types of conidia with dissimilar appearances grow on Clonostachys rosea, an important biocontrol agent the same strain; examples of this group include Fusarium against pathogenic fungi as well as nematodes, has also sp. that has both big spores and small ones at the same been described as having an asexual pleomorphism (Hoopen time (Pitt and Hocking, 1997); (2) conidiophores that have et al., 2003; Dong et al., 2004). Its conidiophores contain the morphological characters of Verticillium sp., Penicillium sp. and Trichothecium sp., and this pleomorphism had contributed to the confusion in anamorph nomenclature * Corresponding Author. Phone: 86-871-5034878; Fax: 86-871-5034838; E-mail: kqzhang111@yahoo.com.cn and taxonomy. Often, such polymorphic conidiophores 40 X. HUANG et al. may also be mistakenly identified as contaminants of other 114 mg/L, polyoxin 210 mg/L, and then cultivated at 28 °C for fungal species. Today, despite the solution on taxonomic ten days. status, the conditions influencing conidiophore types All experiments above were performed with at least 3 and its related genetic background are still unclear. In repeats. this study, the stability of pleomorphism was confirmed by studying single-spore isolates. In addition, several The bioassay of Clonostachys rosea. The bioassay against potential factors that could affect the generation of nematodes was performed according to the method reported by conidiophores were also investigated. Furthermore, we Liu and Chen (2000). The tested strains of C. rosea (including compared the genetic background in the mutant with only wild strain and the mutant) were inoculated to the centre of the verticillate conidiophores to its parent strain. PDA plates and cultivated at 25 °C for 7 days, while the same cul- ture media without C. rosea were employed as the control. After washing the nematode Panagrellus redivivus thoroughly with MATERIALS AND METHODS a 10 mM sterilized PBS (phosphate buffered saline, pH 7.0), a suspension containing 500 nematodes (about 100 μl) was added Strains and media. The fungus Clonostachys rosea 176 in the culture media. The culture plate was exposed to sterilized was isolated from the larvae of nematodes in Jianshui air for half an hour to vaporize the redundant water. Then the County, Yunnan Province, and deposited in the Laboratory culture plates were incubated for 48 h. The nematodes were then for Conservation and Utilization of Bio-resources, Yunnan washed with 5 ml of 0.1% Tween-20, and about 200 nematodes University. were selected randomly and observed under the microscope. The The media used in the experiments were Corn Meal agar numbers of dead and living nematodes were counted, and the (CMA), Potato Dextrose agar (PDA) (Yu et al., 2007) and percentage of dead was calculated: Basic medium. The ingredients of Basic medium include (%, w/v): 1 maltose, 0.2 NaNO , 0.05 MgSO ·7H O, 0.05 Fixation percentage = [the number of dead nematodes - the total 3 4 2 KH PO , 0.065 Na HPO , 0.05 KCl, 2 agar, pH 6.5. number of the nematodes x (1 - the mortality of control)] / (the 2 4 2 4 total number of the nematodes) x 100 Isolation of single spores and morphological observation. The isolation of single spores was performed In the experiment to test parasitic activity of C. rosea against based on the modified method previously used (Li et al., Rhizoctonia solani, both of them were co-cultured on 1% PDA at 2006b). Briefly, when C. rosea grew with diameter of 1-2 28 °C, with about 2 cm of overlap between the two colonies. The cm on PDA medium, samples were examined using a parasitic capacity was determined based on the relative numbers dissecting microscope. Single spore was isolated with a of sclerotia formed by R. solani. The number of the sclerotia sterilized toothpick and then cultivated on fresh PDA again produced by R. solani in the overlapped colony and the number at 28 °C. This process would be repeated for at least three of the sclerotia formed in the absence of C. rosea at the opposite months. Morphological properties of the conidiophores were end on the same media were counted, taking into account the observed by using light microscopy (BH 2; Olympus). size of the area where sclerotia was counted. The latter treat- ment was used as the negative control. Influence of different cultural conditions on conidiophores formation and the growth in The parasitic capacity = (the sclerotia formed in the control - the Clonostachys rosea. The effect of pH was assayed by sclerotia formed in the overlapped section) / (the sclerotia of the cultivating the fungus on PDA at pH 2.0, 2.5, 3.0, 3.5, control) x 100 4.0, 4.5, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, and 14.0. The fungus was inoculated on the culture media Based on the percentage of sclerotia reduction, relative para- using an inoculumn of 5 mm in diameter. After ten days sitism were classified to five grades 0, 1, 2, 3, 4 corresponding of incubation at 28 °C, the fungus was observed both to the percent of sclerotial reduction in the overlapped colony by microscopically and macroscopically. 0-25%, 25-50%, 50-75%, 75-100% respectively. The effect of temperature was assayed by cultivating the These bioassay experiments above were repeated at least fungus on PDA at 10, 15, 20, 25, 28, 30, 33, 35, and 37 °C for ten times. ten days. To test the effect of light, C. rosea was cultivated in poor or Genomic DNA extraction. DNA extraction was performed by good light conditions, respectively on PDA at 28 °C for ten days. CTAB method. Briefly, 200 mg fungus mycelium was ground To test the effect of the carbon source, 1, 2, 3 and 4% (w/v) to a fine paste in approximately 500 μl of CTAB buffer. CTAB/ glucose, sucrose, glycerol was added to the Basic medium to fungi extract mixture was added to a microfuge tube, and then substitute the original source of carbon individually. The fungus incubate for about 15 min at 55 °C in a water bath. After that, was cultivated at 28 °C for ten days and then observed under centrifuge was performed at 12000 x g for 5 min to remove cell microscope. debris. The supernatant would be transfer to clean tubes fol- To investigate the influence of nitrogen source on C. rosea, lowed by adding 250 μl of chloroform:iso amyl alcohol (24:1) to 0.2, 0.5 and 1% (w/v) NaNO , aspartic acid, peptone and each tube. After mixing by inversion, the mixture was spun at (NH) SO were added to the Basic medium individually, and then 13000 rpm for 10 min, and then the upper aqueous phase only 2 4 cultivated at 28 °C for ten days. (contains the DNA) was transfer to new tubes. By adding 50 μl of Additionally, the effects on the formation of conidiophores 7.5 M ammonium acetate and 1 ml of ice cold 100% ethanol, the were also assayed by adding different fungal inhibitors: thiaben- genomic DNA was precipitated at 13000 rpm for 30 min. Twice dazole (TBZ) 0.13 ml/L, dimethachlon 0.25 ml/L, pingyangmycin wash to DNA was performed using 500 μl of ice cold 75% etha- 0.25 ml/L, carbendazim 45 mg/L, kasugamycin 0.9 mg/L, thiran nol. At last, the pellet of DNA would be dried and resuspended in 60 mg/L, tricyclazole 45 mg/L, tricyclazole 60 mg/L, hymexazol 50 μl sterile DNase free water. Ann. Microbiol., 59 (1), 39-44 (2009) 41 TABLE 1 - The primers used in RAPD analysis Primer No. Sequences of Primer No. Sequences of primer (5’-3’) primer (5’-3’) OPA-02 TGCCGAGCTG S-22 TGCCGAGCTG OPC-15 GGAACTGCTT S-23 AGTCAGCCAC OPD-05 TGAGCGGACA S-28 GTGACGTAGG OPL-02 TGGGCGTCAA S-36 AGTCAGCCAC OPE-20 AACGGTGACC S-51 AGCGCCATTG OPN-14 TCGTGCGGGT RAPD analysis. The RAPD reaction was performed in a total produce two types of conidiophores. In detail, the elementary volume of 50 μl consisting of 5 μl template DNA, 10X PCR buffer, (verticillate) conidia could be observed after two days of incuba- 3.5 mM MgCl2, 200 μM deoxynucleoside triphosphates, 1.25 U of tion on PDA at 25 °C followed by penicillate conidiophores from Taq DNA polymerase (Fermentas, Lithuania), and 1 μM of primer. the fourth day. When 5 microscopic fields were randomly selected PCR cycling procedures were as follows; 45 cycles of 94 °C for 1 to every single spore isolate and both conidiophores were min, 37 °C for 1 min and 72 °C for 1 min. A final step of exten- counted, our results showed that the single spore isolates from sion was applied at 72 °C for 10 min. After PCR reaction, 5 μl penicillate conidiophores would generate 83.6 ± 7.1 verticillate products were analyzed by electrophoresis in a 1.5% agarose gel type and 337.0 ± 23.2 penicillate type respectively; while the with TBE (tris-borate-EDTA) buffer. single spore isolates from verticillate conidiophores would gener- Eleven random primers (Table 1) were used to determine the ate 92.7 ± 11.3 verticillate type conidiophores and 330.0 ± 24.6 genetic differences between the mutant and its parent strain. penicillate type respectively. The statistical analysis revealed that Besides that, two additional wild isolates from some other origins all the strains from different single spore isolates had the similar were employed in our RAPD analysis as controls. percentages of two types of conidiophores (Fig. 1). Statistical analysis. All data from repetitive experiments were The influence on the morphology of conidiophores in expressed as mean ± SE. The results were analyzed using Clonostachys rosea SPSS13.0. Significant differences among experimental time In all of the factors we tested, only TBZ, a kind of fungal inhibitor, points were analyzed within a level using a one-way ANOVA. could significantly influence the production of conidiophores’ types in Differences were considered to be statistically significant at the C. rosea. Medium containing TBZ produced a mutant with only verti- level of p < 0.05. cillate conidiophores when the concentration of TBZ was 0.13 ml/L. Furthermore, the microscopic observation illustrated that those verticillate conidiophores in the mutant had no obvious difference in RESULTS the morphologic characters compared with the wild strain (Fig. 2B). It was also revealed in our data that this phenotype generating one Stability of conidiophores pleomorphism in type of conidiophores would keep stable in the several successive Clonostachys rosea inoculations if this mutant continued to grow on medium with the Asexual single spore isolates were continuously inoculated and same TBZ concentration. But when this mutant was transferred to cultivated for three-months. It was found that each isolate the normal medium and then the repeated inoculations (3-5) went whether from verticillate or penicillate conidiophores would stably on, it would at last revert to generate both types of conidiophores. FIG. 1 - Comparison of the formation of penicillate and verticil- FIG. 2 - Growth of the mutant strain producing only penicil- late conidiophores between P and V group. P group: late conidiophores on PDA medium containing fungal single spore isolates from penicillate conidiophores; inhibitor thiabendazole TBZ (A), and the microscopic V group: single spore isolates from verticillate conidi- observation to verticillate conidiophores of the wild ophores; PC: represent the formation of penicillate strain and the mutant strain (B). conidiophores; VC: represent the formation of verticil- late conidiophores. Number of strains tested (n = 9). Error bars represent +SE. 42 X. HUANG et al. Meanwhile, our experimental data indicated that medium pH, growth temperature, illumination, as well as our tested carbon or nitrogen sources primarily affect the growth of mycelium and the numbers of conidia in C. rosea, but not the formation of conidi- ophores pleomorphism. When the pH of the culture medium was adjusted to ≥ 3.0, C. rosea produced both verticillate and peni- cillate conidiophores, with different pH within this range showing variable effects on the growth rate of C. rosea. When the pH of the culture medium was between 4.5-11.0, this fungus grew nor- mally and the growth reached the maximum when pH was 6.0. After incubation for ten days on the media of pH 11.0-14.0, the fungus displayed light snuffcoloured with yellow drips at the cen- tre of colonies. No obvious growth of C. rosea could be observed on the culture medium of pH < 3.0. Clonostachys rosea grew well at temperatures between 20 and 34 °C, and the optimum growth temperature was 28 °C. At lower temperatures or the temperature exceeded 35 °C, the aerial mycelium was loose with fewer conidiophores and mostly the verticillate type. Illuminations could also FIG. 3 - The agar electrophoresis of PCR products in our RAPD influence the pigment of spores but with relatively little analysis. Lanes 2 and 3 represent the parent strain and effect on conidiophores pleomorphism as well as the its mutant; lanes 1 and 4 represent the other two wild growth rate of C. rosea. All examined carbon or nitrogen strains with different origins. Lane M represent the DNA sources supported the growth of C. rosea with two types of marker, including 2000, 1600, 1000, 750, 500, 250 and conidiophores, and they only show an effect on the growth 100 bp. OPE-20, S-36, OPN-14, S-22, S-23, OPD-05, of hypha. In the sugar concentration gradient experiment, OPA-02, S-28, OPC-15, S-51 and OPC-02 represent the the greatest hyphal growth rate was observed when the random primers used in our analysis, respectively. sugar concentration was 4% glucose. Among all of the tested nitrogen sources, NaNO was comparatively fit for the growth of C. rosea while sparse mycelium could be that there were no obviously different profiles found in all of the found when the nitrogen source became (NH ) SO . PCR products between the mutant and its parent strain, suggest- 4 2 4 ing that they have no detected differences in genome. Contrarily, Comparisons of the parasitic capacity of the the other two wild strains with different origins had significantly Clonostachys rosea mutant and wild type strains distinct profiles at the genomic level compared to the mutant as against nematodes Panagrellus redivivus and well as its parent strain. phytopathogenic fungus Rhizoctonia solani To understand if the phenotype of conidiophore pleomorphism has effects on the abilities to biocontrol nematodes or phy- DISCUSSION topathogenic fungi, we compare the infection efficacies of the mutant and wild strains against P. redivivus and R. solani. In Fungi not only have pleomorphism of sexuality, but also have our bioassay against P. redivivus, we counted the nematode pleomorphism in asexual structures. The same fungus can mortalities after 48 h treatment. It was shown that in the mutant have several anamorphic names because of pleomorphism producing only the verticillate conidiophores, the infection capac- of their asexual structures (Henrebert, 1971). As a result, ity to nematodes was much weaker (47.1% ± 5.4) than that of the classification and identification of such fungi can be wild strain with two types of conidiophores (74.6% ± 8.9; p < problematic. Mycologists have made several proposals 0.05). However, PDA culture medium without C. rosea, as the to solve the taxonomic problem, but a unified solution negative controls, had less than 10% of nematocidal activities remained elusive. Clonostachys rosea has different kinds of for the same time. asexual conidiophores characteristic of those in the genera Our bioassay against R. solani revealed that the wild strain Verticillium, Penicillium, and Trichothecium. In addition, its of C. rosea could significantly inhibit the sclerotia formation by colony morphology and conidiophore structure can change R. solani (p < 0.05). On the overlapped colonies, most mycilia dramatically among cultural conditions. Therefore, it is of R. solani were parasitized by the C. rosea. Our statistic data necessary to observe the morphologic characteristics of showed 57.9% ± 10.2 parasitic capacity, corresponding to the different types of conidiophores and the potential changes Parasitism grade 3. To the mutant strain producing only verticil- of colony morphology under different culture conditions. late conidiophores, the parasitic capacity decreased to 38.6% ± Meanwhile, obtaining the mutants with only one type of 7.4ˈ corresponding to the parasitism grade 2. conidiophores can also supply an alternative for comparing their genetic background, and further understand the Genetic analysis to the mutant and its parent strain molecular mechanisms of formation of conidiophores by RAPD plemorphism. In order to know if there are any genetic differences between the Our study revealed that most of the common growth mutant and its parent strain of C. rosea, RAPD typing was used in conditions, including pHs, temperatures, illuminations and our study. The mutant strain producing only verticillate conidio- the nutrition in culture medium, only showed variable phores and three strains were all successfully typed using eleven effects on hyphal growth rates on C. rosea except that primers in RAPD method, and the examples of the electrophoretic the fungal inhibitor TBZ could change the formation of profiles were shown in Fig. 3, respectively. Data analysis showed conidiophores’ type. Clonostachys rosea on medium with Ann. Microbiol., 59 (1), 39-44 (2009) 43 a proper concentration of TBZ produced only verticillate Acknowledgement conidiophores and this phenotype could be kept stable This work was supported by projects from the Department on TBZ cultural medium. However, when the mutant of Science and Technology of Yunnan Province, P. R. China mycelia were transferred to normal media without any (No. 2006PY01-27, 2006C0006Q, 2007C0007Z). TBZ, two types of conidiophores gradually re-appeared after repeated inoculation. 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Journal
Annals of Microbiology – Springer Journals
Published: Nov 24, 2009