Genes can be transferred horizontally between prokaryotes and eukaryotes in nature. The best-studied examples occur between Agrobacterium rhizogenes and certain Nicotiana spp. To investigate possible additional cases of horizontal gene transfer in nature between Agrobacterium and plants, a real-time polymerase chain reaction-based approach was employed to screen 127 plant species, belonging to 38 families of Dicotyledones, for the presence of oncogenes homologous to the transfer DNA fragments (T-DNA) from both A. tumefaciens and A. rhizogenes. Among all of the analyzed plant species, we found that only Linaria vulgaris contained sequences homologous to the T-DNA of A. rhizogenes. All screened L. vulgaris plants from various parts of Russia contained the same homologous sequences, including rolB, rolC, ORF13, ORF14, and mis genes. The same opine gene is found in the species of Nicotiana which contain genes of A. rhizogenes. In L. vulgaris, there are two copies of T-DNA organized as a single tandem imperfect direct repeat. The plant DNA sequence of the site of integration shows similarity to a retrotransposon. This site is most likely silent, suggesting that the T-DNA is not expressed. Attempts to demonstrate expression of the T-DNA genes were negative. Our study indicates that the frequency of gene transfer and fixation in the germline from Agrobacterium to plant hosts is rare in the natural environment.
ВВЕДЕНИЕВопросы эффективной идентификации видов растений, а также отслежи-вания их филогенетических отношений вызывали интерес на всем протяже-нии развития биологической науки. Возможность отличать представителей близких видов друг от друга может быть осложнена высоким полиморфизмом внутри каждого из видов, или напротив высоким межвидовым морфологичес-ким сходством (как в случае видов-двойников). В то же время важность дан-ной процедуры не вызывает сомнений.По мнению А. Л. Тахтаджяна (1974): «Вид представляет собой важней-шую таксономическую категорию не только для систематики, но и для всей биологии вообще. Каждое растение, с которым имеет дело исследователь, должно быть определено с точностью до вида, а во многих случаях даже точнее. Не меньшая точность требуется при хозяйственном или медицин-ском использовании растений, например, в лесном хозяйстве и при сборе лекарственных растений. К сожалению, вид, как, впрочем, и все другие так-сономические категории, с трудом поддается сколько-нибудь точному логи-ческому определению. Очень трудно, в частности, дать такое определение вида, которое одинаково хорошо подходило бы как к растениям, размножа-ющимся половым путем, так и к растениям, размножающимся бесполым путем. В одном случае вид представляет собой систему популяций, а в дру-гом случае он есть система клонов. Но в обоих случаях вид характеризуется некоторой целостностью и определенной биологической обособленностью от других видов. Целостность видов выражается в том, что входящие в их состав клоны или популяции связаны между собой переходами. Как бы ни была велика внутривидовая изменчивость, и как бы резко не различались крайние формы, при наличии достаточного материала всегда можно распо-ложить представителей вида таким образом, что они составят непрерывный ряд форм. Обособленность же вида заключена в том, что даже группа близ-ких видов представляет собой прерывистый, дискретный комплекс, где, как правило, нет переходных форм».Умение точно и эффективно определять видовую принадлежность ис-следуемых организмов очень важно и в эколого-генетических исследова-ниях. В последние десятилетия развитие молекулярных методов дало воз-можность применять молекулярные маркеры для видоидентификации и филогенетических исследований. Конечно, данные методы не могут полно-стью вытеснить классические подходы, но способны эффективно их допол-нить. В основе молекулярных подходов лежит закономерность, согласно которой степень родства между живыми организмами обычно коррелиру-ет с уровнем сходства в гомологичных последовательностях нуклеиновых кислот и белков.Молекулярная филогения использует такие данные для построения фи-логенетического древа, которое отражает гипотетический ход эволюции исследуемых организмов.По своей природе молекулярные маркеры, используемые в таких исследо-ваниях можно подразделить на две группы.К первой группе относятся маркеры, представляющие собой продукты сек-венирования таксономически значимых районов. Ко второй группе относятся Поступила в редакцию 21.10.2010. Принята к публикации 21.12.2010.
Salsola tragus L. (Russian thistle) is a problematic invasive weed in the western United States and a target of biological control efforts. In September of 2007, dying S. tragus plants were found along the Azov Sea at Chushka, Russia. Dying plants had irregular, necrotic, canker-like lesions near the base of the stems and most stems showed girdling and cracking. Stem lesions were dark brown and contained brown pycnidia within and extending along lesion-free sections of the stems and basal portions of leaves. Diseased stems were cut into 3- to 5-mm pieces and disinfested in 70% ethyl alcohol. After drying, stem pieces were placed into petri dishes on the surface of potato glucose agar. Numerous, dark, immersed erumpent pycnidia with a single ostiole were observed in all lesions after 2 to 3 days. Axenic cultures were sent to the Foreign Disease-Weed Science Research Unit, USDA, ARS, Ft. Detrick, MD for testing in quarantine. Conidiophores were simple, cylindrical, and 5 to 25 × 2 μm (mean 12 × 2 μm). Alpha conidia were biguttulate, one-celled, hyaline, nonseptate, ovoid, and 6.3 to 11.5 × 1.3 to 2.9 μm (mean 8.8 × 2.0 μm). Beta conidia were one-celled, filiform, hamate, hyaline, and 11.1 to 24.9 × 0.3 to 2.5 μm (mean 17.7 × 1.2 μm). The isolate was morphologically identified as a species of Phomopsis, the conidial state of Diaporthe (1). The teleomorph was not observed. A comparison with available sequences in GenBank using BLAST found 528 of 529 identities with the internal transcribed spacer (ITS) sequence of an authentic and vouchered Diaporthe eres Nitschke (GenBank DQ491514; BPI 748435; CBS 109767). Morphology is consistent with that of Phomopsis oblonga (Desm.) Traverso, the anamorph of D. eres (2). Healthy stems and leaves of 10 30-day-old plants of S. tragus were spray inoculated with an aqueous suspension of conidia (1.0 × 106 alpha conidia/ml plus 0.1% v/v polysorbate 20) harvested from 14-day-old cultures grown on 20% V8 juice agar. Another 10 control plants were sprayed with water and surfactant without conidia. Plants were placed in an environmental chamber at 100% humidity (rh) for 16 h with no lighting at 25°C. After approximately 24 h, plants were transferred to a greenhouse at 20 to 25°C, 30 to 50% rh, and natural light. Stem lesions developed on three inoculated plants after 14 days and another three plants after 21 days. After 70 days, all inoculated plants were diseased, four were dead, and three had more than 75% diseased tissue. No symptoms occurred on control plants. The Phomopsis state was recovered from all diseased plants. This isolate of D. eres is a potential biological control agent of S. tragus in the United States. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 878717). Nucleotide sequences for the ribosomal ITS regions (ITS 1 and 2) were deposited in GenBank (Accession No. EU805539). To our knowledge, this is the first report of stem canker on S. tragus caused by D. eres. References: (1) B. C. Sutton. Page 569 in: The Coelomycetes. CMI, Kew, Surrey, UK, 1980. (2) L. E. Wehmeyer. The Genus Diaporthe Nitschke and its Segregates. University of Michigan Press, Ann Arbor, 1933.
In October of 2006, dying Salsola tragus L. (Russian thistle, tumbleweed), family Chenopodiaceae, plants were found along the Azov Sea at Chushka, Russia. Approximately 40 plants in the area were diseased and almost 80% of these were dying. Plants were approximately 1 m tall × 0.5 m wide. Dying plants had irregular, necrotic lesions along the length of the stems. Leaves of these plants were also necrotic. Lesions on stems and leaves were dark brown and usually coalesced. Diseased stems were cut into 3- to 5-mm pieces, disinfested in 70% ethyl alcohol, and then placed onto the surface of potato glucose agar (PGA). Numerous, waxy, subepidermal acervuli with 110 μm long (mean) black setae were observed in all of the lesions after 2 to 3 days. Conidiophores were simple, short, and erect. Conidia were one-celled, hyaline, ovoid to oblong, falcate to straight, and measured 12.9 to 18.0 × 2.8 to 5.5 μm (mean 15.6 × 4.2 μm). Appressoria formed 24 h after placing conidia on a dialysis membrane over 20% V8 juice agar. Appressoria measured 4.0 to 13.9 × 2.4 to 8.8 μm (mean 7.0 × 5.2 μm). These characters conformed to the description of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. (1). A voucher specimen was deposited with the U.S. National Fungus Collections, Beltsville, MD (BPI 878389). Nucleotide sequences for the internal transcribed spacers (ITS 1 and 2) were deposited in GenBank (Accession No. EU530697) and aligned with ITS sequences of two other isolates from S. tragus. There was 100% similarity to each isolate, one from Greece (Accession No. DQ344621) and one from Hungary (Accession No. EU805538). Axenic cultures on PGA were sent to the Foreign Disease-Weed Science Research Unit, USDA, ARS, Fort Detrick, MD for testing in quarantine. Conidia were harvested from 14-day-old cultures grown on 20% V8 juice agar, and healthy stems and leaves of 30-day-old plants of S. tragus (13 plants) were spray inoculated with an aqueous conidial suspension of 1.0 × 106 conidia/ml plus 0.1% v/v polysorbate 20. Another 13 control plants were sprayed with water and surfactant without conidia. Plants were placed in an environmental chamber at 100% humidity for 16 h in the dark at 25°C. After approximately 24 h, all plants were transferred to a greenhouse at 20 to 25°C, 30 to 50% relative humidity, and natural light augmented by 12-h light periods with 500 W sodium vapor lights. Lesions developed on stems of all inoculated plants after 7 days. After 14 days, nine plants were dead and all inoculated plants were dead after 3 weeks. No symptoms developed on control plants. C. gloeosporioides was reisolated from stem pieces of all inoculated plants, and the morphology of the reisolated pathogen was the same as that of the initially isolated pathogen. To our knowledge, this is the first report of anthracnose caused by C. gloeosporioides on S. tragus in Russia. Reference: (1) B. C. Sutton. Page 15 in: Colletotrichum Biology, Pathology and Control. J. A. Bailey and M. J. Jeger, eds. CAB International, Wallingford, UK, 1992.
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