A. V. Kochetov

Tobacco Transformants Bearing Antisense Suppressor of Proline Dehydrogenase Gene, Are Characterized by Higher Proline Content and Cytoplasm Osmotic Pressure

The antisense suppressor was constructed for proline dehydrogenase gene (PDH; a fragment of PDH from Arabidopsis in antisense orientation and under the control of 35S promoter of cauliflower mosaic virus, CMV). In Nicotiana tabacum SR1 tobacco transformants bearing antisense suppressor for PDH, the proline content and the cytoplasm osmotic pressure were increased. The proline content in these transformants varied, whereas cytoplasm osmotic pressure was stable, which seems to reflect complicated relationships between these characteristics of the plant cell.

PR-proteins with ribonuclease activity and plant resistance against pathogenic fungi

Pathogenesis-related (PR) proteins participate in complex plant defense responses to pathogens. It is known that members of two PR-protein families (PR4 and PR10) exhibit ribonuclease activity in some cases. These proteins were found to be able to inhibit the growth of pathogenic fungi, and ribonuclease activity is necessary for the manifestation of this effect. This paper presents current data on molecular mechanisms governing the antifungal activity of PR-ribonucleases, associated both with their direct cytotoxic impact on pathogen cells and with their possible participation in the induction of plant cell apoptosis and development of hypersensitive reactions (HR).

Transgenic plants tolerant to abiotic stresses

The publications containing data on the generation and study of transgenic plants tolerant to various types of abiotic stresses were analyzed. Mechanisms of plant protection against stresses and genes encoding a wide spectrum of compounds that confer the ability to survive under stress conditions, which cause inhibition of development and are even lethal to control plants are also discussed.

Partial suppression of gene encoding proline dehydrogenase enhances plant tolerance to various abiotic stresses

The role of gene of proline dehydrogenase (PDH) in the maintenance of stress tolerance was investigated using the model transgenic plants of tobacco (Nicotiana tabacum L.) carrying an antisense suppressor of PDH gene (a fragment of Arabidopsis PDH gene under the control of cauliflower mosaic virus 35S promoter in antisense orientation) and notable for a low activity of PDH and elevated content of proline. The progeny of transgenic plants belonging to the 5th generation (T5) with partially suppressed PDH activity was more resistant to various types of stress as compared with the control plants of tobacco, cv. Petit Havana SR-1 (SR1). The seedlings of transgenic lines cultured in Petri dishes on agar media supplemented with stress agents were resistant to high NaCl concentrations (200–300 mM) and water deficit simulated by an increased agar content in the medium (14 g/l) as compared to the control seedlings of cv. SR1. Juvenile plants of transgenic lines grown in pots filled with a mixture of vermiculite and perlite also manifested the higher resistance to water deficit and low temperatures (2°C and −2°C) than the control plants. Thus, the partial PDH suppression correlated with an increase in nonspecific resistance to different types of abiotic stress: salinity, water deficit, and low temperatures. Such transgenic lines of tobacco are promising genetic models for thorough investigation of molecular mechanisms of stress resistance in plants.

Tobacco transformants expressing antisense sequence of proline dehydrogenase gene possess tolerance to heavy metals

Analysis of resistance of genetically modified tobacco plants bearing antisense suppressor of proline dehydrogenase gene and characterized with higher content of proline to elevated concentrations of heavy metals was performed. It was demonstrated that progeny of transgenic plants have high resistance to lead, nickel and cadmium ions.

Evaluation of salt tolerance in Nicotiana tabacum plants bearing an antisense suppressor of the proline dehydrogenase gene

We studied the stress resistance of genetically modified (GM) tobacco plants bearing an antisense suppressor of the gene for proline dehydrogenase. Such plants are characterized by elevated proline content. The progeny of the transgenic plants were shown to have elevated salt tolerance.

Effective expression of the gene encoding an extracellular ribonuclease of Zinnia elegans in the SR1 Nicotiana tabacum plants

Complementary DNA for the extracellular RNase of Zinnia elegans was cloned under control of the cauliflower mosaic virus 35S RNA constitutive promoter and transferred into the Nicotiana tabacum SR1 plants. Primary tobacco transformants were characterized by a high level of RNase activity.

Plant cell wall and mechanisms of resistance to pathogens

A huge variety of phytopathogens (viruses, bacteria, and fungi) are potentially able to infect plant tissues and cause diseases. Numerous plant genes control a complex network of defense mechanisms based on both constitutive and inducible processes. The cell wall is a primary barrier the pathogens have to penetrate to start the infection process. Resistance at the level of the cell wall can prevent invasion of most potential pathogens. The cell wall structure may differ in various plant species. It is based on the network of cellulose microfibrils linked by hemicellulose molecules. In the growing parts of the plant, this network is integrated into the matrix of pectin polysaccharides. In the formed tissues, the cell wall is reinforced with lignin. In addition to polysaccharides, the cell wall contains a significant number of proteins implementing structural and enzymatic functions. The WallProtDB database stores information on many proteins of the cell wall of different plant species. Each of the cell wall components contributes to the formation of resistance to pathogens. The sites of contact with potential pathogens are characterized by the additional strengthening of the cell wall and the accumulation of antimicrobial secondary metabolites. The pathogens secrete enzymes that can break down the components of the cell wall. In response to the attack of microbes the plant produces inhibitors of microbial hydrolytic enzymes. The plant is also able to assess the number of components of the cell wall. For instance, mutants deficient for cellulose normally have an increased level of lignification and an increased defense response. Emerging after the action of microbial enzymes, low-molecular-weight cell wall fragments perform the signal function, enhancing the protective response of the plant. Thus, the cell wall is a dynamic structure, which can prevent the invasion of the majority of potential pathogens and initiate different variants of the immune response. Reconstruction of gene networks that control the structural and functional organization of the cell wall during the growth and under biotic and abiotic stress is crucial for understanding the molecular mechanisms of development and stress resistance. The review deals with the mechanisms of specific and nonspecific resistance of plants to pathogens of different nature, which are related to the cell wall. The cell wall structure and the role of various components in the detecting the invasion of plant pathogens and the induction of defense mechanisms are discussed.

Transgenic expression of Serratia marcescens native and mutant nucleases modulates tobacco mosaic virus resistance in Nicotiana tabacum L.

Extracellular Serratia marcescens nuclease is an extremely active enzyme which non-specifically degrades RNA and DNA. Its antiviral activity was previously shown both in animals and in plants when applied exogenously. Transgenic tobacco plants (Nicotiana tabacum L. cv. SR1) expressing S. marcescens chimeric, mutant, and intracellular mutant nuclease gene variants were regenerated and challenged with tobacco mosaic virus. The transgenic plants exhibited a higher level of resistance to the virus infection than the control non-transgenic plants. The resistance was evidenced by the delay of the appearance of mosaic symptoms and the retarded accumulation of viral antigen. Thus, these results reveal that modulations of both extracellular nuclease activity and intracellular RNA/DNA binding can protect plants against viral diseases.

Tobacco transformants expressing the Medicago truncatula ornithine aminotransferase cDNA

The Medicago truncatula ornithine aminotransferase cDNA was cloned under the potent constitutive 35S RNA promoter of the cauliflower mosaic virus and transferred into the genome of tobacco Nicotiana tabacum SR1 plants. Transformed tobacco plants grew better in salinity stress, but did not differ in proline content under normal or stress conditions from control plants. It was assumed that the role of ornithine aminotransferase in the molecular mechanisms of stress resistance is not associated with additional proline synthesis.