Plants as bioreactors for the production of biopesticides

Abstract

Plant bioreactors are attractive production systems of secondary metabolites currently usedas medicines for the treatment of different diseases, as additives in food, industrial productsand cosmetics, and as pesticides in the agricultural sector. Some of the metabolites producedby plants include flavonoids, alkaloids, quinones, coumarins, tannins, phenolics, saponins,and essential oils (EOs) (Upadhyay and Singh 2021). EOs are hydrophobic substances ofcomplex mixtures of volatile organic compounds (VOCs), i.e. compounds that evaporate atnormal temperatures and pressures, which are released from specific plant tissues andorgans, such as flowers, stems, seeds, and roots. Groups of VOCs as main constituents ofEOs are monoterpenes (10-carbon isoprenoids), sesquiterpenes (15-carbon isoprenoids),phenylpropanoids, and benzenoids. In addition, plant tissues can produce volatile aldehydes and their corresponding acids, alcohols, and ketones (Pandey et al. 2017). One of themain functions of these VOCs involve defending plants from insect herbivores and microbial pathogens, such as filamentous fungi and bacteria. Because of these properties, EOsand/or their pure components have been long recognized as effective pesticides, in agreement with studies reporting the potential use of EOs against microbial and insect pests.However, the number of commercial products is low, with only a handful of EOs or purecompounds used as ingredients in manufactured pesticidal formulations. One of the mainFernanda Achimón1,2, Vanessa A. Areco3, Vanessa D. Brito1,2, MaríaL. Peschiutta1,2, Carolina Merlo1,2,4, Romina P. Pizzolitto1,2,4, JulioA. Zygadlo1,2,5, María P. Zunino1,2,5, and Alejandra B. Omarini61 Área de Bioplaguicidas, Instituto Multidisciplinario de Biología Vegetal (IMBIV-CONICET), Córdoba, Argentina 2 Área Aromas y Pigmentos, Instituto de Ciencia y Tecnología de los Alimentos (ICTA), Universidad Nacional de Córdoba(UNC), Córdoba, Argentina3 Instituto Multidisciplinario de Investigación y Transferencia Agroalimentaria y Biotecnológica (IMITAB-CONICET) -Universidad Nacional de Villa María (UNVM), Córdoba, Argentina4 Departamento de Recursos Naturales, Cátedra de Microbiología Agrícola, Universidad Nacional de Córdoba, Córdoba, Argentina5 Departamento de Química, Cátedra de Química Orgánica, Universidad Nacional de Córdoba, Córdoba, Argentina6 Laboratorio de Biotecnología Fúngica y de los Alimentos, Asociación para el Desarrollo de Villa Elisa y Zona (ADVEZ) -Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Entre Ríos, ArgentinaPlants as Bioreactors for the Production of Biopesticides338 14 Plants as Bioreactors for the Production of Biopesticidesobstacles for the massive application of EOs is that they are synthesized by plants in smallquantities. In addition, most plant species are annual, yielding in a single harvesting season,a mass whose weight represents a low percentage of the whole plant. The amount of EOs inplant seeds, flowers, stems, and roots is estimated to range from 0.1 to 10% of EO (v/w).Furthermore, a single compound can comprise 40?90% of EO, and it is usually not the mostuseful one (Gounaris 2010). Accordingly, affording desirable EOs and pure VOCs fromplants can be an expensive and difficult process. In this context, biotechnology attempts tofacilitate the production of VOCs and EOs, and therefore, reduce the market cost of EObased products. Most efforts have been devoted to developing transgenic plants through thegenetic modification of certain biosynthetic pathways of host plants responsible for the synthesis of the desired EOs and/or VOCs. Other attempts have been made to produce desiredVOCs by biotransformation of cheaper precursors into added value products, either by isolated enzyme preparation or use of organisms such as fungi, yeasts, and bacteria.The present chapter will discuss the use of plants as bioreactors to produce EOs withpesticidal properties for the agricultural area. First, we will focus on the different mechanisms of genetic manipulation of aromatic plants currently used to increase the yield ofEOs and their pure components. Second, we will explore the use of different EOs as insecticides, bactericides, and fungicides reported over the past five years. Third, we will addresssome aspects of the biotransformation of volatile precursors into new bioactive molecules.Finally, we will discuss and compare the production of EOs with transgenic plants andplant cell cultures