Medicinal Plant Research at Crossroads: Biotechnological Approaches for Conservation, Production and Stability in Tissue Cultures and Regenerated Plants

Medicinal plants are treasures of nature with almost never-ending resource of unlimited, diverse, complex and valuable natural compounds with a variety of pharmacological properties. They are used worldwide by all human beings to maintain and restore good health since ancient times. The cumulative effect of heterogeneous distribution and availability throughout the world, anthropogenic interferences like habitat destruction, overexploitation due to increasing demand, unsustainable harvesting practices from the wild, introduction of exotic species, climatic changes, lack of knowledge about medicinal properties and domestication, less agronomical preference in comparison with food crops, weakening of biodiversity protection laws and/or tendency to undermine these laws by modern socio-economic forces are responsible for the loss of medicinal plant biodiversity. Classical plant tissue culture (PTC)-based biotechnological approaches have been efficiently utilized as sustainable platforms for the conservation of endangered, disease-prone and recalcitrant medicinal plant species via in vitro micropropagation and in vitro production of pharmaceutically important bio-active phytochemicals in different transformed and/or non-transformed cells, organs or regenerated plants that effectively decrease harvesting pressure from wild populations of medicinal plants. Advancement in genomics, transcriptomics, proteomics, nanoscience and synthetic biology in recent times have started to revolutionize medicinal plant research in many dimensions where PTC techniques play very important role for the implementation of these modern fields of science by providing constant aseptic control culture condition and better scope to utilize totipotency in comparison with wild cultivation. Hairy root culture, ploidy engineering, metabolic pathway engineering, transgenic plant development, large-scale production in bioreactors, application of Zinc-finger nucleases, TALENs and CRIPR/Cas9 are promising new biotechnological approaches. In spite of various applications and advantages of the PTC techniques, the broader commercial utilization of in vitro techniques as an important tool for the germplasm conservation of threatened commercially important medicinal plant species via mass proliferation and industrial production of SMs can be challenged by genetic, phenotypic and phytochemical instability often developed by somaclonal variations in long-term in vitro culture. The present paper reviews the recent (from 2010 upto June 2020) achievements in PTC research for conservation of medicinal plants, production of important SMs, and the stability of in vitro cultures along with case studies of two endangered species, Podophyllum hexandrum and Rauvolfia serpentina. There are immense opportunities to produce pharmaceutical important SMs with minimal threat to the biodiversity by the application of suitable conventional and upcoming PTC techniques along with screening for stability.