Plant Biotechnology of Flavonoids

Abstract

Flavonoids, including anthocyanins are ubiquitous compounds constituting about 5-10% of the known secondary metabolites imparting vivid floral, seed and foliage colors in plants ranging from bryophytes to angiosperms. Plants are specialized in synthesizing and accumulating specific combinations of flavonoids out of a pool of about 5000 known flavonoids implying their adaptive functions. The flavonoid pathway has been well characterized in a few select plants. The genetic and molecular analysis revealed that the pathway is governed by a number of loci dispersed across the plant genome and regulated by distinct regulatory gene families in a temporal and spatial manner. With the rapid growth in molecular and biochemical characterization of the genes and their products it has now become possible to precisely elucidate the role of flavonoids in plant survival. Flavonoids have been implicated in diverse functions such as UV-B protection, signal molecules in plant-microbe symbiotic associations, plant defense response, cold stress response, modulators of hormone response and pollen fertility. In addition, the role of flavonoids as very powerful dietary anti-oxidant supplements in human nutrition is increasingly demonstrated. The review highlights certain structural and functional aspects of flavonoids particularly their role in stress response. Further, recent advances in application of biotechnology tools to manipulate flavonoid pathway in different plants has been described. Flavonoid genes as benign and visible reporters of plant origin in transformation experiments appears to be promising. Studies on transgenic plants carrying genetically engineered flavonoid genes leading to the accumulation of flavonoids by sense over-expression or decrease or elimination by anti-sense suppression respectively, have been used to manipulate plants defense response against bacterial and fungal diseases. Flavonoid biotechnology has become a powerful tool to manipulate flower color in horticulture industry. This review critically evaluates various functions of flavonoids and describes specific instances and strategies of biotechnological manipulation to improve plant performance and value addition.