Biotechnological Means for Genetic Improvement in Castor Bean as a Crop of the Future

Abstract

Profitable cultivation of castor bean is beset with problems of vulnerability of cultivars and hybrids to a multitude of insect pests and diseases. The presence of the toxic proteins ricin and hyperallergenic Ricinus communis agglutinin (RCA) in the endosperm restricts the use of deoiled seed cake as cattle feed. Due to this crop's low genetic diversity, genetic engineering can be an efficient approach to introduce resistance to biotic and abiotic stresses as well as seed quality traits. Recently, castor oil gained attention as a sustainable second-generation feedstock for biojet fuel that would reduce carbon dioxide emissions. Because of a growing interest in castor oil as a biofuel and the presence of the powerful toxin ricin in its seed, metabolic pathways and regulatory genes involved in both oil and ricin production have been analyzed and characterized. Genetic engineering of castor bean offers new possibilities to increase oil yield and oxidative stability, confers stress tolerance, and improves other agronomics traits, such as reduced plant height to facilitate mechanical harvesting. However, difficulties in tissue culture-based regeneration and poor reproducibility of results are major bottlenecks for genetic transformation of castor bean. Despite advances in tissue culture research over the past four decades, direct or callus-mediated adventitious shoot regeneration systems that are genotype-independent remain a much sought-after goal in castor bean. Genetic transformation attempts to develop insect-resistant and ricin-free transgenic castor bean lines have been based on shoot proliferation from meristematic tissues. This chapter describes new transformation methods under development and the progress achieved so far in genetic engineering of castor bean for agronomically desirable attributes.