Tissue culture and genetic transformation of safflower (Carthamus tinctorius L.)

Abstract

Safflower belonging to the family Asteraceae is an underutilized industrial crop of semi-arid regions. The oil is valued therapeutically due to its high degree of poly-unsaturation apart from its use in cosmetics, in the manufacture of urethane, resins, linoleum, and high quality emulsion paints. In vitro culture techniques, such as direct shoot organogenesis and somatic embryogenesis are successful from cotyledonary leaf explants. Direct and callus- mediated shoot regeneration from seedling tissues and anthers are also described. Cotyledon explant is highly responsive in adventitious shoot regeneration on medium supplemented with BA + NAA or TDZ + NAA. Somatic embryos were induced directly on adaxial surface of the cotyledonary leaves on Murashige and Skoog (MS) medium containing 5.37-10.74 μM NAA and 2.22 μM BA within 8-10 days of culture. Somatic embryo development was asynchronous and strongly influenced by auxin type and concentration. Various factors such as genotype, explant age, carbon source, and ethylene affected somatic embryogenesis frequency, number of somatic embryos per responding explant and somatic embryo maturation and germination. Medium containing 8.87 μM BA and 2.69 μM NAA promoted shoot regeneration from anthers and microspores. Genetic engineering has the potential to accelerate crop improvement programmes and has yielded encouraging results in several crop plants. In safflower, Agrobacterium-mediated transformation protocols have been reported for both Indian and American cultivars. Transformation studies were limited to constructs harbouring commonly used reporter (uidA, GFP) and selectable marker genes (nptII). The studies indicated influence of co-cultivation conditions, Agrobacterium tumefaciens strain, type of explant, genotype, etc. Transgene expression was confirmed with transient assays by GUS expression and molecular analysis through PCR and Southern hybridization assays of the primary transformants. Despite the high frequency of shoot regeneration from transformed tissues (15-34.3 %), rooting of transformed shoots is yet to overcome. So far, safflower has been used for the production of valuable plant made pharmaceuticals through agro-infection. However, the tissue culture based transformation protocols are yet to be exploited for the development of transgenics with agronomically desirable traits.