Abstract
Vitamin A deficiency (VAD) is a serious public health problem in South Asia particularly in Bangladesh. Indica rice as a major staple in the country completely lacks vitamin A or compounds with provitamin A activity after milling. The aim of this work was to incorporate provitamin A biosynthesis pathway in endosperm tissue of selected Bangladeshi indica rice. Provitamin A containing rice could provide an easy and convenient solution to overcome VAD on those people who rely predominately on rice as a staple food. Rice is usually milled to remove the oil-rich aleurone layer that turns rancid upon storage, especially in tropical areas. Due to poverty and limited access to more diversified foods, deficiencies of iron, zinc and vitamin A prevail in rice consuming developing countries. In Bangladesh, VAD is a serious public health problem and VAD in preschool children exceeded WHO's cut-off point criterion. A combination of transgenes enabling biosynthesis of provitamin A was introduced in the endosperm of several indica rice cultivars adapted to Bangladesh. As a prerequisite for stable rice transformation several indica rice varieties for tissue culture response was assessed. The most responsive varieties were used for transformation experiments via microprojectile bombardment. The rice seed-specific glutelin promoter (Gt-1 P) was used to drive the expression of phytoene synthase (psy). Lycopene B-cyclase (lcy) and phytoene desaturase (crtl), fused to the transit peptide sequence of the pea-Rubisco small subunit, were driven by the constitutive cauliflower mosaic virus promoter (CaMV35s P). For selection of the putative transformed tissues, hygromycin-B was used as a selectable agent. Molecular and biochemical analysis demonstrated stable integration and expression of the transgenes. HPT-assay showed the functional expression of the selectable marker hph gene. The yellow color of the polished rice grain evidenced the carotenoid accumulation in the endosperm. The color intensity was correlated with estimated carotenoid content by spectrophotometric and HPLC analysis. Homozygocity was enriched for golden indica Bangladeshi rice variety BRRI dhan 29 and progenies of BR827R are in advanced stages. Marker free transgenic BRRI dhan 29 was obtained by conventional cross breeding, which would play an important role in the field-testing of transgenics. Development of provitamin A enriched Bangladeshi rice would be able to play an important role for the prevention of VAD for Bangladeshi community.