Balasulojini Karunanandaa

Identification and characterization of an Arabidopsis homogentisate phytyltransferase paralog

Tocochromanols (tocopherols and tocotrienols) are micronutrients with antioxidant properties synthesized by photosynthetic bacteria and plants that play important roles in animal and human nutrition. There is considerable interest in identifying the genes involved in tocochromanol biosynthesis to allow transgenic modification of both tocochromanol levels and tocochromanol composition in agricultural crops. The first committed reaction in tocopherol biosynthesis is the condensation of homogentisic acid (HGA) with phytyldiphosphate or geranylgeranyldiphosphate, catalyzed by the homogentisate phytyltransferase (VTE2) or by the homogentisate geranylgeranyl transferase (HGGT). In this study, we describe the identification of conserved amino acid sequences within VTE2 and HGGT and the application of these conserved sequences for a motif analysis resulting in the discovery of a VTE2-paralog in the Arabidopsis genome. We designated this new gene VTE2-2 and renamed the old VTE2 to VTE2-1. Seed-specific expression of VTE2-2 in Arabidopsis resulted in increased seed-tocopherol levels, similar to the transgenic expression of VTE2-1. Bioinformatics analysis revealed that VTE2-2 is conserved in both monocotyledonous and dicotyledonous plants and is distinct from VTE2-1 and HGGT.

Expression of a Streptomyces 3-hydroxysteroid oxidase gene in oilseeds for converting phytosterols to phytostanols

Plant sterols and their hydrogenated forms, stanols, have attracted much attention because of their benefits to human health in reducing serum and LDL cholesterol levels, with vegetable oil processing being their major source in several food products currently sold. The predominant forms of plant sterol end products are sitosterol, stigmasterol, campesterol and brassicasterol (in brassica). In this study, 3-hydroxysteroid oxidase from Streptomyces hygroscopicus was utilized to engineer oilseeds from rapeseed (Brassica napus) and soybean (Glycine max), respectively, to modify the relative amounts of specific sterols to stanols. Each of the major phytosterols had its C-5 double bond selectively reduced to the corresponding phytostanol without affecting other functionalities, such as the C-22 double bond of stigmasterol in soybean seed and of brassicasterol in rapeseed. Additionally, several novel phytostanols were obtained that are not produced by chemical hydrogenation of phytosterols normally present in plants.

Breeding and Biotech Approaches Towards Improving Yield in Soybean

Soybean (Glycine max (L.) Merrill) is the most widely cultivated oilseed crop accounting for more than 50 % of the world’s oilseed production. Yield gain in soybean estimated to be 0.5–0.7 % per year in North America has been driven by the adoption of agronomic or management practices and genetic improvement. While genetic improvement through breeding will continue to play a significant role in enhancing yield by the development of cultivars adapted to a wide range of latitudes, biotech traits such as enhanced insect protection and weed control contribute indirectly to yield improvement. An understanding of physiological traits associated with genetic gain in yield offers vast opportunities for further advances in yield improvement. Potential targets for genetic improvement include source capacity (leaf area index, leaf area duration, carbon and nitrogen assimilation, and dry matter partitioning), sink strength (number of primary and secondary yield components, seed-filling rate and duration), and tolerance to suboptimal conditions (water limitation and high/low temperature). Manipulating single or multiple traits using breeding and biotechnology approaches will help to improve intrinsic yield potential and yield stability traits in soybean. Application of multiple technologies to improve yield gain is vital, with the changing climatic conditions and increasing global demand for food and feed.