High lysine and high protein-containing salinity-tolerant rice grains (Oryza sativa cv IR64)

Lysine cannot be synthesized by the human body, and it. is, therefore, an indispensable amino acid in the human that must be consumed in adequate amounts to prevent disease. Unfortunately, lysine is not abundant in many important food sources such as rice grains. Efforts to fortify rice and other monocotyledonous crops with high lysine have proved to be challenging because of their effects on plant growth. The present study was designed to avoid the problems that are often encountered in engineering lysine metabolism. We generated different over-expression constructs for the key anabolic enzyme, dihydrodipicolinate synthase (DHDPS and cdapA) and knockdown (KD) constructs for the catabolic enzyme-lysine ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH), with expression under the control of either the CaMV35S promoter or the endosperm-specific glutelinD1 promoter. The use of the endosperm-specific promoter together with the lysine feedback-insensitive cdapA for over-expression provides distinct advantages, as does silencing of LKR/SDH under the control of this promoter. Rice plants produced by over-expressing cdapA together with silencing of LKR/SDH showed a 58% increase in grain lysine content, as well as higher amounts of total seed protein levels. Moreover, the transgenic seedlings were more tolerant to salinity. These results demonstrate that it is possible to generate high lysine stress-tolerant rice varieties, which have the potential to reduce the need for dietary supplementation.