Transgenic analysis of maize endosperm metabolism

Abstract

Maize seeds provide a major component of the calories in the human diet, are critical as a feed source in animal agriculture, and are an important source of biorenewable raw materials. Endosperm tissue accounts for approximately 80% of seed weight, and is the site where carbohydrate and protein storage end products are produced in this net anabolic system. Sucrose supplied from photosynthetic tissues of the maternal plant is transported to growing seeds where it is divided between catabolic pathways that generate ATP and anabolic biosynthetic processes that utilize ATP to generate starch and storage proteins. Considering the high degree of ATP requirement, the fact that maize endosperm is an extremely hypoxic environment raises questions about how energy is generated, and the net efficiency of the system for product formation. This project tested the hypothesis that fully oxidative metabolism is not required for normal kernel development, and accordingly that ATP is generated exclusively or substantially through fermentative processes. To do so, RNAi technology was utilized to inactivate the 2‐oxoglutarate dehydrogenase (ODH) step of the citric acid cycle. T‐DNA vectors were constructed that expressed a double stranded RNA structure containing sequences homologous to both of the maize mRNAs encoding the E2 subunit of this enzyme. Highly active, tissue specific promoters were used to restrict the effects of the transgene exclusively to endosperm tissue. Plants were generated containing the anti‐ODH transgene, and subsequent crosses have established segregating populations of sibling kernels that either contain or lack that element. ODH activity and protein abundance in endosperm tissue will be measured to verify that the transgene is effective in inactivating the targeted enzyme activity. Subsequently, segregating kernel populations will be compared regarding growth rate over the course of development, mature kernel weight and composition, and global metabolite profiles. These studies will reveal the extent to which ODH is required for starch and storage protein synthesis to proceed in developing maize endosperm. This will reveal whether normal ATP generation in this tissue requires oxidative processes or, alternatively, whether fermentative processes can be sufficient to provide the energy required for the massive amount of starch and protein synthesis that makes maize such an important agronomic resource. Answering this question will enable future efforts to improve maize yields and grain quality.Support or Funding InformationThis research was supported by NSF award 1517256 to A.M.M. and T.A.H.‐B.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.