Use of RNAi to Obtain Ultra-low Gossypol Cottonseed to Enhance Global Food and Feed Security

Global cottonseed production can potentially provide the protein requirements for hundreds of millions of people per year; however, it remains an underutilized resource because of the presence of toxic gossypol within seed glands. Therefore, elimination of gossypol from cottonseed has been a long-standing goal of geneticists.  We have used RNAi to disrupt gossypol biosynthesis in the cottonseed by interfering with the expression of the delta-cadinene synthase (dCS) gene during its development. The Ultra-low Gossypol Cottonseed (ULGCS) trait is stable and heritable. Results from enzyme activity and molecular analyses on developing transgenic embryos were consistent with the ULGCS phenotype observed in the mature seeds.  Importantly, the levels of gossypol and related terpenoids in the foliage and floral parts were not diminished, and thus their potential function in plant defense against insects and diseases remained intact. The stability of the engineered trait has been confirmed by evaluation of several lines over five generations in the greenhouse and also under field conditions.  No adverse effects on fiber/seed yield or quality were observed in the engineered plants. Further, we have obtained molecular and biochemical evidence showing that the germinating, RNAi seedlings are capable of launching terpenoid-based defense response when challenged with pathogens.  Thus, the “silenced-state” of the dCS gene that existed in the seed, does not leave a lasting, residual effect that can interfere with the normal functioning of the cotton seedling during germination.  The use of ULGCS as food or feed has the potential to significantly impact global food security.