TOWARD CONTROL STRATEGIES OF EMERGING PATHOGENS AND NEMATODES OF COTTON
Location: Cotton Pathology Research
Title: Ultra-low gossypol cottonseed: generational stability of the seed-specific, RNAi mediated phenotype and resumption of terpenoid profile following seed germination
Submitted to: Plant Biotechnology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 2011
Publication Date: September 1, 2012
Citation: Rathore, K.S., Sundaram, S., Sunilkumari, G., Campbell, L.M., Puckhaber, L.S., Marcel, S., Palle, S., Stipanovic, R.D., Wedegaertner, T.C. 2012. Ultra-low gossypol cottonseed: Generational stability of the seed-specific, RNAi mediated phenotype and resumption of terpenoid profile following seed germination. Plant Biotechnology Journal. 10(2):174-183.
Interpretive Summary: Cottonseed is a source of a high quality protein, but it cannot be utilized for human consumption because of the presence of a toxic compound called gossypol. However, gossypol and related compounds occur in the foliage, roots and bolls. These compounds help protect the plant from attack by insects and plant pathogens. Earlier we reported development of plants that are genetically modified such that they produce very low levels of gossypol in the seed, but produce normal levels of gossypol and related compounds in the foliage, roots and bolls a month or more after seed germination. We now show that like non-transgenic plants, the transgenic plants show normal levels of these compounds during early growth of the roots and true leaves. In addition, like non-transgenic plants the transgenic plants produce these protective compounds when they are attacked by plant pathogenic organisms. This demonstrates that the transgenic plants should be as resistant to pathogens as the non-transgenic plants.
Cottonseed, containing 22.5% protein, remains an under-utilized and under-valued resource due to the presence of toxic gossypol. RNAi-knockdown of beta-cadinene synthase gene(s) was used to engineer plants that produced ultra-low gossypol cottonseed(ULGCS). In the original study, we observed that RNAi plants, a month or older, maintain normal complement of gossypol and related terpenoids in the roots, foliage, floral organs, and young bolls. However, the terpenoid levels and profile of the RNAi lines during the early stages of germination, under normal conditions and in response to pathogen exposure, had not been examined. Results obtained in this study show that during the early stages of seed rmination/seedling growth, in both non-transgenic and RNAi lines, the tissues derived directly from bulk of the seed kernel (cotyledon and hypocotyl) synthesize little, if any new terpenoids. However, the growing root tissue and the emerging true leaves of RNAi seedlings showed normal, wild-type terpenoid levels. Biochemical and molecular analyses showed that pathogen-challenged parts of RNAi seedlings are capable of launching a terpenoid-based defense response. Nine different RNAi lines were monitored for five generations. The results show that, unlike the unstable nature of antisense-mediated low seed-gossypol phenotype, the RNAi-mediated ULGCS trait exhibited multi-generational stability.