|WAGNER, TANYA - Texas A&M University|
|CAI, YINGFAN - Henan University|
|Bell, Alois - Al|
|MAGILL, CLINT - Texas A&M University|
Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2019
Publication Date: 1/10/2020
Citation: Wagner, T.A., Cai, Y., Bell, A.A., Puckhaber, L.S., Magill, C., Duke, S.E., Liu, J. 2020. RNAi suppression of a gossypol biosynthetic CYP82D P450 hydroxylase enhances Fusarium wilt disease resistance in cotton. Journal of Phytopathology. 168:103-112. https://doi.org/10.1111/jph.12873.
Interpretive Summary: Cotton plants produce two classes of defense compounds, gossypol and lacinilene, to help protect plants against pathogens and insect pests. Both classes are derived from a common compound, delta cadinene, which can enter one pathway to produce gossypol or another pathway to form lacinilene. We blocked the gossypol pathway using a genetic modification approach known as RNA interference (RNAi) and observed enhanced resistance to a fungal root disease known as Fusarium wilt. Analyses of compounds in the roots revealed that the levels of lacinilene were more than 19-fold higher in the RNAi plants than in non-genetically modified plants. This finding suggests that by blocking the gossypol pathway, more delta cadinene was funneled into the lacinilene pathway, resulting in increased production of lacinilene. We also found the presence of wilt pathogens elicited increased production of lacinilene in the roots. Collectively, these findings shed light on a possible mechanism of wilt disease resistance in cotton and provide a new approach for increasing cotton resistance to Fusarium wilt through manipulation of these defense chemical pathways.
Technical Abstract: Cotton plants produce two classes of terpenoid defense compounds against pathogens and other pests. Both classes are derived from a common sesquiterpenoid precursor '-cadinen-2-one, which enters either the gossypol pathway or the lacinilene pathway. Blocking the gossypol pathway by RNAi suppression of the early pathway biosynthetic enzyme CYP82D hydroxylase resulted in enhanced disease resistance to a Fusarium wilt pathogen. Analyses of root terpenoids revealed no overall increases in products of the gossypol pathway in the roots infected by the wilt pathogen. However, the lacinilene pathway was elicited by the pathogen and the levels of lacinilenes were greater than 19-fold higher in the RNAi plants than in wild type plants. In the pathogen inoculated RNAi plants, the concentrations of DHC and HMC were about 225 'g and 780 'g/g dry roots, respectively, which may have contributed to the inhibition of the fungal invasion. Fungitoxicity testing showed that DHC at 100 'g/ml inhibited growth of the Fusarium wilt pathogen by greater than 93%. Treatment with the phytohormone jasmonic acid failed to elicit production of lacinilene pathway terpenoids in roots of either RNAi or their wild type sibling lines but increased production of gossypol pathway terpenoids with concentrations in RNAi plants 80-97 % less than those in wild type plants. This indicates that induction of the lacinilene pathway is not directly mediated by jasmonic acid signaling and requires other signaling upon perception of the pathogen. These results illustrate possible mechanisms of wilt disease resistance in cotton and provide a new approach to increase host resistance by manipulating these two major cotton chemical defense pathways.