|Wagner, Tanya - Texas A&M Agricultural Experiment Station|
|Bell, Alois - Al|
|Magill, Clint - Texas A&M University|
Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Abstract Only
Publication Acceptance Date: 11/4/2016
Publication Date: N/A
Technical Abstract: The production of sesquiterpenoids in cotton tissues contribute to the plant’s constitutive and inducible defense against pathogens. In roots, gossypol (G), desoxyhemigossypol (dHG), hemigossypol (HG), and their methylated derivatives MG, DMG, dMHG, and MHG are the main defense compounds. dHG is the most toxic, followed by dMHG, HG, MHG, with the non-methylated compounds being more toxic to fungal spores and hyphae than their methylated counterparts. The enzyme, desoxyhemigossypol-6-O-methyltransferase (dHG-6-OMT), is responsible for the conversion of dHG to dMHG. We hypothesized that knocking down the expression of dHG-6-OMT in G. hirsutum via RNAi would increase levels of dHG and HG in roots, and that these plants would show increased resistance to soil borne pathogens. We generated eight independently transformed RNAi lines. All lines suppressed the methylation of sesquiterpenoids in roots resulting in methylation between 0 and 58% of WT levels. Data for one line is presented here. In unchallenged plant roots, the amount of methylated compounds in RNAi-containing plants is reduced to 3% of WT levels. Although HG, dHG, and gossypol levels are increased 1.6, 1.8, and 1.3X, respectively, in the RNAi-containing plants compared to WT, the total amount of phytoalexins present in roots is reduced almost by half in the RNAi-containing plants due to the blockage of methylated derivatives’ production. Thus, feed-back regulation may prevent the continual synthesis and build-up of HG and dHG. The RNAi plants were tested for increased resistance to Fusarium oxysporum f. sp. vasinfectum (Fov) race 4, a root rot pathotype. Homozygous WT and RNAi cotton plants were inoculated with a highly, moderately, or weakly virulent race 4 isolate using a soil drench method. Plant measurements were taken at 6 weeks post inoculation. No significant differences between the RNAi-containing plants and the WT sibs were observed, indicating that the amount and compositional changes of gossypol-related compounds in roots of RNAi plants did not influence plant resistance to Fov race 4. Thus, the toxicity gained by small increase in the amount of more toxic non-methylated phytoalexins maybe not enough to compensate the toxicity lost by almost 97% reduction of the methylated derivatives accounting 50% of the total amount of phytoalexins. Experiments are currently underway to test if RNAi plants are more resistant to vascular competent pathotype Fov pathogens.