Location: Chemistry ResearchTitle: Commercial hybrids and mutant genotypes reveal complex protective roles for inducible terpenoid defenses
|Sims, James - Eth Zurich|
|Huffaker, Alisa - University Of California|
|Schmelz, Eric - University Of California|
Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2017
Publication Date: 1/18/2018
Citation: Christensen, S.A., Sims, J., Vaughan, M.M., Hunter III, C.T., Block, A.K., Willett, D.S., Alborn, H.T., Huffaker, A., Schmelz, E.A. 2018. Commercial hybrids and mutant genotypes reveal complex protective roles for inducible terpenoid defenses. Journal of Experimental Botany. doi:10.1093/jxb/erx495.
Interpretive Summary: Crop loss due to pathogen threats is a recurring global problem, leading to billions of dollars in reduced yield and revenue annually. Gray leaf spot (GLS) is a damaging foliar disease of maize that has been documented in many sub-tropical and tropical regions of the world. Symptoms are matchstick-shaped necrotic lesions with a gray tint on the leaf surface. Resistance to GLS and other maize pathogens often requires the action of many defensive genes (e.g. fungal cell wall damaging and antibiotic producing genes), a phenomenon referred to as quantitative disease resistance. While many studies have described the genetic regions responsible for disease resistance, identifying the specific genes that confer quantitative disease resistance in maize is currently a major challenge. Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, in collaboration with researchers from South Africa and Belgium, investigated the genetics of a large population of maize derived from resistant (CML444) and susceptible (SC Malawi) parent lines in search for specific genes responsible for resistance and susceptibility to GLS. As a result of our analysis, we identified a specific maize gene, termed COI-1, which plays a significant role in controlling GLS disease severity. The screening for and incorporation of this gene into germplasm will contribute to strategies that improve disease resistance in maize.
Technical Abstract: Despite long-term efforts to characterize inducible antimicrobial defenses in crops, the presence of acidic phytoalexins in maize was only recently established with the discovery of kauralexins and zealexins. Given the predicted existence of additional phytoalexins, we profiled terpenoids in maize tissues infected with pathogenic fungi and identified a novel zealexin, termed zealexin A4 (ZA4). Evaluation of zealexins, kauralexins, and other defense metabolites in commercial hybrid lines (CHLs) revealed distinct defense accumulation patterns in pathogen-infected tissues. ZA4 was strongly elicited by Cochliobolus heterostrophus but only weekly induced by Fusarium graminearum and Colletotrichum graminicola. ZA4 had strong antimicrobial activity against F. graminearum, but unexpectedly promoted C. heterostrophus and C. graminicola fungal growth in liquid culture. Overall, a negative correlation was observed between total phytoalexin production and fungal growth. Statistical analysis showed kauralexin A3 (KA3) and the drought inducible hormone abscisic acid (ABA) to have the strongest impacts on fungal growth suppression. Anther Ear 2 mutants deficient in kauralexins demonstrated significantly improved C. heterostrophus and F. verticillioides growth compared to respective wild-types. Furthermore, drought-induced ABA reduced fungal proliferation in stems. Current results highlight the widely occurring defense functions for maize terpenoids in diverse commercial lines and selective activities on different fungal pathogens.