Environmentally responsive QTL controlling surface wax load in switchgrass

Authors: Bragg, Jennifer; Tomasi, Pernell; ZHANG, LI - University Of Texas At Austin; Williams, Tina; Wood, Delilah - De; LOVELL, JOHN - Hudsonalpha Institute For Biotechnology; HEALY, ADAM - Hudsonalpha Institute For Biotechnology; SCHMUTZ, JEREMY - Hudsonalpha Institute For Biotechnology; BONNETTE, JASON - Hudsonalpha Institute For Biotechnology; Cheng, Prisca; Chanbusarakum, Lisa; JUENGER, THOMAS - University Of Texas At Austin; Tobias, Christian

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2020
Publication Date: 8/14/2020
Citation: Bragg, J.N., Tomasi, P., Zhang, L., Williams, T.G., Wood, D.F., Lovell, J.T., Healy, A., Schmutz, J., Bonnette, J.E., Cheng, P.K., Chanbusarakum, L.J., Juenger, T., Tobias, C.M. 2020. Environmentally responsive QTL controlling surface wax load in switchgrass. Theoretical and Applied Genetics. 1-9. https://doi.org/10.1007/s00122-020-03659-0.
DOI: https://doi.org/10.1007/s00122-020-03659-0

Interpretive Summary: A waxy covering on the surfaces of plants helps prevent water loss and is also a defensive barrier against excessive heat and UV light damage. In switchgrass the underlying genetic basis for production of this waxy covering is now beginning to be studied using genetic linkage mapping populations, mutations, and evidence from model plant species. This work has uncovered three genetic regions that control leaf surface wax in a large switchgrass mapping population. Because the population’s leaf wax was measured in multiple locations and years the influence by different environments on this trait was quantified. Differences in chemical composition and surface micro-topology of the waxy layer were described for the population’s founders that likely represent environmental adaptation to specific local environments.

Technical Abstract: The C4 perennial grass Panicum virgatum (switchgrass) is a native species of the North American tallgrass prairie. This adaptable plant can be grown on marginal lands and is useful for soil and water conservation, biomass production, and as a forage. Two major switchgrass ecotypes, lowland and upland, differ in a range of desirable traits and the responsible underlying loci can be localized efficiently in a pseudotestcross design. An outbred 4WCR mapping population of 750 F2 lines was used to examine the genetic basis of differences in leaf surface wax load between two lowland (AP13 and WBC) and two upland (DAC6 and VS16) tetraploid cultivars. Leaf surface wax load is associated with heat and drought tolerance, UV protection, and defense against pathogens. The objective of our experiments was to identify wax compositional variation among the population founders and to map underlying loci responsible for surface wax variation across environments. GCMS analyses of surface wax extracted from 4WCR F0 founders and F1 hybrids reveal higher levels of wax in lowland genotypes and also show quantitative differences of ß-diketones, primary alcohols, and other wax constituents. The full mapping population was sampled over two seasons from four field sites with latitudes ranging from 30 to 42 °N, and leaf surface wax was measured. We identified 3 high confidence QTL, of which 2 displayed significant GxE effects. Over 60 candidate genes underlying the QTL regions showed similarity to genes in either Arabidopsis or barley known to function in wax synthesis, modification, regulation, and transport.