D3091: (1st Place) Altering lignin biosynthetic pathway modulates sorghum defense against sugarcane aphids

Sorghum (Sorghum bicolor), arguably the world’s most important multi-purpose monocot crop grown for food, feed, and/or fuel, suffers severe yield losses due to attack by phloem-feeding insects that limit plant productivity by removing phloem sap, altering source-sink patterns, and vectoring plant viruses. Lignin, an organic polymer compound present in nearly all plant secondary cell walls, plays a critical role in protecting plants from biotic stresses. However, little is known about how lignin modifications in sorghum will affect plant protection against sugarcane aphid (SCA; Melanaphis sacchari), a critical pest throughout the sorghum production regions of the U.S. Ferulate-5-hydroxylase (F5H) in the monolignol biosynthetic pathway converts coniferaldehyde into 5-hydroxy-coniferaldehyde, which further leads to the synthesis of S-lignin monomers. Overexpressing the F5H gene (F5H OE) in sorghum alters the composition of each lignin monomer and thereby the properties of lignin. SCA feeding on sorghum plants induced the expression of F5H. Additionally, F5H OE plants provided enhanced resistance to SCA compared with wild-type sorghum plants in both no-choice (antibiosis) and choice (antixenosis) bioassays. Comparison of SCA feeding behavior using Electrical Penetration Graph (EPG) revealed that SCA took significantly more time to reach the first sieve element phase (SEP) and spent less time in the SEP of F5H OE plants compared with wild-type sorghum plants. Taken together, our results suggest that the monolignol pathway is involved in promoting plant defense against SCA and F5H is a key component of this defense mechanism.