Characterizing the role of ferulate-5-hydroxylase (F5H) gene in altering sorghum defense against sugarcane aphids

Sorghum, a major cereal crop grown worldwide for food, feed, and/or fuel, is attacked by sugarcane aphid (SCA; Melanaphis sacchari), a devastating pest of sorghum in the United States. Lignin, a complex heterogeneous polymer present in nearly all plant cell walls, plays a critical role in protecting plants from biotic stresses. However, little is known about how lignin modifications in sorghum affect its resistance to aphids. The interaction between sorghum and SCA has uncovered a role for the sorghum ferulate-5-hydroxylase (F5H) gene, one of the key genes involved in lignin biosynthesis. We found that F5H expression was induced in response to SCA infestation. No-choice and choice aphid bioassays revealed that overexpression of F5H (F5H-OE) provided enhanced susceptibility compared to wild-type (WT; RTx430) plants. Comparison of SCA feeding behavior using the Electrical Penetration Graph (EPG) technique showed that the SCA spent more time feeding from the sieve elements of F5H-OE plants than WT plants. Additionally, we did not observe changes in total lignin levels on WT and F5H-OE plants before and after SCA infestation for 7 days, suggesting that lignin accumulation may not be a contributor to altered resistance to SCA in F5H-OE plants. Overall, our study provides vital information about the lignin biosynthesis pathway in sorghum that can be targeted for altering resistance to aphids and thus aid in developing novel and sustainable strategies for pest control.