The herbivore-inducible coumarate-CoA ligase 5 (Zm4CL5) in maize contributes to the production of non-lignin phenylpropanoids.

Maize coumarate-CoA ligase gene expression is differentially regulated by different biotic stresses, and Zm4CL5 is induced by fall armyworm herbivory and impacts plant growth. The phenylpropanoid pathway is important for the synthesis of numerous compounds involved in plant growth and stress resilience, including lignin and flavonoids. The last common step in the core phenylpropanoid pathway is the enzyme 4-coumarate:CoA ligase (4CL). Maize (Zea mays) has five 4CL genes, four of which (Zm4CL1-4) are type I (lignin-associated 4CLs), while one (Zm4CL5) is a type II (non-lignin-associated 4CL). In maize, it is not known which, if any, 4CL genes are involved in plant defense. Here we show that infection with the fungal pathogen Cochliobolus heterostrophus alters the expression of the type I genes, while herbivory by Spodoptera frugiperda induces the type II gene Zm4CL5. A knock-down mutant of Zm4CL5 displayed altered accumulation of flavonoids and other non-lignin phenylpropanoids, as well as increased plant height, revealing a role for Zm4CL5 both in plant growth and in non-lignin phenylpropanoid production. These data indicate that 4CL genes in maize play differential roles in growth and in the defense against different biotic stressors.