Phenol amide regulator ZmPHT3 targets phloem protein ZmPP2-B8 to enhance maize broad-spectrum disease resistance

Phenol amides (PAs), a class of plant secondary metabolites, play crucial roles in plant defense, yet the genes regulating their biosynthesis and functional mechanisms against pathogens in maize remain poorly characterized. Here, we demonstrated that pathogen infection upregulates ZmPHT3, which encodes a BAHD acyltransferase essential for driving the accumulation of p-coumaroylputrescine (Cou-put), N-caffeoylputrescine (Caf-put), and N-feruloylputrescine N-glucoside (Fer-put-glu). Overexpression of ZmPHT3 boosted the levels of these compounds, consequently suppressing hyphal growth and strengthening resistance. Conversely, disruption of ZmPHT3 diminished PA accumulation, leading to increased hyphal expansion and higher susceptibility. Exogenous application of Cou-put and Caf-put partially restored fungal growth restriction in zmpht3 mutants, confirming the antimicrobial function of PAs. Mechanistically, we found that ZmPHT3 modulates the phloem protein ZmPP2-B8 via 2 distinct pathways: (i) direct protein interaction and (ii) through the action of its enzymatic products. This model is supported by multiple lines of evidence: ZmPHT3 physically interacted with ZmPP2-B8; a catalytically inactive ZmPHT3 variant failed to promote ZmPP2-B8 protein accumulation; and treatment with Caf-put, Cou-put, or Fer-put elevated ZmPP2-B8 protein levels. Silencing ZmPP2-B8 impaired disease resistance, and silencing both ZmPHT3 and ZmPP2-B8 demonstrated that their encoded proteins act synergistically to promote immunity. Furthermore, ZmPHT3 and ZmPP2-B8 cooperatively upregulated lignin biosynthesis and cellulose synthase genes, enhancing cell wall fortification. Our findings unveil a defense mechanism in which pathogen-induced ZmPHT3 promotes accumulation of PAs that function dually as antimicrobial agents and ZmPP2-B8 stabilizers, forming a synergistic module that reinforces the cell wall and broadens the resistance spectrum in maize.