Unveiling the dual role of phenylpropanoid pathway genes in soybean defense against white mold

White mold, caused by Sclerotinia sclerotiorum, is a devastating soybean fungal disease and was reported as the third most destructive soybean disease in the U.S., resulting in an estimated 12 million bushels yield loss in 2022. Plants defend against pathogens by producing antimicrobial compounds. Previous studies suggest that the phenylpropanoid pathway plays a key role in soybean defense against white mold. This study focuses on two gene families in this pathway: phenylalanine ammonia-lyases (GmPALs) and cinnamyl alcohol dehydrogenases (GmCADs). GmPALs convert phenylalanine to cinnamic acid, while GmCADs catalyze the conversion of hydroxycinnamoyl aldehydes to alcohols, which is critical for lignin biosynthesis.  In vitro studies revealed that purified cinnamic acid, coniferaldehyde, and sinapaldehyde inhibit S. sclerotiorum growth. Genome analysis identified eight GmPALs and thirteen GmCADs in soybean, and time-course qRT-PCR revealed differential expression of these genes in infected plants. Functional validation through transient overexpression in Nicotiana benthamiana revealed contrasting roles: specific GmPALs enhanced resistance, while certain GmCADs increased susceptibility. These findings highlight the dual role of phenylpropanoid pathway genes in balancing antimicrobial production and lignification. This work identifies GmPALs and GmCADs as promising targets for breeding white mold resistant cultivars, offering a sustainable genetic strategy to reduce reliance on chemical controls and mitigate yield losses in soybean production.