Salicylic acid activates poplar defense against the biotrophic rust fungus Melampsora larici-populina via increased biosynthesis of catechin and proanthocyanidins

Chhana Ullah, Chung-Jui Tsai, Sybille B. Unsicker, Liangjiao Xue, Michael Reichelt, Jonathan Gershenzon, Almuth Hammerbacher
2018 New Phytologist  
Poplar trees synthesize flavan-3-ols (catechin and proanthocyanidins) as a defense against foliar rust fungi, but the regulation of this defense response is poorly understood. Here, we investigated the role of hormones in regulating flavan-3-ol accumulation in poplar during rust infection. We profiled levels of defense hormones, signaling genes, and flavan-3-ol metabolites in black poplar leaves at different stages of rust infection. Hormone levels were manipulated by external sprays, genetic
more » ... gineering, and drought to reveal their role in rust fungal defenses. Levels of salicylic acid (SA), jasmonic acid, and abscisic acid increased in rust-infected leaves and activated downstream signaling, with SA levels correlating closely with those of flavan-3ols. Pretreatment with the SA analog benzothiadiazole increased flavan-3-ol accumulation by activating the MYB-bHLH-WD40 complex and reduced rust proliferation. Furthermore, transgenic poplar lines overproducing SA exhibited higher amounts of flavan-3-ols constitutively via the same transcriptional activation mechanism. These findings suggest a strong association among SA, flavan-3-ol biosynthesis, and rust resistance in poplars. Abscisic acid also promoted poplar defense against rust infection, but likely through stomatal immunity independent of flavan-3-ols. Jasmonic acid did not confer any apparent defense responses to the fungal pathogen. We conclude that SA activates flavan-3-ol biosynthesis in poplar against rust infection.
doi:10.1111/nph.15396 pmid:30168132 fatcat:2remlxm3n5gplk4x3yafg3j7pu