Abstract
Lignin, a major component of the secondary cell wall, is important for plant growth and development. Moreover, lignin plays a pivotal role in plant innate immunity. Lignin is readily deposited upon pathogen infection and functions as a physical barrier that limits the spread of pathogens. In this study, we show that an Arabidopsis MYB transcription factor MYB15 is required for the activation of lignin biosynthesis genes such as PAL, C4H, 4CL, HCT, C3′H, COMT, and CAD, and consequently lignin formation during effector-triggered immune responses. Upon challenge with the avirulent bacterial pathogen Pst DC3000 (AvrRpm1), lignin deposition and disease resistance were reduced in myb15 mutant plants. Furthermore, whereas invading pathogens, together with hypersensitive cell death, were restricted to the infection site in wild-type leaves, they spread beyond the infected area in myb15 mutants. The exogenous supply of the lignin monomer coniferyl alcohol restored lignin production and rescued immune defects in myb15 plants. These results demonstrate that regulation at the transcriptional level is key to pathogen-induced lignification and that MYB15 plays a central role in this process.
Highlights
Lignin is an organic polymer that serves as a major structural molecule of the secondary cell wall in plant vascular systems (Vanholme et al, 2010)
MYB15 is Required for the Expression of Lignin Biosynthesis Genes in effector-triggered immunity (ETI)
We showed that intense lignin deposition is induced at the infection site of leaves challenged with avirulent bacterial pathogens (Lee et al, 2019)
Summary
Lignin is an organic polymer that serves as a major structural molecule of the secondary cell wall in plant vascular systems (Vanholme et al, 2010). Lignin composition and content vary among different species, tissues, and cells, influencing plant physiology and development (Wang et al, 2013). Given its importance in plant development and biotechnological applications, lignin metabolism has been extensively studied in model plants, woody trees, and grass biomass crops (Vanholme et al, 2010; Wang et al, 2013; Liu et al, 2018; Umezawa, 2018). Lignin polymers are composed primarily of monolignols, coniferyl, sinapyl, and p-coumaryl alcohols, which are oxidatively cross-linked to generate guaiacyl (G), syringyl (S), and p-hydroxyphenyl (H) units, respectively (Boerjan et al, 2003). Whereas p-coumaryl alcohol is synthesized by a subset of enzymes, phenylalanine ammonia lyase
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