Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 107, Issue 32, Pages 14496-14501Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1009170107
Keywords
ferulate 5-hydroxylase; NAC transcription factor; pathway evolution
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Funding
- state of Oklahoma (through the Oklahoma Bioenergy Center)
- Department of Energy [DE-FG02-06ER64303]
- Department of Energy Bioenergy Research Centers, through the Office of Biological and Environmental Research in the Department of Energy Office of Science
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Lignin is a major component of plant secondary cell walls and is derived from p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) monolignols. Among higher plants, S lignin is generally considered to be restricted to angiosperms, which contain the S lignin-specific cytochrome P450-dependent monooxygenase, ferulic acid/coniferaldehyde/ coniferyl alcohol 5-hydoxylase (F5H). The transcription factor MYB58 directly regulates expression of monolignol pathway genes except for F5H. Here we show that F5H expression is directly regulated by the secondary cell wall master switch NST1/SND1, which is known to regulate expression of MYB58. Deletion of NST1 expression in Medicago truncatula leads to a loss of S lignin associated with a more than 25-fold reduction of F5H expression but only around a 2-fold reduction in expression of other lignin pathway genes. A detailed phylogenetic analysis showed that gymnosperms lack both F5H and orthologs of NST1/SND1. We propose that both F5H and NST1 appeared at a similar time after the divergence of angiosperms and gymnosperms, with F5H possibly originating as a component of a defense mechanism that was recruited to cell wall biosynthesis through the evolution of NST1-binding elements in its promoter.
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