Chalcone Synthase (CHS) Gene Suppression in Flax Leads to Changes in Wall Synthesis and Sensing Genes, Cell Wall Chemistry and Stem Morphology Parameters.

Magdalena Zuk,Andrzej Kotecki,Jerzy Hanuza,Dorota Richter,Lucyna Dymińska,Jan Szopa,Magdalena Działo,Jan Matuła

doi:10.3389/fpls.2016.00894

Abstract

The chalcone synthase (CHS) gene controls the first step in the flavonoid biosynthesis. In flax, CHS down-regulation resulted in tannin accumulation and reduction in lignin synthesis, but plant growth was not affected. This suggests that lignin content and thus cell wall characteristics might be modulated through CHS activity. This study investigated the possibility that CHS affects cell wall sensing as well as polymer content and arrangement. CHS-suppressed and thus lignin-reduced plants showed significant changes in expression of genes involved in both synthesis of components and cell wall sensing. This was accompanied by increased levels of cellulose and hemicellulose. CHS-reduced flax also showed significant changes in morphology and arrangement of the cell wall. The stem tissue layers were enlarged averagely twofold compared to the control, and the number of fiber cells more than doubled. The stem morphology changes were accompanied by reduction of the crystallinity index of the cell wall. CHS silencing induces a signal transduction cascade that leads to modification of plant metabolism in a wide range and thus cell wall structure.

Highlights

Plants produce more than 10 000 phenolics with diverse structures and properties (Kumar Anal et al, 2014)
Since MYB DNA binding domain transcription factor (MYB) is an important regulator of secondary wall biosynthesis in Arabidopsis (Zhong et al, 2007, 2008) and is able to bind to the promoters of lignin biosynthetic genes (Patzlaff et al, 2003; Goicoechea et al, 2005) we propose that its reduction in chalcone synthase (CHS)-suppressed flax plants might be a direct reason for lignin deficiency therein
Trans-cinnamic acid, which is the product of phenylalanine conversion catalyzed by phenylalanine/tyrosine ammonia-lyase (PAL) enzyme, is the branch point for p-coumaric acid and benzoic acid derivatives. p-Coumaric acid might be converted to coumaroyl-CoA by 4-hydroxycinnamoyl-CoA lyase (4CL) and further by cinnamate 3-hydroxylase (C3H) and hydroxycinnamoylCoA shikimate/quinate hydroxycinnamoyl transferase (HCT) to lignin or by CHS to chalcones and to proanthocyanidin and flavonoids

Summary

Introduction

Plants produce more than 10 000 phenolics with diverse structures and properties (Kumar Anal et al, 2014). The main classes of flax phenolics are: the simple phenolics, such as phenolic acids and benzoic acid derivatives; flavonoids such as vitexin; tannins such as catechin derivatives; and lignin precursors such as coniferyl aldehyde. All these compounds share the basic phenolic structure, i.e., a six-carbon phenyl ring to which a three-carbon side chain is attached in a group of phenylpropanoids (Li et al, 2010). Plant phenolics are synthesized from precursors, and the starting point is the shikimic acid pathway. The main stream is the formation of chorismic acid, which is subsequently metabolized

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