Abstract
While many aspects of the growth of maize are well understood, the role of cell wall feruloylation particularly during internode elongation has not been firmly established, but results so far indicate that it has significant implications for both biofuel feedstock conversion and for crop yield. The growth of the cell wall is achieved by synthesis, integration and cross-linking between wall polymers. As ferulate oxidative coupling of arabinoxylan side chains constitutes a significant type of cross-link in grass cell walls, it is expected to have a crucial role in plant growth. Making use of plants expressing an apoplast targeted Aspergillus niger FAEA under the control of either a constitutive or an inducible promoter, the role of cell wall feruloylation in maize internode expansion was investigated. Analysis of FAEA expressing plants showed that where FAEA was targeted to the apoplast under a constitutive promoter, plants varied in stature either from semi-dwarf plants with a 40–60% height reduction, to extreme dwarf mutants with over 90% reduction in plant heights compared to controls. Results indicate that disruption of cell wall feruloylation by FAEA occurs before the start of rapid internode expansion is initiated and affects the normal course of internode elongation, resulting in short internodes and dwarfed plants. In contrast, when under the inducible Lm See1 senescence promoter, FAEA activity was found to be low up to the VT stage of development but increased significantly at the VR stage as plants began to senesce, strongly suggesting that normal cell wall feruloylation is required for the process of internode expansion. In addition, with apoplast targeted expression of FAEA under control of the senescence enhanced promoter it was possible to demonstrate decreased cell wall feruloylation without affecting internode expansion or other aspects of plant development.
Highlights
The growth of plant cells can be defined as the irreversible increase in cell volume that is brought about by water uptake and controlled by the mechanical properties of the cell wall including wall-loosening followed by wall-stiffening [1]
The results show that disruption of feruloylation before internode rapid expansion is initiated by ferulic acid esterase (FAEA) expression, restrain internode expansion and results in dwarfed plants suggesting that normal cell wall feruloylation is required for the internodes to expand
The generation of maize plants which express FAEA either constitutively, or during senescence at different stages of plant development could provide a useful system to study the role of feruloylation in internode and leaf elongation and plant developmental growth
Summary
The growth of plant cells can be defined as the irreversible increase in cell volume that is brought about by water uptake and controlled by the mechanical properties of the cell wall including wall-loosening followed by wall-stiffening [1]. These processes are achieved by the cell wall regulating among other things, its polysaccharide composition and levels of crosslinking [2] which are responsible for maintaining the strength of the expanding wall to withstand the forces that induce their growth. Studies support the proposition that dimerization of ferulic acids take place within the cell wall as well as intracellularly [15,16,17]
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