Abstract
In Arabidopsis, and other plants, the RABA GTPases (orthologous to the Rab11a of mammals) have expanded in number and diversity and have been shown to belong to eight sub clades, some of which have been implicated in controlling vesicles that traffic cell wall polymers and enzymes that synthesise or modify them to the cell wall. In order to investigate this, we have investigated whether T-DNA insertion knockouts of individual RABA genes belonging to different sub clades, impact on the composition of the plant cell wall. Single gene knockouts of the RABA1, RABA2 and RABA4 sub clades primarily affected the percentage composition of pectin, cellulose and hemicellulose within the cell wall, respectively, despite having no obvious phenotype in the whole plant. We hypothesise that vesicles carrying specific types of cargoes from the Golgi to the cell surface may be regulated by particular sub types of RABA proteins, a finding that could have wider implications for how trafficking systems work and could be a useful tool in cell wall research and other fields of plant biology.
Highlights
The cell wall contains four main components, cellulose, hemicellulose, pectin and lignin with various minor contributions from proteins and inorganic compounds [1] the complexity within these constituents is magnified greatly by specific polysaccharide backbone and side chain linkages
Pectin and hemicellulose are directly transported through the trans-Golgi network (TGN) [3,5], while CESA proteins, involved in cellulose synthesis are cargoed to the plasma membrane, where cellulose synthesis occurs [6]
It has been shown that RABA2 and RABA3 proteins localise to the cell plate [20] and from this finding it was reasonable to assume that these RAB proteins were involved in cell wall deposition; their exact role was not established
Summary
The cell wall contains four main components, cellulose, hemicellulose, pectin and lignin with various minor contributions from proteins and inorganic compounds [1] the complexity within these constituents is magnified greatly by specific polysaccharide backbone and side chain linkages. De novo synthesis of the three polysaccharide components occurs in the Golgi, for pectin and hemicellulose, while cellulose synthesis occurs at the plasma membrane. In comparison with mammalian systems, Arabidopsis lacks some classes of RAB proteins, but others, most notably the RABA clade (orthologous to the Rab11a of mammals) has expanded in number, diversity and perhaps roles [8,9] and various members of the RABA clade have been implicated in trafficking to the cell wall [10]
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