NaAGP4 is an arabinogalactan protein whose expression is suppressed by wounding and fungal infection inNicotiana alata

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Abstract
Arabinogalactan proteins (AGPs) are proteoglycans secreted by plant cells that have been implicated in plant growth and development. Most AGPs cloned to date possess highly labile glycosylphosphatidylinositol (GPI) lipid anchors. These anchors transiently attach AGPs to the plasma membrane before they are released into the cell wall following GPI anchor hydrolysis. We have isolated and partially sequenced the protein core of an AGP purified from styles ofNicotiana alata. The protein sequence data were utilised to clone the AGP's gene,NaAGP4. This AGP shares about 78% sequence identity with the tomato AGP LeAGP-1. RNA gel blot analyses of different plant organs indicate thatNaAGP4 is expressed in the same tissues and at similar levels asLeAGP-1. Furthermore,NaAGP4 likeLeAGP-1 is rapidly suppressed by tissue wounding and by pathogen infection. We believe NaAGP4 and LeAGP-1 are the first described examples of orthologous AGPs from different plant species. In contrast, another AGP fromN. alata, NaAGP1, is comparatively unaffected by wounding and pathogen infection, although this AGP is expressed in similar tissues and at similar levels as NaAGP4.