Abstract
Leaves in angiosperms generally have distinct adaxial(Ad)/abaxial(Ab) identity, which is required for their flattening. By contrast, many unifacial leaves, consisting of only the Ab side, show flattened morphology, implicating a unique mechanism that allows leaf flattening independent of Ad/Ab identity. Here, we report possible roles for auxin in outgrowth of unifacial leaves.
In two closely related unifacial-leafed species in Juncaceae, J. prismatocarpus with flattened leaves, and J. wallichianus with radialized leaves, the auxin-responsive gene GH3 displayed spatially different expression within leaf primordia. Treatment of J. prismatocarpus seedlings with either exogenous auxin or auxin transport inhibitors, which possibly disturb auxin distribution, eliminated flatness of leaf blades. Moreover, elimination of leaf flatness accompanied dysregulated expressions of genetic factors responsible for specifying central-marginal leaf polarity. Thus, we suggest that laminar outgrowth of unifacial leaves depends on proper distribution of auxin, which induces initial leaf flattening and subsequent differentiation of leaf polarity that may promote further marginal growth of leaves.
