Analyses of WOX4 transgenics provide further evidence for the evolution of the WOX gene family during the regulation of diverse stem cell functions.

The WOX (WUSCHEL-related homeobox) gene family of Arabidopsis comprises fifteen plant-specific transcriptional factors that play important development roles. Genetic, phylogenetic, and genomic analyses suggest that WOX genes generally act non-autonomously to organize stem-cell and initial-cell populations within plant meristems and organ anlagen. Previous cross-complementation analyses indicate that the functional diversification of distinct WOX paralogs may be explained largely by promoter evolution, although paralog-specific protein::protein interactions are also implicated. A recent report described WOX4 function during development of the procambium, which comprises the meristematic tissues of the plant vasculature. Here we show that WOX4 fails to complement PRS1/WOX3 function, when driven from the PRS1/WOX3 native promoter. These data suggest that WOX4 identifies different DNA targets and/or interacting proteins during development of the vasculature procambium than does PRS1/WOX3 during the specification of lateral organ initial cells. The identification of super-compound leaf phenotypes induced by overexpression of the SlWOX4 ortholog in tomato suggests a functional link between vascular patterning and leaf complexity.