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 plantspecific transcriptional factors that play important development roles. Genetic, phylogenetic and genomic analyses suggest that WOX genes generally act nonautonomously 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.