Comparative genetic analyses of WOX3 and WOX4 functions during plant development
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Comprising a deletion of a lateral compartment in maize leaves and leaf homologs, the narrow sheath (ns) phenotype is a duplicate factor trait conferred by recessive mutations at the unlinked loci ns1 and ns2. ns1 and ns2 were isolated by homology to the WUSCHEL-related homeobox gene PRESSED FLOWER (PRS/WOX3), which is required for lateral sepal development in Arabidopsis. Analyses of NS protein accumulation verified that the ns-R mutations are null alleles. ns transcripts are detected early in two lateral foci within maize meristems, and late in the margins of lateral organ primordia. Previously undiscovered leaf phenotypes in the pressed flower mutant support a model whereby the morphology of eudicot leaves and monocot grass leaves has evolved from the differential contribution of upper versus lower leaf zones. LeWOX4, an ortholog of AtWOX4, was cloned from tomato. RT-PCR and in situ hybridizations reveal that the WOX4 orthologues from both Arabidopsis and tomato are expressed in the stem cells of the vascular procambium, although these species differ in the arrangement of vascular bundles. RNAi-induced knockdown of WOX4 generated no mutant phenotype in tomato or Arabidopsis, suggesting that WOX4 may perform redundant functions in these organisms. Constitutive 35S-induced expression of WOX4 in Arabidopsis and tomato indicates that WOX4 overexpression may promote procambial activity, leaf complexity and lateral organ development. This represents the first-ever analyses of WOX4 expression and function in any plant system.