Plant leaves show pronounced plasticity of size and form. In the classical, partially dominant mutation Lanceolate (La), the large compound leaves of tomato (Solanum lycopersicum) are converted into small simple ones. We show that LA encodes a transcription factor from the TCP family containing an miR319-binding site. Five independent La isolates are gain-of-function alleles that result from point mutations within the miR319-binding site and confer partial resistance of the La transcripts to microRNA (miRNA)-directed inhibition. The reduced sensitivity to miRNA regulation leads to elevated LA expression in very young La leaf primordia and to precocious differentiation of leaf margins. In contrast, downregulation of several LA-like genes using ectopic expression of miR319 resulted in larger leaflets and continuous growth of leaf margins. Our results imply that regulation of LA by miR319 defines a flexible window of morphogenetic competence along the developing leaf margin that is required for leaf elaboration.

not deal with the reasonableness of the charges made in terms of the amount charged (which is left to other authorities) but rather with the medical necessity of the services. PSROs, thus conceived, would be a governmentsponsored body, designed to scrutinize hospitals-and through them, doctors-in a kind of independent medical audit.To avoid dealing with several millions of patients the PSRO setup calls for high reliance on "good conduct" and on computers. Providers who have demonstrated that they treat patients within defined "norms" will be exempted from the need for prior approval. The internal review committees of these providers will then themselves act as certifying agents. But even the services of these approved facilities will continue to be monitored by computers. The weight of the forms to be filled out alone may serve to Continued on p. 507