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.
Bibliographical noteFunding Information:
We wish to thank E. Lifschitz5 (Technion), the C.M. Rick Tomato Genetics Resource Center and Clemson University Genomics Institute for materials, Navot Ori for unearthing la-6, and R. Fluhr, E. Hornstein, Z. Lippman, D. Weigel, S. Hake, J. Bowman and members of our laboratories for discussions and criticism. The work was supported by grants from the US-Israel Binational Agricultural Research and Development Fund, the European Union (MechPlant project) and the Israel Science Foundation (ISF) to N.O.; from ISF, MINERVA, The US-Israel Binational Science Foundation and Lubin Center for Plant Biotechnology to Y.E.; from the German-Israeli Foundation for Scentific Research and Development to Y.E. and N.O.; and from the German-Israeli Project Cooperation to Y.E. and D.Z.