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Plants 2013, 2(2), 317-342; doi:10.3390/plants2020317

TALE and Shape: How to Make a Leaf Different

Istituto di Biologia e Biotecnologia Agraria, UOS Roma, Consiglio Nazionale delle Ricerche, Via Salaria Km. 29,300, Monterotondo Scalo, 00015 Roma, Italy
* Author to whom correspondence should be addressed.
Received: 18 February 2013 / Revised: 10 April 2013 / Accepted: 19 April 2013 / Published: 6 May 2013
(This article belongs to the Special Issue Leaf Development)
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The Three Amino acid Loop Extension (TALE) proteins constitute an ancestral superclass of homeodomain transcription factors conserved in animals, plants and fungi. In plants they comprise two classes, KNOTTED1-LIKE homeobox (KNOX) and BEL1-like homeobox (BLH or BELL, hereafter referred to as BLH), which are involved in shoot apical meristem (SAM) function, as well as in the determination and morphological development of leaves, stems and inflorescences. Selective protein-protein interactions between KNOXs and BLHs affect heterodimer subcellular localization and target affinity. KNOXs exert their roles by maintaining a proper balance between undifferentiated and differentiated cell state through the modulation of multiple hormonal pathways. A pivotal function of KNOX in evolutionary diversification of leaf morphology has been assessed. In the SAM of both simple- and compound-leafed seed species, downregulation of most class 1 KNOX (KNOX1) genes marks the sites of leaf primordia initiation. However, KNOX1 expression is re-established during leaf primordia development of compound-leafed species to maintain transient indeterminacy and morphogenetic activity at the leaf margins. Despite the increasing knowledge available about KNOX1 protein function in plant development, a comprehensive view on their downstream effectors remains elusive. This review highlights the role of TALE proteins in leaf initiation and morphological plasticity with a focus on recent advances in the identification of downstream target genes and pathways.
Keywords: TALE; BLH; KNOX; homeobox transcription factors; target genes; leaf development; vascular development; cell fate; cell differentiation; shoot apical meristem TALE; BLH; KNOX; homeobox transcription factors; target genes; leaf development; vascular development; cell fate; cell differentiation; shoot apical meristem
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Di Giacomo, E.; Iannelli, M.A.; Frugis, G. TALE and Shape: How to Make a Leaf Different. Plants 2013, 2, 317-342.

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