plants Review The Diverse Roles of Auxin in Regulating Leaf Development Yuanyuan Xiong 1,2 and Yuling Jiao 1,2,* 1 State Key Laboratory of Plant Genomics and National Center for Plant Gene Research (Beijing), Institute of Genetics and Developmental Biology, The Innovative Academy of Seed Design, Chinese Academy of Sciences, Beijing 100101, China 2 College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China * Correspondence:
[email protected] Received: 30 June 2019; Accepted: 19 July 2019; Published: 23 July 2019 Abstract: Leaves, the primary plant organs that function in photosynthesis and respiration, have highly organized, flat structures that vary within and among species. In recent years, it has become evident that auxin plays central roles in leaf development, including leaf initiation, blade formation, and compound leaf patterning. In this review, we discuss how auxin maxima form to define leaf primordium formation. We summarize recent progress in understanding of how spatial auxin signaling promotes leaf blade formation. Finally, we discuss how spatial auxin transport and signaling regulate the patterning of compound leaves and leaf serration. Keywords: auxin; leaf blade; auxin transport; patterning; auxin signaling; compound leaf 1. Introduction Unlike animals, plants continuously produce new organs, forming leaves, flowers, and stems postembryonically. The leaf is a determinate lateral organ. Leaves bulge out at the flanks of the indeterminate shoot apical meristem (SAM), a highly organized tissue containing stem cells. A typical eudicot leaf is composed of two morphologically distinct parts: A broad, flat blade and a narrow, stem-like petiole. For most plant species, leaves are the major sites of photosynthesis.