Regulation of Compound Leaf Development

Abstract

Leaf morphology is one of the most variable, yet inheritable, traits in the plant kingdom. How plants develop a variety of forms and shapes is a major biological question. Here, we discuss some recent progress in understanding the development of compound or dissected leaves in model species, such as tomato (Solanum lycopersicum), Cardamine hirsuta and Medicago truncatula, with an emphasis on recent discoveries in legumes. We also discuss progress in gene regulations and hormonal actions in compound leaf development. These studies facilitate our understanding of the underlying regulatory mechanisms and put forward a prospective in compound leaf studies.

Keywords: Cardamine hirsuta; Medicago truncatula; compound leaf development; gene regulation; hormones; tomato.

Figure 1

Compound leaf development in inverted repeat lacking clade (IRLC) legumes. Based on the understanding of compound leaf development in Medicago truncatula and pea (Pisum sativa) belonging to the IRLC clade of legumes, a genetic model that governs compound leaf development is proposed. The class I homeodomain transcription factor KNOXI genes are expressed in the shoot apical meristem (SAM), but their expression is excluded from incipient sites of leaf primordia at the periphery of SAM and subsequent leaf primordia. Loss-of-function mutants of the FLO/LFY/UNI ortholog, SGL1, exhibit simple leaves with reduced petioles, consistent with the role of SGL1/UNI in lateral leaflet initiation and leaf proximodistal axis development. The C2H2 zinc finger transcription factor, PALM1, directly represses the expression of SGL1 to regulate its spatiotemporal expression domain. FCL1, encoding a class M KNOX protein, is required for the leaf proximodistal axis development and leaflet boundary formation. FCL1 and SGL1 act in parallel pathways, and both are required for leaf petiole development. Medicago auxin efflux PIN10 protein (MtPIN10), the Arabidopsis PIN1 ortholog, mediates auxin activity maxima that precede and are required for the initiation of leaf and leaflet primordia and leaflet serration at the distal leaflet margin. The Medicago NAM/CUC gene, MtNAM, functions in the development of lateral organ boundaries.