Leaf Development in Medicago truncatula

Abstract

Forage yield is largely dependent on leaf development, during which the number of leaves, leaflets, leaf size, and shape are determined. In this mini-review, we briefly summarize recent studies of leaf development in Medicago truncatula, a model plant for legumes, with a focus on factors that could affect biomass of leaves. These include: floral development and related genes, lateral organ boundary genes, auxin biosynthesis, transportation and signaling genes, and WOX related genes.

Keywords: Medicago; leaf development; leaf shape; leaf size; leaflet number; morphogenesis.

Figure 1

(a) Gene networks controlling compound leaf development of Medicago truncatula at the initiation stage. KNOX I genes are expressed in SAM and down regulated in leaf primordia. PHAN and SGL1 are expressed at both SAM and early-stage leaf primordia during development. HDL is expressed in the organization center of the SAM. SLM1 and SGL1 are expressed at early-stage leaf primordia. FCL1, LLS1, and CUC genes are expressed at the boundary between SAM and leaf primordia. (b) Gene networks controlling the compound leaf development of Medicago truncatula at the morphogenesis stage. PALM1 is expressed at lateral leaflet primordia and PINNA1 is expressed at the distal region of terminal leaflet primordia. SGL1 is restricted to the basal region of the terminal leaflet primordia by PALM1 and PINNA1. LLS1 and CUC are expressed at the boundary between terminal leaflet primordia and lateral leaflet primordia. HDL is expressed at the axis between the terminal leaflet primordia and lateral leaflet primordia to suppress extra leaflet primordia outgrowth. REV is expressed at the adaxial portion of leaf primordia to regulate auxin-related genes. AGO7 and PHAN repress ARF3, which represses PALM1 during leaf morphogenesis. STF is expressed at the boundary between the adaxial–abaxial domain to restrict the expression of AS2 and WOX9. (c) Genes control lamina size and shape at the differentiation stage. HDL promotes margin serration and lamina length/width ratio, while MIO1 promote cell proliferation to promote lamina size. TL: terminal leaflet. LL: lateral leaflets. ST: stipules. Ab: Abaxial. Ad: Adaxial.