In this study, we identified a MYB-like gene in Medicago truncatula, AGAMOUS-LIKE FLOWER (AGLF), the null mutants of which developed homeotic transformation of stamens and carpel into petals and sepals. The relationships of AGLF with conventional ABC genes illustrated by the genetic and expression assays indicate that AGLF plays a C-function role in floral organ identity. Our work not only identifies a regulator of C-function genes, but also demonstrates the necessity of exploring the ABC models in other plant species with derived flower patterns.
Floral development is one of the model systems for investigating the mechanisms underlying organogenesis in plants. Floral organ identity is controlled by the well-known ABC model, which has been generalized to many flowering plants. Here, we report a previously uncharacterized MYB-like gene, AGAMOUS-LIKE FLOWER (AGLF), involved in flower development in the model legume Medicago truncatula. Loss-of-function of AGLFresults in flowers with stamens and carpel transformed into extra whorls of petals and sepals. Compared with the loss-of-function mutant of the class C gene AGAMOUS (MtAG) in M. truncatula, the defects in floral organ identity are similar between aglf and mtag, but the floral indeterminacy is enhanced in the aglf mutant. Knockout of AGLF in the mutants of the class A gene MtAP1 or the class B gene MtPI leads to an addition of a loss-of-C-function phenotype, reflecting a conventional relationship of AGLF with the canonical A and B genes. Furthermore, we demonstrate that AGLF activates MtAG in transcriptional levels in control of floral organ identity. These data shed light on the conserved and diverged molecular mechanisms that control flower development and morphology among plant species.
Figure 1: The aglf mutant displays an indeterminate flower phenotype. (A and B) The wild-type (WT) and aglf-1 flowers. (C) The number of sepals, petals, stamens, and carpels in WT and aglf-1. The data represent means ± SD (n = 25). (D and E) Longitudinal sections of the WT and aglf-1 flowers stained with toluidine blue. (F) A schematic illustration of floral organs in WT and aglf-1. The wild-type flower consists of four whorls of organs: sepal (green), petal (purple), stamen (orange), and carpel (blue). An aglf-1 flower consists of sepals in the first whorl, petals in the second and third whorls, and reiterations of this pattern in interior whorls. (G) SEM analysis of floral meristem in WT and aglf-1. CPab is marked in yellow, and petal primordia are marked in green. [Scale bars: (A and B) 2 mm; (D and E) 200 μm; (G) 100 µm.] A, alae; C, carpel; CP, common primordia; CPab, abaxial CP; CPad, adaxial CP; K, keel; P, petal; S, sepal; Sab, abaxial sepal; Sad, adaxial sepal; Sl, lateral sepal; ST, stamens; V, vexillum. Asterisk indicates the indeterminate primordium in aglf-1.