Genetic Interactions That Regulate Inflorescence Development in Arabidopsis

Abstract

In Arabidopsis, floral meristems arise in continuous succession directly on the flanks of the inflorescence meristem. Thus, the pathways that regulate inflorescence and floral meristem identity must operate both simultaneously and in close spatial proximity. The TERMINAL FLOWER 1 (TFL1) gene of Arabidopsis is required for normal inflorescence meristem function, and the LEAFY (LFY), APETALA 1 (AP1), and APETALA 2 (AP2) genes are required for normal floral meristem function. We present evidence that inflorescence meristem identity is promoted by TFL1 and that floral meristem identity is promoted by parallel developmental pathways, one defined by LFY and the other defined by AP1/AP2. Our analysis suggests that the acquisition of meristem identity during inflorescence development is mediated by antagonistic interactions between TFL1 and LFY and between TFL1 and AP1/AP2. Based on this study, we propose a simple model for the genetic regulation of inflorescence development in Arabidopsis. This model is discussed in relation to the proposed interactions between the inflorescence and the floral meristem identity genes and in regard to other genes that are likely to be part of the genetic hierarchy regulating the establishment and maintenance of inflorescence and floral meristems.

Photo and hormonal control of meristem identity in the Arabidopsis flower mutants apetala2 and apetala1.

“…These ectopic secondary or axillary flowers may in turn produce tertiary axillary flowers. By contrast, apl-7 ap2-7 double mutants produce flowers that are more indeterminate and inflorescence-like than either single mutant alone (Irish and Sussex, 1990;Bowman et al, 1993;Schultz and Haughn, 1993;Shannon and Meeks-Wagner, 1993). …”

“…In addition to its functions in the control of floral organ identity, AP2 has also been shown to control the establishment of flower meristem identity, in part through its interaction with the floral meristem identity gene AP7 (Irish and Sussex, 1990;Bowman et al, 1993;Shannon and Meeks-Wagner, 1993). Strong apl mutants produce highly branched, inflorescence-like flowers that are characterized by the lack of petals, by the replacement of sepals with bractlike leaves, and by the production of ectopic secondary flowers in the axils of the first-whorl leaves (Irish and Sussex, 1990;Bowman et al, 1993;Schultz and Haughn, 1993).…”

Repression of AGAMOUS-LIKE 24 is a crucial step in promoting flower development

“…Floral meristem identity genes LEAFY (LFY) and APETALA1 (AP1) promote establishment and maintenance of floral identity in newly formed floral primordia [1][2][3][4][5][6][7][8][9] . Without their activity, the floral primordia develop with inflorescence characteristics.…”

“…6,7,9). Previous studies have shown that TFL1 acts predominantly to oppose establishment of floral meristem identity but does not antagonize the maintenance of floral meristems 6,7,[10][11][12] . The simple establishment of floral meristem identity is insufficient to guarantee floral identity, as indicated by the observation that a floral meristem can revert to a flower-generating inflorescence meristem, a phenomenon called floral reversion 5,[13][14][15] .…”

A common mechanism controls the life cycle and architecture of plants

“…It has been suggested that floral meristem identity genes such as LFY and AP1 act as mutual antagonists with TFL1, to ensure that floral meristems pursue a separate determinate growth pattern from the indeterminate inflorescence meristem which produced them (Shannon and Meeks-Wagner, 1993;Schultz and Haughn, 1993). This stand-point is supported by the complementary phenotypes of the tfl1 mutant (where flowers replace inflorescences) when compared to those of lfy and ap1 mutants (where inflorescences replace flowers).…”