LEAFY and APETALA1 down-regulate ZINC FINGER PROTEIN 1 and 8 to release their repression on class B and C floral homeotic genes.

Abstract

Organ initiation from the shoot apical meristem first gives rise to leaves during vegetative development and then flowers during reproductive development. <i>LEAFY</i> (<i>LFY</i>) is activated after floral induction and together with other factors promotes the floral program. LFY functions redundantly with APETALA1 (AP1) to activate the class B genes <i>APETALA3</i> (<i>AP3</i>) and <i>PISTILLATA</i> (<i>PI</i>), the class C gene <i>AGAMOUS</i> (<i>AG</i>), and the class E gene <i>SEPALLATA3</i>, which leads to the specification of stamens and carpels, the reproductive organs of flowers. Molecular and genetic networks that control the activation of <i>AP3,</i> <i>PI,</i> and <i>AG</i> in flowers have been well studied; however, much less is known about how these genes are repressed in leaves and how their repression is lifted in flowers. Here, we showed that two genes encoding <i>Arabidopsis</i> C2H2 ZINC FINGER PROTEIN (ZFP) transcription factors, ZP1 and ZFP8, act redundantly to directly repress <i>AP3,</i> <i>PI,</i> and <i>AG</i> in leaves. After <i>LFY</i> and <i>AP1</i> are activated in floral meristems, they down-regulate <i>ZP1</i> and <i>ZFP8</i> directly to lift the repression on <i>AP3,</i> <i>PI,</i> and <i>AG</i>. Our results reveal a mechanism for how floral homeotic genes are repressed and derepressed before and after floral induction.