Robust control of floral meristem determinacy by position-specific multifunctions of KNUCKLES.

Abstract

Floral organs are properly developed on the basis of timed floral meristem (FM) termination in <i>Arabidopsis</i> In this process, two known regulatory pathways are involved. The <i>WUSCHEL</i> (<i>WUS</i>)-<i>CLAVATA3</i> (<i>CLV3</i>) feedback loop is vital for the spatial establishment and maintenance of the FM, while <i>AGAMOUS</i> (<i>AG</i>)-<i>WUS</i> transcriptional cascades temporally repress FM. At stage 6 of flower development, a C2H2-type zinc finger repressor that is a target of AG, KNUCKLES (KNU), directly represses the stem cell identity gene <i>WUS</i> in the organizing center for FM termination. However, how the robust FM activity is fully quenched within a limited time frame to secure carpel development is not fully understood. Here, we demonstrate that KNU directly binds to the <i>CLV1</i> locus and the cis-regulatory element on <i>CLV3</i> promoter and represses their expression during FM determinacy control. Furthermore, KNU physically interacts with WUS, and this interaction inhibits <i>WUS</i> from sustaining <i>CLV3</i> in the central zone. The KNU-WUS interaction also interrupts the formation of WUS homodimers and WUS-HAIRYMERISTEM 1 heterodimers, both of which are required for FM maintenance. Overall, our findings describe a regulatory framework in which KNU plays a position-specific multifunctional role for the tightly controlled FM determinacy.